DE10114972B4 - Device for cleaning the exhaust gas of an internal combustion engine - Google Patents

Abstract

Device for cleaning the exhaust gas of an internal combustion engine, comprising a particle filter arranged in the exhaust system, on which the retained particles are oxidized, and a bypass line through which the exhaust gas can bypass the particle filter, the particle filter oxidizing a certain amount of particles depending on the temperature of the particle filter and if an amount of injected fuel is less than a predetermined amount, causing a portion of the exhaust gas to take the detour through the bypass line, the amount of bypassed exhaust gas being determined based on the amount of injected fuel.

Description

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to a device for cleaning the exhaust gas of an internal combustion engine.

2. Description of the Related Art

The exhaust gas of an internal combustion engine, and in particular a diesel engine, contains particulate matter comprising carbon as a main component. Particulates are harmful materials and therefore it has been proposed to provide a particulate filter in the exhaust system to retain the particles before they escape into the atmosphere. In such a particulate filter, the retained particles must be burned and eliminated to prevent an increase in the resistance to the exhaust due to clogged mesh.

With such regeneration of the particulate filter, if the temperature of the particulate rises above about 600 ° C, it ignites and burns. However, the temperature of the exhaust gas of a diesel engine is usually much lower than 600 ° C, and therefore a heater is needed to heat the particulate filter itself.

Examined Japanese Patent Publication JP 7-106 290 B4 discloses that when a platinum group metal and an alkaline earth metal oxide rest on the filter, the particles burn on the filter and are successively removed at about 400 ° C. 400 ° C is a common temperature for the exhaust gas of a diesel engine.

However, when the above-mentioned filter is used, the temperature of the exhaust gas is not always about 400 ° C. In addition, a large amount of particulates may be ejected from the engine. Thus, particles that can not be burned each time can be deposited on the filter.

When a certain amount of particulate settles on the filter, the ability to burn and remove particulates from the filter decreases so much that the filter can not regenerate itself. Therefore, if only such a filter is placed in the exhaust system, clogging of the filter meshes may occur relatively quickly.

DE 38 16 233 C1 discloses a soot particle filter disposed in the exhaust pipe system of an internal combustion engine. In addition, a bypass line for the exhaust gas is provided, in which the exhaust gases can bypass the soot particle filter. Depending on whether the motor speed or the motor temperature exceeds or falls below specified limits, the bypass line is either completely opened or closed, ie the complete exhaust gas flow is conducted through either the soot particle filter or the bypass line.

US 58 39 274 A discloses an exhaust gas catalyst control system with a catalytic converter. The catalytic converter converts hydrocarbon and carbon monoxide. Oxygen is needed for the conversion and the exhaust methane concentration is determined.

SUMMARY OF THE INVENTION

Therefore, it is an object of this invention to provide an apparatus for purifying the exhaust gas of an internal combustion engine which can prevent clogging of the meshes of the particulate filter by particles retained thereon.

The invention relates to a device for cleaning the exhaust gas of an internal combustion engine according to any one of claims 1, 4, 5 and 8.

Preferred embodiments thereof are the subject matter of claims 2, 3, 6, 7, 9 and 10.

According to this invention, there is provided a first apparatus for purifying the exhaust gas of an internal combustion engine, comprising an exhaust gas particulate filter on which the retained particulates are oxidized and a bypass conduit through which the exhaust gas can bypass the particulate filter, the particulate filter depending on the temperature of the particulate filter can oxidize and eliminate a certain amount of particulates, and, when an amount of injected fuel is less than a predetermined amount, a part of the exhaust gas is caused to bypass the bypass line, the amount of the recirculated exhaust gas being based on the Amount of injected fuel is determined.

According to this invention, there is provided a second apparatus for purifying the exhaust gas of an internal combustion engine comprising an exhaust gas particulate filter on which the retained particulates are oxidized and a bypass conduit through which the exhaust gas can bypass the particulate filter, the particulate filter being a release agent for active oxygen, active oxygen released from the active oxygen release agent carries the retained particles on the particulate filter oxidized, the active oxygen release agent NO _x to combine the NO _x with oxygen when there is an excess of oxygen in the environment, and release combined NO _x / oxygen, thereby degrading to NO _x and active oxygen as the ambient oxygen concentration decreases, the particulate filter becomes dependent on the temperature of the particulate filter can oxidize and eliminate a certain amount of particulates, and, if the amount of injected fuel is less than a predetermined amount, causing a portion of the exhaust gas to bypass the bypass, the amount of bypassed exhaust gas being based on the amount of fuel injected is determined.

According to this invention, there is provided a third apparatus for purifying the exhaust gases of an internal combustion engine, comprising an exhaust gas particulate filter on which the retained particulates are oxidized and a bypass conduit through which the exhaust gas can bypass the particulate filter, the particulate filter depending on the temperature of the particulate filter can oxidize and eliminate a certain amount of particulates, and, when a temperature of the exhaust gas is lower than a predetermined temperature, a part of the exhaust gas is caused to bypass the bypass, the amount of the recirculated exhaust gas being based on the Temperature of the exhaust gas is determined.

According to this invention, there is provided a fourth apparatus for purifying the exhaust gas of an internal combustion engine comprising an exhaust gas particulate filter on which the retained particulates are oxidized and a bypass conduit through which the exhaust gas can bypass the particulate filter, the particulate filter being a release agent containing active oxygen, the retained particles oxidized by Feisetzungsmittel of active oxygen released active oxygen on the particulate filter, holding the release agent for the active oxygen NO _x to combine the NO _x with oxygen when an excess of oxygen in the area is available, and releases the combined NO _x / oxygen to degrade it to NO _x and active oxygen as the concentration of oxygen in the environment decreases, the particulate filter can oxidize and eliminate a certain amount of particulates depending on the temperature of the particulate filter, and, when an exhaust gas temperature is lower than a predetermined temperature, a part of the exhaust gas is made to take the detour through the bypass line, wherein the amount of the recirculated exhaust gas is determined based on the temperature of the exhaust gas.

The invention will be better understood from the description of the preferred embodiments of the invention given below together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings mean:

1 is a schematic vertical sectional view of a four-stroke diesel engine with an apparatus for purifying the exhaust gas according to the invention;

2 is an enlarged vertical sectional view of the combustion chamber of 1 ;

3 is a bottom view of the cylinder head of 1 ;

4 is an enlarged vertical sectional view of the combustion chamber of 1 ;

5 is a view showing the relationship between the degree of increase of the intake valve and the exhaust valve and the fuel injection;

6 Fig. 13 is a view showing the amount of generated smoke, NO _x, and the like;

7 (A) and 7 (B) are views showing combustion pressure;

8th is a view showing the fuel molecules;

9 Fig. 13 is a view showing the relationship between the amount of NO _x generated and the EGR rate;

10 FIG. 14 is a view showing the relationship between the amount of injected fuel and the amount of mixed gas; FIG.

11 Fig. 12 is a view showing the first operating area (I) and the second operating area (II);

12 is a view showing the output of the air-fuel ratio sensor.

13 Fig. 12 is a view showing the opening degree of the throttle valve and the like;

14 is a view showing the air / fuel ratio in the first operating range (I);

15 (A) is a view showing the target opening degree of the throttle valve.

15 (B) Fig. 13 is a view showing the target opening degree of the EGR control valve;

16 is a view showing the air / fuel ratio in the second operating range (II);

17 (A) Fig. 13 is a view showing the target opening degree of the throttle valve;

17 (B) Fig. 13 is a view showing the target opening degree of the EGR control valve;

18 FIG. 10 is a plan view showing the switching section and the particulate filter in the exhaust system in close proximity according to an embodiment; FIG.

19 is a side view of 18 ;

20 is a view showing the other shut-off position of the valve housing in the switching section, which differs from the in 18 different;

21 Fig. 13 is a view showing the center position of the valve housing in the switching section;

22 (A) Fig. 10 is a front view showing the structure of the particulate filter;

22 (B) Fig. 16 is a side sectional view showing the structure of the particulate filter.

23 (A) and 23 (B) are views that explain the oxidizing effect of the particles;

24 Fig. 12 is a view showing the relationship between the amount of particles that can be oxidized and removed and the temperature of the particulate filter;

25 (A) . 25 (B) and 25 (C) are views that explain the process of settling particles;

26 Fig. 10 is a first flowchart for preventing the particulate from settling on the particulate filter;

27 Fig. 12 is a second flow chart for preventing the particles from settling on the particulate filter;

28 (A) and 28 (B) are enlarged sectional views of the partition wall of the particulate filter;

29 Fig. 10 is a plan view showing the switching section and the particulate filter in the exhaust system close up according to another embodiment;

30 FIG. 11 is a plan view showing the switching section and the particulate filter in the exhaust system in close proximity according to another embodiment. FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENT

1 Fig. 12 is a schematic vertical sectional view of a four-stroke diesel engine having an apparatus for purifying the exhaust gas according to this invention. 2 is an enlarged vertical sectional view of a combustion chamber of the diesel engine of 1 , 3 is a bottom view of a cylinder head of the diesel engine of 1 , 1 - 3 : The reference number 1 denotes a motor housing, the reference numeral 2 denotes a cylinder block, the reference numeral 3 denotes a cylinder head, the reference numeral 4 denotes a piston, the reference numeral 5a denotes a cavity located on the upper surface of the piston 4 is formed, the reference number 5 denotes a combustion chamber in the cavity 5a is formed, the reference number 6 denotes an electrically controlled fuel injector, the reference numeral 7 denotes a pair of intake valves, the reference numeral 8th denotes a suction port and the reference numeral 9 denotes a pair of exhaust valves, and the reference numeral 10 denotes an exhaust port. The intake opening 8th is via a corresponding intake pipe 11 with a surge tank 12 connected. The expansion tank 12 is via a suction channel 13 with an air filter 14 connected. A throttle valve 16 that by an electric motor 15 is driven, is in the intake 13 arranged. On the other side is the exhaust port 10 with an exhaust manifold 17 connected.

As in 1 shown is a sensor 21 for the air / fuel ratio in the exhaust manifold 17 arranged. The exhaust manifold 17 and the expansion tank 12 are via an EGR line 22 connected with each other. An electronically controlled EGR control valve 23 is in the EGR leadership 22 arranged. An EGR cooler 24 is about the EGR line 22 arranged to control the EGR gas passing through the EGR line 22 flows, to cool. In the embodiment of 1 the engine cooling water gets into the EGR cooler 24 and therefore the EGR gas is cooled with the engine cooling water.

On the other side is every fuel injector 6 connected to the fuel tank, that is, via a fuel supply pipe 25 with a common pressure line (Common Rail) 26 , Fuel becomes the common rail 26 from an electronically controlled variable fuel discharge pump 27 fed. Fuel that has been supplied to the common rail becomes the fuel injector 6 over the fuel supply pipe 25 fed. A fuel pressure sensor 28 for determining the fuel pressure in the common rail 26 is at the common rail 26 attached. The discharge amount of the fuel pump becomes due to an output signal of the fuel pressure sensor 28 controlled so that from the fuel pressure in the common rail 26 the target fuel pressure is.

The reference number 30 denotes an electronic control unit. It consists of a digital computer and is equipped with a ROM (Read Only Memory) 32 , a RAM (Random Access Memory) 33 , a CPU (microprocessor) 34 , an entrance port 35 and an exit port 36 equipped with each other through a bidirectional bus 31 are connected. The output signals of the air / fuel sensor 32 and the fuel pressure sensor 28 be in the input port 35 each via an A / D converter 37 entered. An engine load sensor 41 is with the gas pedal 40 connected, which produces an output voltage proportional to the degree of reduction (L) of the accelerator pedal 40 is. The output signal of the engine load sensor 41 is also via the A / D converter 37 in the entrance port 35 entered. In addition, the output of a crank angle sensor 42 which generates an output pulse each time the crankshaft rotates, for example, by 30 degrees, into the input port 35 entered. The fuel injector 6 , the electric motor 15 , the EGR control valve 23 and the fuel pump 27 are each via a control circuit 38 with the output port 36 connected to be driven due to the input signals.

As in the 2 and 3 shown includes the fuel injector 6 in the embodiment of this invention, a nozzle with six nozzle openings. Fuel spatters (F) are sprayed from the nozzle openings in a slight downward direction at equal angular intervals against a horizontal plane. As in 3 2, two fuel spatters (F) of the six fuel spatters (F) are shown along the lower surface of each exhaust valve 9 atomized. The 2 and 3 show the case where fuel is injected at the end of the compression stroke. In this case, the fuel spatters (F) reach the edge of the inner surface of the cavity 5 and are then inflamed and burned.

4 shows the case where additional fuel from the fuel injector 6 is injected when the lifting degree of the exhaust valves has reached the maximum of the exhaust stroke. This means, 5 FIG. 12 shows the case where the main fuel injection (Qm) is performed near the upper compression dead center and then the additional fuel injection (Qa) is performed in the middle stage of the exhaust stroke. In this case, the fuel spatters (F) that move toward the exhaust valves become between the umbrella-like back surface of the exhaust valve 9 and the exhaust port 10 directed. In other words, two nozzle openings of the six nozzle openings of the fuel injector 6 are shaped so that the fuel spatters (F) when the exhaust valves 9 are opened and the additional fuel injection (Qa) is performed, between the back surface of the exhaust valve 9 and the exhaust port 10 be steered. In the embodiment of 4 meet these fuel splashes (F) on the back surface of the exhaust valve 9 on and off the back surface of the exhaust valve 9 thrown back and become so in the exhaust port 10 directed.

Usually, the additional fuel injection (Qa) is not performed and only the main fuel injection (Qm) is performed. 6 FIG. 14 shows an example of an experiment that shows the change of the output torque and the ejected amount of smoke, HC, CO and NO _x at the time when the air-fuel ratio A / F (abscissa in FIG 6 ) by changing the opening degree of the throttle valve 16 is changed and shows the EGR rate at the time of low engine load operation. How out 6 In this experiment, the lower the air-fuel ratio A / F becomes, the higher the EGR rate becomes. When the air / fuel ratio is below the stoichiometric air / fuel ratio (almost equal to 14.6), the EGR rate rises above 65 percent.

When the EGR rate is increased to decrease the air / fuel ratio A / F as in 6 As the EGR rate approaches 40 percent and the A / F air / fuel ratio approaches approximately 30, the amount of smoke produced begins to increase. Then, as the EGR rate is further increased and the air / fuel ratio A / F is decreased, the amount of smoke produced sharply increases and reaches its peak. Then, as the EGR rate is further increased and the air-fuel ratio A / F is decreased, the amount of generated smoke sharply decreases. When the EGR rate reaches over 65 percent and the A / F air-fuel ratio approaches 15.0, the amount of smoke produced is virtually zero. This means that almost no soot is produced. At this time, the output torque of the engine drops slightly and the amount of NOx produced becomes significantly lower. On the other hand, at this time, the amounts of generated HC and CO begin to increase.

7 (A) shows the changes in the combustion pressure in the combustion chamber 5 when the crowd of the generated smoke is the largest in the vicinity of an air-fuel ratio A / F of 21. 7 (B) shows the changes in the combustion pressure in the combustion chamber 5 when the amount of generated smoke near an air-fuel ratio A / F of 18 is practically zero. As from the comparison of 7 (A) and 7 (B) becomes clear, the combustion pressure is in 7 (B) shown case in which the amount of smoke produced is practically zero, lower than in 7 (A) shown case in which the amount of smoke produced is large.

The following can be deduced from the results of the 6 and 7 conclude the experiment shown. Namely, first, when the air / fuel ratio A / F is lower than 15.0 and the amount of generated smoke is practically zero, the amount of NO _x generated considerably decreases, as in FIG 6 shown. The fact that the amount of NO _{x produced} decreases means that the combustion temperature in the combustion chamber 5 drops. Therefore, it can be said that when almost no soot is generated, the combustion temperature in the combustion chamber 5 sinks. The same thing can happen 7 be inferred. That is, at the stage that is in 7 (B) is shown in which almost no soot is generated, the combustion pressure becomes lower, therefore, the combustion temperature in the combustion chamber becomes 5 lower at this time.

Secondly, when the amount of smoke produced, that is the amount of soot produced, becomes practically zero, as in 6 As shown, the amount of HC and CO discharged increases. That is, the hydrocarbons are expelled without becoming soot. That is, the straight-chain hydrocarbons and the aromatic hydrocarbons contained in the fuel and in 8th are decomposed when their temperature is raised in the state of oxygen deficiency, resulting in the formation of a carbon black precursor. Then, soot is produced, which is composed mainly of the solid masses of carbon atoms. In this case, the actual process of making soot is complicated. How the soot precursor is formed is not clear, but anyway, the hydrocarbons that are in 8th are turned into carbon black by the soot precursor. As explained above, therefore, when the amount of soot produced becomes practically zero, the amount of HC and CO discharged increases as in FIG 6 but the HC at this time is a soot precursor or is in a hydrocarbon state before this.

In summary, these considerations are based on the experiments presented in 6 and 7 are shown: when the combustion temperature in the combustion chamber 5 is low, the amount of soot produced becomes practically zero. At this time, a soot precursor or a hydrocarbon state ahead of it becomes out of the combustion chamber 5 emitted. More detailed experiments and studies were carried out. As a result, it was recognized that when the temperature of the fuel and the gas around the fuel in the combustion chamber 5 is below a certain temperature, the process of soot formation stops halfway, that is, no soot is generated at all, and that when the temperature of the fuel and the gas around the fuel in the combustion chamber 5 rises above the certain temperature, soot is generated.

The temperature of the fuel and the gas around the fuel at the time of stopping the growth process of hydrocarbons at the stage of the soot precursor, that is, the above certain temperature, changes depending on various factors such as the fuel type, the air / fuel ratio and the compression ratio therefore they can not predict exactly, but this certain temperature is closely related to the amount of nO _x produced together. Therefore, this particular temperature can be determined to some extent from the amount of NO _x produced. That is, the larger the EGR rate, the lower the temperature of the fuel and the gas surrounding it at the time of combustion and the lower the amount of NO _x generated. At the time when the amount of generated NO _x becomes about 10 ppm or less, almost no soot is generated. Therefore, the above certain temperature substantially corresponds to the temperature at the time when the amount of generated NO _x becomes about 10 ppm or less.

Once soot has been produced, it is impossible to purify it by aftertreatment with a catalyst having an oxidation function. In contrast, a carbon black precursor or a hydrocarbon state thereof may be easily purified by a post-treatment by means of a catalyst having an oxidation function. Therefore, it is extremely effective for purifying exhaust gas that the hydrocarbons from the combustion chamber 5 in the form of a soot precursor or a state before that with the reduction in the amount of NO _x generated.

In order to stop the growth of the hydrocarbons in the stage before the soot production, it is now necessary to control the temperature of the fuel and the surrounding gas at the time of combustion in the combustion chamber 5 to lower to a temperature below the temperature at which soot is generated. In this case, it has been found that the heat-absorbing effect of the gas surrounding the fuel at the time of combustion of the fuel has an extremely great effect in lowering the temperature of the fuel and the gas surrounding it.

That is, when only air surrounds the fuel, the vaporized fuel immediately reacts with the oxygen in the air and burns. In this case, the temperature of the air at some distance from the fuel does not rise so much. Only the temperature around the fuel becomes extremely high locally. That is, at this time, the air at some distance from the fuel scarcely absorbs the heat of combustion of the fuel. In this case, as the combustion temperature locally becomes extremely high, the unburned hydrocarbons which absorb the heat of combustion generate soot.

On the other hand, when fuel is in a mixed gas of a large amount of inert gas and a small amount of air, the situation is somewhat different. In this case, the vaporized fuel disperses into the environment and reacts with the oxygen mixed with the inert gas and burns. In this case, the heat of combustion is absorbed by the surrounding inert gas, so that the combustion temperature does not increase so much. That is, the combustion temperature can be kept low. That is, the presence of inert gas plays an important role in lowering the combustion temperature. It is possible to keep the combustion temperature low by the heat absorbing effect of the inert gas.

In this case, in order to lower the temperature of the fuel and the gas surrounding it to a temperature below the temperature at which soot is generated, a sufficiently large amount of inert gas is necessary to absorb a sufficient amount of heat to the temperature to lower. Therefore, as the amount of fuel increases, the amount of inert gas required also increases. Note that the larger the specific heat of the inert gas in this case, the stronger the heat-absorbing effect becomes. Therefore, a gas having a high specific heat is preferable as an inert gas. In this connection, since CO ₂ and EGR gas have a relatively high specific heat, it is preferable to use EGR gas as an inert gas.

9 Fig. 12 shows the relationship between the EGR rate and the smoke when EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, the curve (A) in 9 shows the case that the EGR gas is strongly cooled and the temperature of the EGR gas is kept at about 90 ° C, the curve (B) shows the case that the EGR gas is cooled by a compact refrigerator, and the Curve (C) shows the case that the EGR gas is not forcibly cooled.

When the EGR gas is strongly cooled, as from curve (A) in 9 As shown, the amount of soot produced reaches its peak when the EGR rate is slightly below 50 percent. In this case, when the EGR rate is increased above 65 percent or above, almost no soot is produced.

On the other hand, when the EGR gas is cooled slightly, as from curve (B) in FIG 9 As shown, the amount of soot produced reaches its peak when the EGR rate is slightly above 50 percent. In this case, if the EGR rate is increased above 65 percent, almost no soot is produced.

In addition, if the EGR gas is not forcibly cooled as shown by the curve (C) in FIG 9 As shown, the amount of soot produced reaches its peak near an EGR rate of 55 percent. In this case, when the EGR rate is increased above 70 percent, almost no soot is produced.

Note that 9 the amount of smoke produced when the engine load is relatively high. As the engine load becomes smaller, the EGR rate at which the amount of soot produced reaches its peak falls a little, and the lower limit of the EGR rate at which almost no soot is generated also falls off a little. In this way, the lower limit of the EGR rate at which almost no soot is generated changes in accordance with the degree of cooling of the EGR gas or the engine load.

10 FIG. 12 shows the amount of mixed gas of EGR gas and air, the proportion of air in the mixed gas, and the proportion of EGR gas in the mixed gas necessary to raise a temperature from the temperature of the fuel and the gas surrounding it at the time of combustion lower than the temperature at which soot is generated in the case of using EGR gas as the inert gas. Note that in 10 the ordinate the total amount of the into the combustion chamber 5 recorded intake gas shows. The broken line (Y) shows the total amount of intake gas entering the combustion chamber 5 can be recorded if no overload is made. In addition, the abscissa shows the required load. (Z1) shows the operating range with low engine load.

10 : The proportion of air, that is, the amount of air in the mixed gas, shows the amount of air needed to cause the injected fuel to burn completely. That is, in the 10 As shown, the ratio of the amount of air and the amount of injected fuel becomes the stoichiometric air-fuel ratio. On the other hand, in 10 the proportion of EGR gas, that is, the amount of EGR gas in the mixed gas, the minimum amount of EGR gas required to make the temperature of the fuel and the surrounding gas at a temperature lower than the temperature at which soot is generated when the injected fuel has been completely burned. This amount of EGR gas, expressed as EGR rate, is equal to or greater than 55 percent; in the embodiment shown in FIG. 1, it is equal to or greater than 70 percent. That is, when the total amount of intake gas entering the combustion chamber 5 is taken to the solid line (X) in 10 is made and the ratio between the amount of air and the amount of EGR gas in the total amount of the intake gas (X) to in 10 is made, the temperature of the fuel and the surrounding gas to a temperature below the temperature at which soot is generated, and therefore no more soot is generated. In addition, the amount of NO _x generated at this time is about 10 ppm or less, and therefore the amount of NO _x generated becomes extremely small.

As the amount of injected fuel increases, the amount of heat generated at the time of combustion increases, so that to maintain the temperature of the fuel and the gas surrounding it at a temperature lower than the temperature at which soot is generated Amount of heat generated by the EGR gas must be increased. Therefore, as in 10 shown, the amount of EGR gas can be increased as the amount of injected fuel is increased. That is, the amount of EGR gas must be increased as the required engine load becomes higher.

On the other hand, in the engine load range (Z2) exceeds 10 the total amount of intake gas (X) needed to prevent soot generation, the total amount of intake gas (Y) that can be consumed. Therefore, in this case, it is necessary to reduce the total amount of intake gas (X) needed for preventing the soot generation in the combustion chamber 5 to provide an overload or a compression of both the EGR gas and the intake air or only the EGR gas to perform. When no load or compression of the EGR gas, etc. is performed in the engine load region (Z2), the total amount of the intake gas (X) corresponds to the total amount of the intake gas (Y) that can be taken. Therefore, in this case, in order to prevent the generation of soot, the amount of air is reduced slightly to increase the amount of EGR gas, and the fuel is made to burn at a stage where the air-fuel ratio is rich.

As explained above, shows 10 the case of combustion of fuel at the stoichiometric air / fuel ratio. In the operating range with low engine load (Z1), which is in 10 is shown, it is possible even if the amount of air below the in 10 is lowered, that is, even when providing a rich air / fuel ratio, to prevent the generation of soot and to cause an amount of NO _x generated of about 10 ppm or less. It is also in the low engine load (Z1) operating area, which is in 10 shown, possible, even if the amount of air over the in 10 is increased, that is, when providing a lean average air / fuel ratio of 17 to 18, to prevent the generation of soot and cause an amount of NO _x generated of about 10 ppm or less.

That is, when providing a rich air-fuel ratio, the fuel is in excess, but since the combustion temperature is lowered to a low temperature, the excess fuel does not turn into soot, and therefore no soot is generated. In addition, only a very small amount of NO _{x is} generated at this time. On the other hand, when the average air / fuel ratio is lean or when the air / fuel ratio is equal to the stoichiometric air / fuel ratio, a small amount of soot is generated as the combustion temperature increases, but the combustion temperature is lowered to a low temperature , and therefore no soot is generated at all. In addition, only a very small amount of NO _{x is} generated.

In this way, in the low engine load operating range (Z1), regardless of the air / fuel ratio, that is, whether a rich air / fuel ratio or the stoichiometric air / fuel ratio or an average lean air / fuel Ratio, no soot is generated, and the amount of NO _x generated becomes extremely small. Therefore, in view of the improvement of the fuel consumption rate, it can be said that it is preferable to make the average of the air-fuel ratio lean.

Incidentally, only when the engine load is relatively low and the amount of generated heat is small, the temperature of the fuel and the gas surrounding the fuel in the combustion can be lowered below a temperature at which the process of soot growth stops halfway. Therefore, in the embodiment of this invention in which the engine load is relatively low, the temperature of the fuel and the gas surrounding the fuel in the combustion is lowered below a temperature at which the process of soot growth stops midway and therefore becomes a first Combustion, ie a low-temperature combustion performed. When the engine load is relatively high, a second combustion, ie, normal combustion, is performed as usual. Here, as is apparent from the above explanation, the first combustion, ie, the low-temperature combustion, is a combustion in which the amount of inert gas in the combustion chamber is larger than the worst-case amount of inert gas that causes the maximum amount of generated soot, and therefore no soot is produced at all. The second combustion, ie normal combustion, is a combustion in which the amount of inert gas in the combustion chamber is less than the worst-case amount of inert gas.

11 shows a first operating range (I) in which the first combustion, ie, the low-temperature combustion is performed, and a second operating range (II) in which the second combustion, that is, the normal combustion is performed. In 11 the ordinate (L) shows the degree of depression of the accelerator pedal 40 ie the required engine load. The abscissa (N) shows the engine speed. Also shows in 11 X (N) a first boundary area between the first operating area (I) and the second operating area (II). Y (N) shows a second boundary area between the first operating area (I) and the second operating area (II). The decision to change from the first operating range (I) to the second operating range (II) is made on the basis of the first limit range X (N). The decision to change from the second operating range (II) to the first operating range (I) is made on the basis of the second limit range Y (N).

That is, when the operating state of the engine is the first operating region (I) and the low-temperature combustion is performed and if the required engine load (L) exceeds the first limit region X (N) which is a function of the engine speed (N), a decision is made in that the engine operating range changes to the second operating range (II), and therefore the normal combustion is performed. If thereafter the required engine load (L) falls below the second limit range Y (N) which is a function of the engine speed (N), it is judged that the engine operating range is changed to the first operating range (I), and therefore the low temperature combustion again becomes carried out.

12 shows the output of the sensor 21 for the air / fuel ratio. As in 12 As shown, the output current (I) of the sensor changes 21 for the air / fuel ratio according to the air / fuel ratio A / F. Accordingly, the air / fuel ratio of the output current (I) of the sensor 21 be derived for the air / fuel ratio. Now, with respect to 13 the engine operation control in the first operating range (I) and in the second operating range (II) is explained schematically.

13 shows the opening degree of the throttle valve 16 , the opening degree of the EGR control valve 23 , the EGR rate, the air / fuel ratio, the timing of the fuel injection, and the amount of injected fuel in relation to the required engine load (L). As in 13 is shown, in the first operating range (I), when the required engine load (L) is low, the throttle valve 16 gradually opened from the nearly fully closed state to the almost half-opened state while the required engine load (L) increases, and the EGR control valve 23 is gradually opened from the almost fully closed state to the fully open state while the required engine load (L) increases. At the in 13 In the embodiment shown, in the first operating range (I), an EGR rate of about 70 percent is effected, providing for a slightly lean air / fuel ratio therein.

In other words, in the first operating region (I), the opening degree of the throttle valve 16 and the EGR control valve 23 so controlled that the EGR rate becomes about 70% and the air / fuel ratio becomes a slightly lean air / fuel ratio. The air / fuel ratio at this time is controlled to the target air / fuel ratio bin, the opening degree of the EGR control valve 23 due to the output signal of the sensor 21 to correct for the air / fuel ratio. In the first operating range (Z), the fuel is injected before the compression dead center TDC. In this case, the fuel injection start timing (θS) is delayed as the required engine load (L) increases, and the fuel injection timing (θE) is retarded as the fuel injection start timing (θS) delays.

At idle, the throttle valve 16 closed until almost completely closed. At this time, the EGR control valve 23 also closed until almost completely closed. When the throttle valve 16 is closed to almost fully closed state, the pressure in the combustion chamber 5 lowered in the initial stage of the compression stroke and therefore the compression pressure decreases. When the compression pressure decreases, the compression power of the piston decreases 4 , and therefore the vibration of the motor housing decreases 1 , That is, idling becomes the throttle valve 16 closed to almost fully closed state, reducing the vibration of the motor housing 1 is restricted.

On the other hand, when the engine operating region changes from the first operating region (I) to the second operating region (II), the opening degree of the throttle valve increases 16 in a step of half open state to fully open state. Meanwhile, in the sinks in 13 In the embodiment shown, the EGR rate at once increases from about 70 percent to less than 40 percent, and the air / fuel ratio increases at once. That is, the EGR rate skips the range of the EGR rate ( 9 ) in which the large amount of smoke is generated, and therefore no large amount of smoke is generated when the engine operating range from the first operating range (I) to the second operating range (II) changes.

In the second operating range (II) normal combustion is carried out as usual. This combustion causes some generation of soot and NO _x . Their thermal efficiency, however, is higher than that of low temperature combustion. Therefore, as the engine operating range changes from the first operating range (I) to the second operating range (II), the amount of injected fuel decreases in one stage, as in FIG 13 shown.

In the second operating range (II), the throttle valve 16 kept in fully open condition, except in a part of it. The opening degree of the EGR control valve 23 decreases gradually as the required engine load (L) increases. In this operating range (II), the EGR rate decreases as the required engine load (L) increases, and the air / fuel ratio decreases as the required engine load (L) increases. However, a lean air / fuel ratio is made from the air / fuel ratio even if the required engine load (L) becomes high. In addition, in the second operating range (II), the fuel injection start timing (θS) is made close to the compression dead center TDC.

14 shows the air / fuel ratios A / F in the first operating range (I). In 14 the curves denoted by A / F = 15.5, A / F = 16, A / F = 17 and A / F = 18 respectively show the cases in which the air / fuel ratios are 15.5, 16, 17 and 18 were. The air / fuel ratio between two of these curves is defined by the proportional allocation. As in 14 In the first operating range (I), the air / fuel ratio is lean, and the leaner the air / fuel ratio is, the lower the required engine load (L) becomes.

That is, the amount of heat generated during combustion decreases as the required engine load (L) decreases. Therefore, even if the EGR rate decreases, as soon as the required engine load (L) decreases, the low-temperature combustion can be performed. As the EGR rate decreases, the air / fuel ratio becomes high. That's why, as in 14 shown, the air / fuel ratio A / F, when the required engine load (L) decreases. The higher the air / fuel ratio becomes, the more the fuel consumption improves. Accordingly, in the present embodiment, the air-fuel ratio A / F increases as the required engine load (L) decreases, so that the air-fuel ratio is made as lean as possible.

A target opening degree (ST) of the throttle valve 16 , which is needed to set the air / fuel ratio to the target air / fuel ratio in 14 is shown in the ROM 32 the electronic control unit 32 It stores a function of the required engine load (L) and the engine speed (N), which in 15 (A) is shown. A target opening degree (SE) of the EGR control valve 23 , which is needed to set the air / fuel ratio to the target air / fuel ratio in 14 is shown in the ROM 32 the electronic control unit, wherein it has a function of the required engine load (L) and the engine speed (N), in 15 (B) is shown.

16 FIG. 12 shows target air / fuel ratios when the second combustion, ie, normal combustion, is performed as usual. In 16 the curves denoted A / F = 24, A / F = 35, A / F = 45 and a / F = 60 respectively show the cases in which the target air / fuel ratios 24, 35, 45 and 60. A target opening degree (ST) of the throttle valve 16 , which is required to make the air / fuel ratio to the desired air / fuel ratio, is in the ROM 32 stored the electronic control unit, wherein it has a function of the required engine load (L) and the engine speed (N), in 17 (A) is shown. A target opening degree (SE) of the EGR control valve 23 , which is required to make the air / fuel ratio to the desired air / fuel ratio, is in the ROM 32 stored the electronic control unit, wherein it has a function of the required engine load (L) and the engine speed (N), in 17 (B) is shown.

Therefore, in the diesel engine of this embodiment, the first combustion, that is, the low-temperature combustion and the second combustion, that is, the normal combustion, change due to the degree of depression (L) of the accelerator pedal 40 and the engine speed (N). With each combustion, the opening degrees of the throttle valve 16 and the EGR control valve on the basis of the records given in the 15 and 17 are shown controlled.

18 is a plan view showing an apparatus for purifying the exhaust gas, and 19 is a side view of it. The device comprises a switching section 71 that with the downstream exhaust manifold 17 over an exhaust pipe 18 connected, a particle filter 70 , a first connecting portion 72a for connecting one side of the particulate filter 70 with the switching section 71 , a second connecting portion 72b for connecting the other side of the particulate filter 70 with the switching section 71 , and an exhaust pipe 73 at the downstream switching section 71 , The switching section 71 comprises a valve housing 71a , which regulates the flow of the exhaust gas in the change region 71 shuts off. The valve housing 71a is driven by a negative pressure drive, a stepping motor or the like. In a shut-off position of the valve housing 71a communicates the upstream side in the switching section 71 with the first connection section 72a and the downstream side thereof communicates with the second connection portion 72b , and therefore, the exhaust gas flows from the first side of the particulate filter 70 to the second page, as in 18 indicated by arrows.

20 shows a further shut-off position of the valve housing 71a , In this shut-off position, the upstream side communicates in the switching section 71 with the second connection section 72b and the downstream side in the switching section 71 communicates with the first connection section 72a , and therefore, the exhaust gas flows from the second side of the particulate filter 70 to the first page, as indicated by arrows in 20 displayed. Therefore, by switching the valve body 71a the direction of the exhaust gas entering the particle filter 70 can be reversed, that is, the side of the particulate filter at which the exhaust gas flows upward, and the side of the particulate filter, where the exhaust gas flows downward, can be reversed.

Therefore, this device for purifying the exhaust gas can reverse the side of the particulate filter, where the exhaust gas flows upward and the side of the particulate filter, where the exhaust gas flows downward, by a very simple construction. In addition, the particulate filter requires a large opening area to facilitate the introduction of the exhaust gas. In the apparatus, the particle filter can be used with a large opening area without its attachment to the vehicle causes difficulties, as in the 18 and 19 shown.

Also shows 21 a middle position of the valve housing 71a between the two shut-off positions. In the middle position, the switching section becomes 71 not locked. The exhaust gas does not flow through the particle filter 70 which has a higher resistance. That is, the exhaust gas bypasses the particle filter 70 and flows directly into the exhaust pipe, as indicated by the arrows in 21 shown. The valve housing 71a can be adjusted to any position other than this position by the stepping motor or the like. However, the valve housing is usually placed in one of the two shut-off positions and the particle filter is used.

22 shows the construction of the particle filter 70 , in which 22 (A) a front view of the particle filter 70 is and 22 (B) a side sectional view thereof. As shown in these figures, the particle filter has 70 an elliptical shape and represents, for example, the wall-flow type honeycomb structure consisting of a porous material such as cordierite, and has many spaces in the axial direction passing through many partitions 54 which extend in the axial direction, are separated. Each one of two adjacent spaces is with a shutter 53 on the side where the exhaust gas flows down, closed, and the other is with a closure 53 at the side on which the exhaust gas flows upward, closed. Therefore, one of the two adjacent spaces serves as an exhaust gas flow passage 50 and the other serves as an exhaust outflow channel 51 , whereby the exhaust gas is forced, the partition 54 to penetrate, as indicated by arrows in 22 (B) displayed. The particles contained in the exhaust are much smaller than the pores of the partition 54 but collide with this and become on the surface of the dividing wall 54 on the side where the exhaust gas flows upward and on the pore surfaces of the partition wall 54 retained. Therefore, every partition wall serves 54 as a trap for retaining the particles. In the present particulate filter, in order to oxidize and eliminate the retained particulates, an active oxygen release agent and a noble metal catalyst, which will be explained below, are formed on both sides of the surfaces of the partition wall 54 and preferably also on the pore surfaces of the partition 54 carried.

The active oxygen release agent releases active oxygen to promote the oxidation of the particles, and preferably captures and retains oxygen when there is an excess of oxygen in the environment, and releases the retained oxygen as active oxygen when the oxygen concentration in the atmosphere Environment drops.

Platinum Pt is usually used as the noble metal catalyst. As the active oxygen releasing agent, at least one element selected from the alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs and rubidium Rb, the alkaline earth metals such as barium Ba, calcium Ca and strontium Sr, the rare earth elements such as lanthanum La and yttrium Y, and the transition metals.

As the active oxygen releasing agent, an alkali metal or an alkaline earth metal having an ionization tendency stronger than that of calcium Ca is preferably used, that is, an alkali metal. H. Potassium K, Lithium Li, Cesium Cs, Rubidium Rb, Barium Ba or Strontium Sr.

Next, how the particles retained on the particulate filter are oxidized and eliminated by the particulate filter carrying such an active oxygen release agent will be explained, referring to the case where platinum Pt and potassium K are used. The particles are oxidized and removed in the same manner even if another noble metal and another alkali metal, alkaline earth metal, rare earth metal or transition metal is used.

In a diesel engine, the combustion usually takes place under a condition of excess air, and therefore the exhaust gas contains a large amount of excess air. That is, when the ratio of the air to the fuel introduced into the intake system and the combustion chamber is called an air-fuel ratio of the exhaust gas, the air-fuel ratio is lean. In addition, NO is generated in the combustion chamber, and therefore the exhaust gas contains NO. In addition, the fuel contains sulfur S, and sulfur S reacts with the oxygen in the combustion chamber, thereby forming SO ₂ . Accordingly, the exhaust gas containing excess oxygen, NO and SO _{2 flows} into the side of the particulate filter 70 in which the exhaust gas flows upwards.

The 23 (A) and 23 (B) are enlarged views showing the surface of the particle filter 70 , with which the exhaust gas comes into contact, represent schematically. In the 23 (A) and 23 (B) denotes the reference number 60 a platinum Pt particle and 61 refers to the active oxygen release agent containing potassium K.

As described above, the exhaust gas contains a large amount of excess oxygen. When the exhaust gas comes into contact with the exhaust gas contact surface of the particulate filter, oxygen O ₂ adheres to the platinum (Pt) surface in the form of O ₂ ^- or O ^2- as shown in ^FIG 23 (A) shown. On the other hand, NO in the exhaust gas reacts on the surface of platinum Pt with O ₂ ^- or O ^2- , thereby producing NO ₂ (2NO + O ₂ → 2NO ₂ ). Next, part of the generated NO ₂ is released in the active oxygen release agent 61 absorbed as it is oxidized on the platinum Pt, and diffuses in farm of nitric acid NO ₃ ^- in the active oxygen release agent 61 while it is combined with potassium K, whereby potassium nitrate KNO _{3 is} formed, as in 23 (A) shown. Therefore, in this embodiment, NO _x contained in the exhaust gas becomes in the particulate filter 70 can be reduced, and the amount thereof, which is discharged into the atmosphere, can be reduced, that is, the active oxygen release agent also serves as a NO _x absorbent.

In addition, the exhaust gas contains SO ₂ as described above, and SO ₂ is also released into the active oxygen releasing agent due to a mechanism similar to that of the NO case 61 absorbed. That is, as described above, oxygen O ₂ in the form of O ₂ ^- or O ^2- adheres to the surface of platinum (Pt), and SO ₂ in the exhaust gas reacts with O ₂ ^- or O ^2- on the surface of platinum ( Pt), producing SO ₃ . Next, part of the generated SO ₃ in the active oxygen release agent 61 absorbs while being oxidized on the platinum Pt, and diffuses in the form of sulfuric acid ion SO ₄ ^2- in the active oxygen release agent 61 while it is combined with potassium K, whereby potassium sulfate K ₂ SO ₄ ^{- is} formed. Therefore, potassium nitrate KNO ₃ and potassium sulfate K ₂ SO ₄ in the active oxygen release agent 61 generated.

The particles in the exhaust gas adhere to the surface of the active oxygen releasing agent 61 that on the particle filter 70 rests as with 62 in 23 (B) shown. At this time, the oxygen concentration falls on the surface of the active oxygen releasing agent 61 with which the particle 62 in contact, from. As the oxygen concentration drops, a difference in concentration to the active oxygen release agent arises 61 which has a high oxygen concentration, and therefore, oxygen tends to be active oxygen releasing agent 61 to the surface of the active oxygen releasing agent 61 to wander, with which the particle 62 in contact. As a result, potassium nitrate becomes KNO ₃ , which in the active oxygen release agent 61 was degraded to potassium K, oxygen O and NO degraded, with oxygen O to the surface of the active oxygen release agent 61 wanders, with which the particle 62 is in contact and NO becomes the active oxygen release agent 61 emitted to the outside. Outwardly emitted NO is oxidized on platinum (Pt) on the downstream side, and again becomes active oxygen release agent 61 absorbed.

At this time, potassium sulfate K ₂ SO ₄ , which is active in the active oxygen release agent, also becomes active 61 was degraded to potassium K, oxygen O and SO ₂ degraded, with oxygen O to the surface of the active oxygen release agent 61 wanders, with which the particle 62 is in contact, and SO ₂ is emitted to the outside by the active oxygen releasing agent. SO ₂ emitted externally is oxidized on platinum Pt on the downstream side and becomes active oxygen release agent again 61 absorbed. Here However, the potassium sulfate K ₂ SO ₄ is stable and releases less active oxygen than potassium nitrate KNO ₃ .

On the other hand, the oxygen O is the surface of the active oxygen releasing agent 61 wanders, with which the particle 62 is in contact to one which has been degraded from such compounds as potassium nitrate KNO ₃ or potassium sulfate K ₂ SO ₄ . Oxygen released from the compound has a high level of energy and shows a very high activity. Therefore, the oxygen that comes to the surface of the active oxygen releasing agent 61 wanders, with which the particle 62 is in contact to active oxygen O. As soon as it comes in contact with active oxygen O, the particle becomes 62 oxidized without generating a flash for a short time, for example a few minutes or a few tens of minutes. In addition, active oxygen becomes oxidized to the particle 62 also released when NO and SO ₂ in the active oxygen release agent 61 are absorbed. That is, it can be considered that NO _x in the active oxygen release agent 61 in the form of nitric acid ions NO ₃ ^- diffuses, while it is combined with oxygen atoms and separated by an oxygen atom, and during which active oxygen is generated. The particles 62 are also oxidized by this active oxygen. In addition, the particles that are on the particle filter 70 Not only oxidized by active oxygen, but also by oxygen contained in the exhaust gas.

The higher the temperature of the particulate filter becomes, the more becomes the platinum Pt and the active oxygen release agent 61 activated. Therefore, the higher the temperature of the particulate filter becomes, the larger the amount of active oxygen O becomes, that of the active oxygen releasing agent 61 is released, per unit of time. In addition, the higher the temperature of the particles, the easier it is for the particles to naturally oxidize. Therefore, the amount of particles that can be oxidized and eliminated per unit time without generation of a luminous flame on the particulate filter increases, and at the same time there is an increase in the temperature of the particulate filter.

The solid line in 24 shows the amount of particles (G) which can be oxidized and eliminated per unit time without producing a luminous flame. In 24 the abscissa represents the temperature TF of the particulate filter. Here shows 24 the case where the time unit is 1 second, that is, the amount of particles (G) that can be oxidized and eliminated per 1 second. However, any times such as 1 minute, 10 minutes or the like may be selected as the time unit. For example, in the case where 10 minutes are used as a unit time, the amount of particles (O) that can be oxidized and removed per unit time represents the amount of particles (G) that can be oxidized and eliminated every 10 minutes. In the same case, the particle amount (G) which can be oxidized and eliminated without generating a luminous flame when the temperature of the particulate filter increases 70 rises, as in 24 shown. The amount of particles emitted from the combustion chamber per unit time is referred to as the amount of emitted particles (M). When the amount of the emitted particles (M) is smaller than the amount of particles (G) that can be oxidized and eliminated, for example, if the amount of emitted particles (M) per 1 second is smaller than the amount of particles (G) per 1 Can be oxidized and eliminated, or the amount of emitted particles (M) per 10 minutes is smaller than the amount of particles (G) which can be oxidized and eliminated per 10 minutes, that is, in the range (I) of 24 is located, the particles that are emitted from the combustion chamber, all oxidized and eliminated one after the other, without producing a luminous flame on the particle filter for a short time.

On the other hand, when the amount of emitted particles (M) is larger than the amount of particles (G) that can be oxidized and eliminated, that is, in the range (II) of 24 The amount of active oxygen is insufficient to oxidize and remove all particles sequentially. The 25 (A) to (C) show how the particles are oxidized in such a case.

That is, in the case when the amount of active oxygen is insufficient to oxidize all the particles, when the particles 62 on the active oxygen release agent 62 adhere, only a part of the particles oxidizes, as in 25 (A) and the other part of the particle which has not been sufficiently oxidized remains on the surface of the particulate filter where the exhaust gas flows upward. When the state of lack of active oxygen is stopped, a part of the particles which have not been oxidized sequentially remains on the surface of the particulate filter where the exhaust gas flows upward. As a result, the surface of the particulate filter, where the exhaust gas flows upward, with the remaining ponds 63 covered, as in 25 (B) shown.

The remaining particles 63 gradually convert to carbonaceous substances that can hardly be oxidized. In addition, when the surface of the particulate filter, where the exhaust gas flows upward, with the remaining particles 63 is covered, the platinum (Pt) on the oxidation of NO and SO ₂ and the active oxygen precipitating agent 61 hindered in the release of active oxygen. The remaining particles 63 can gradually over a relative oxidized over a long period of time. However, store as in 25 (C) shown, other particles 64 one by one to the remaining particles 63 and when the deposited particles form a layer, these particles, even if they are easily oxidizable particles, can not be oxidized since these particles are separated from platinum (Pt) or the active oxygen release agent. Accordingly, other particles gradually deposit on these particles 64 at. That is, when the state in which the amount of emitted particles (M) is larger than the amount of particles (G) that can be oxidized and removed, the settled particles form a layer on the particle filter.

Therefore, in the range (I) of 24 the particles are oxidized and eliminated without forming a luminous flame for a short time in order to 11 ) from 24 the settled particles form a layer on the particle filter. Therefore, the settling of particles on the particulate filter can be prevented when the relationship between the amount of emitted particulates (M) and the amount of particulates which can be oxidized and eliminated (G) is in the range (I). As a result, the pressure loss of the exhaust gas in the particulate filter hardly changes and is maintained at a minimum pressure loss value which is almost constant. Therefore, the decrease in engine power can be kept as low as possible. However, this is not always done and the particles can settle on the particulate filter if nothing is done.

In order to prevent the particles from settling on the particulate filter, in this embodiment, the above control unit controls 30 the degree of opening of the valve body 71a according to a first flowchart, which is in 26 is shown. This flowchart is repeated at fixed intervals. At stage 101 a temperature (TF) of the particulate filter is determined. In this determination, a temperature sensor is mounted on the particulate filter and determines the temperature of the particulate filter directly. In addition, the temperature of the particulate filter at predetermined time intervals can be calculated based on the amount of exhaust gas flowing into the particulate filter at engine start and its temperature. Next, the current operating condition of the engine is determined by looking at the engine load sensor 41 , the crank angle sensor 42 and the like. In the case of the diesel engine of this embodiment, it is also determined which of the two burns was selected. When the operating condition of the engine has been determined, the amount of exhaust gas, the temperature of the exhaust gas, the oxygen concentration in the exhaust gas, the amount of the emitted particulates, and the like can be estimated.

Next, at step 103 the currently required amount of particles that can be oxidized and removed can be calculated based on the oxygen concentration in the exhaust gas, the amount of emitted particles, and the like. In addition, the lowest temperature (TFt) of the particulate filter that causes this amount of particulates to be oxidized and removed is calculated. At step 104 the amount of temperature change (dTF) of the particulate filter is calculated based on the instantaneous temperature (TF) of the particulate filter, the instantaneous amount of exhaust gas, the instantaneous temperature of the exhaust gas, and the like.

Next, at step 105 the amount of temperature change (dTF) adds to the instantaneous temperature (TF) of the particulate filter, and it is determined whether the result is greater than the lowest temperature (TFt). For example, if the instantaneous temperature (TF) of the particulate filter is very high, even if the instantaneous temperature of the exhaust gas is lower than this temperature (TF), so that the temperature of the particulate filter is lowered, the result in step 105 be positive. If the result at step 105 is positive, no problems arise. Accordingly, the valve housing remains 71a in a shut-off position and the routine is stopped.

If the result at step 105 however, if it is negative and nothing is done, the particles settle on the particle filter and it becomes difficult to oxidize and eliminate them. To prevent this, the exhaust gas is caused not to flow through the particulate filter, but to bypass it. At step 106 the amount of diverted exhaust gas is calculated. The lowest temperature (TFt) and the amount of temperature change (dTF) in the steps 103 and 104 apply in the event that the entire amount of exhaust gas flows into the particle filter. For example, when only half the amount of exhaust gas flows in the particulate filter, the amount of the emitted particulates (M), that is, the amount of particulates flowing into the particulate filter decreases by half, and therefore the required lowest temperature (TFt) may be lower. In addition, when the temperature of the exhaust gas is lower than the instantaneous temperature (TF) of the particulate filter, the amount of the temperature change (dTF) becomes a minus value. Their absolute value can be kept small. Therefore, when the temperature of the exhaust gas is lower than the instantaneous temperature (TF) of the particulate filter and the result at step 105 without a large difference being negative, the valve housing becomes a suitable opening degree between the current shut-off position and the middle position of step 107 emotional. Thus, only the amount of exhaust gas that is at step 106 has been calculated, causes the particle filter to bypass and settling of particles on it is prevented.

Of course, when the temperature of the exhaust gas is very low, the valve housing 71a moved to the center position to prevent a decrease in the temperature of the particulate filter, and therefore, the entire exhaust gas is caused to bypass the particulate filter. Incidentally, the currently required amount of particles that is at step 103 oxidized and eliminated, not always equal to the instantaneous amount of emitted particles. For example, when fuel is no longer supplied during braking of the engine and the like, the amount of emitted particles becomes practically zero. However, if at this time the required amount of particulate that can be oxidized and removed becomes zero and the lowest temperature (TFt) drops below 100 ° C (see 24 ), so that the temperature of the particulate filter actually drops below 100 ° C, the temperature of the particulate filter at the next engine acceleration can not rise immediately, and therefore, not all particles can be oxidized. Accordingly, it is preferable that the required amount of particulate which can be oxidized and eliminated is always more than a predetermined amount, that is, the lowest temperature (TFt) of the particulate filter does not fall below, for example, 200 ° C.

Incidentally, depending on the operating condition of the engine, the amount of the emitted particulates increases, and thus the result is step 105 negative. At this time, when a part of the exhaust gas is caused to bypass the particulate filter, the amount of the emitted particulates, that is, the amount of the particulates flowing into the particulate filter can be reduced, and thus the settling of particulates on the particulate filter can be prevented become.

27 FIG. 12 is a second flowchart that is performed in place of the first flowchart to prevent settling of particulates on the particulate filter. This will be explained below. This flowchart is repeated at fixed intervals. First, at step 201 determines whether the current amount of injected fuel (TAU) is less than the set amount (TAU1). If the result is negative, the amount of injected fuel (TAU) is relatively large and therefore the temperature of the exhaust gas increases. Therefore, since the temperature of the particulate filter does not drop much, the valve body becomes 71a held in a shut-off position and the routine is aborted.

On the other hand, if the result of step 201 is negative, the temperature of the exhaust gas below a predetermined temperature. Therefore, when all the exhaust gas passes through the particulate filter, the temperature of the particulate filter drops considerably, and therefore, the amount of the particulate which can be oxidized and removed considerably decreases. Accordingly, the amount of the bypassed exhaust gas is calculated so that the lower the temperature of the exhaust gas or the smaller the amount of injected fuel, the larger the amount of exhaust gas that does not flow through the particulate filter but bypasses it. At step 203 becomes the opening degree of the valve body 71a set between a shut-off position and the center position due to this amount of the bypassed gas.

Therefore, for example, during an interruption of the fuel supply, in which the temperature of the exhaust gas is very low, the entire exhaust gas is caused to bypass the particulate filter. If the temperature of the exhaust gas is not very low, a portion of the exhaust gas is caused to bypass the particulate filter. Accordingly, the temperature of the particulate filter is prevented from greatly decreasing, and therefore, the amount of the particulate which can be oxidized and eliminated on the particulate filter remains relatively high, and settling of particulates on the particulate filter can be prevented.

Of course, in this flowchart, if the result at step 201 is negative, the entire exhaust gas are caused to bypass the particle filter in order to prevent lowering of the temperature of the particulate filter with certainty. The control of this flowchart is less precise than that of the first flowchart. However, it is very simple and does not require complicated calculations. In addition, at step 201 determining whether the driver depresses the accelerator pedal instead of determining the amount of fuel injected. At this time, an interruption of the fuel supply is performed so that all the exhaust gas can be made to bypass the particulate filter. In addition, it is determined, for example, whether the driver releases the accelerator pedal during the stop of the car and the engine is idling at this time, so that the amount of injected fuel is low. Therefore, all or part of the exhaust gas may be caused to bypass the particulate filter.

If the exhaust gas of the first or second flow scheme is caused to bypass the particulate filter, if the particulates remain on the partition wall of the particulate filter, no other particulate matters will be deposited on the remaining particulates as the exhaust gas is diverted. Therefore, the residual particles of active oxygen released from the active oxygen releasing agent at the partition wall can be gradually oxidized and eliminated. The amount of active oxygen released from the active oxygen is limited, and therefore the active oxygen release agent can not re-release active oxygen after releasing active oxygen, thereby oxidizing and eliminating the particles, if it does not produce oxygen the environment absorbed as above described. When all the exhaust gas bypasses the filter, no new oxygen is supplied to the environment of the particulate filter bulkhead, and therefore the absorbed and released oxygen on the active oxygen release agent becomes inactive due to the lack of oxygen. Therefore, the remaining particles may not be completely oxidized and eliminated. In addition, the particles which have no contact with the active oxygen releasing agent on the partition wall of the particulate filter are difficult to be oxidized due to the oxygen deficiency. Accordingly, when the exhaust gas is caused to bypass the particulate filter due to the first or second flowchart, it is preferable that all of the exhaust gas is not caused to bypass the particulate filter so that at least a part of the exhaust gas flows through the particulate filter. However, this does not always have to be done. Thus, no oxygen deficiency occurs in the vicinity of the partition wall of the particulate filter.

29 Fig. 10 is a plan view showing another embodiment of the exhaust gas purifying apparatus. A difference to in 18 shown device is that the oxygen supply units 74a and 74b for the oxygen supply with the first connection section 72a or with the second connection section 74b to be provided. According to this embodiment, when a part of the exhaust gas bypasses the particulate filter, as mentioned above, oxygen may be introduced into one of the connecting portions 72a or 72b which is located on the side where the exhaust gas flows upwards. Therefore, the oxygen deficiency in the vicinity of the partition wall of the particulate filter is surely prevented, and therefore, the remaining particulates on the partition wall of the particulate filter can be surely oxidized and removed while the exhaust gas is being diverted.

30 Fig. 10 is a plan view showing another embodiment of the exhaust gas purifying apparatus. A difference to the in 18 shown device is that the reducing agent supply units 75a and 75b which can supply a reducing agent such as fuel in a large area to both sides of the particulate filter can be provided. According to this embodiment, when a part of the exhaust gas flows through the particulate filter as mentioned above, the reducing agent may be led to the side of the particulate filter where the exhaust gas is sucked. Therefore, the supplied reducing agent is sufficiently burned by the oxidation catalyst platinum (Pt), which rests on the partition wall of the particulate filter, without oxygen deficiency. The heat of combustion therefrom not only increases the temperature in the exhaust gas inlet portion of the particulate filter, but also the temperature in the exhaust gas outlet portion with the exhaust gas flowing therethrough. Therefore, the temperature of the whole particulate filter is increased, so that the amount of particulates that can be oxidized and removed at the partition wall of the particulate filter, and thus the particles remaining on the partition wall of the particulate filter can be oxidized and eliminated with certainty while the exhaust gas is being diverted. In this embodiment, the reducing agent supply units direct the reducing agent directly into the particulate filter, and therefore, no unnecessary reducing agent is applied to the inner wall of the connecting portions 72a . 72b and the like, is supplied, and the amount of the reducing agent can be restricted to a minimum.

In addition, in the first and second flowcharts, the exhaust gas that does not flow through the particulate filter is temporarily released into the atmosphere. At this time, however, in the first flowchart, except when the amount of the emitted particulates is large at the specific engine operating condition, the temperature of the exhaust gas is usually low, that is, the exhaust gas temperature. H. the amount of injected fuel is low and the amount of emitted particles is low. Therefore, there are no big problems.

Incidentally, in the wall-flow type particle filter used in this embodiment, the particles collide with the surface of the partition wall 54 at which the exhaust gas flows upward, and with the surface opposite to the exhaust gas in the pores therein, that is, with one of the trapping surfaces of the partition wall 54 , and are detained there. If the amount of active oxygen released from one of the capture surfaces is insufficient for the retained particles, not all the retained particles are oxidized and eliminated, and a portion remains. Although, according to the first and second flowcharts, such residual particles are hardly generated, for some reason particles may remain on one of the trapping surfaces of the partition wall, as in FIG 28 (A) shown. The valve housing 71a in the switching section 71 may be in one of the two shut-off positions, and therefore, the side of the particulate filter where the exhaust gas flows upward and the side where the exhaust gas flows downward may be changed. Therefore, if the valve body 71a changes to another shut-off position after the valve body 71a was brought from one of the shut-off positions in the vicinity of the center position, the remaining particles and the settled particles are oxidized and removed.

Since no other particles settle back on the remaining particles on one of the capture surfaces of the partition, as the side of the particulate filter, where the exhaust gas upwards When the gas flows, and the side where the exhaust gas flows downward, the remaining particles are gradually oxidized and removed by active oxygen released from one of the trapping surfaces. In addition, particularly, the particles remaining in the pores in the partition wall are easily crushed by the exhaust gas flowing in the opposite direction into small pieces as in FIG 28 (B) shown, and they usually wander through the pore to the side of the downward flow.

Accordingly, many of the particles which have been crushed into small pieces diffuse into the pores of the partition wall, and they come into direct contact with the active oxygen release agent, which rests on the pore surface, and are oxidized and eliminated. Therefore, if the active oxygen release agent also rests on the pore surfaces in the bulkhead, the remaining particles can be oxidized and eliminated very easily. On the other capture surface, which is now on the side of the upward flow, since the exhaust gas flow has been reversed, ie on the surface of the dividing wall 54 where the exhaust gas flows upwards and at the surface opposite to the exhaust gas in the pores thereof on which the exhaust gas mainly impinges (from the opposite side of one of the trapping surfaces), the particulates in the exhaust gas adhere again and become active oxygen, that of the releasing agent released for active oxygen, oxidized and eliminated. In this oxidation, a part of the active oxygen released from the active oxygen releasing agent on the other trapping surface migrates with the exhaust gas to the downstream side, and is caused to still move the particles on one side in spite of the reversal of the exhaust gas flow the capture surfaces are oxidized and eliminated.

That is, the residual particles on one of the capture surfaces are exposed not only to active oxygen released from this capture surface, but also to the remainder of the active oxygen used to oxidize and remove the particles on the other capture surface, since the stream the exhaust gas is reversed. Therefore, if the particles are restrained by alternately using the one trapping surface and the other trapping surface of the partition wall of the particulate filter to reverse the side of the particulate filter at which the exhaust gas flows upward and the side where the exhaust gas flows downward When some particles settle as a layer on one of the trapping surfaces of the particulate filter, when the exhaust gas flow is reversed, active oxygen is added to the sedimented particles, and due to the reverse flow of the exhaust gas, no particles are deposited on the sedimented particles, and therefore the sedimented particles are deposited Particles are gradually oxidized and removed, and they can be sufficiently oxidized and removed for a while until the next time the exhaust gas is reversed. Of course, by alternately using the one capture surface and the other capture surface of the septum, the amount of retained particles on each capture surface is smaller than for a particulate filter where the same capture surface always traps the particles. This facilitates the oxidation and removal of the retained particles on the capture surface.

In addition, when the air-fuel ratio of the exhaust gas is made rich, that is, when the oxygen concentration in the exhaust gas is lowered, active oxygen O is suddenly released from the active oxygen releasing agent 61 emitted to the outside. Therefore, from the settled particles, those which can be easily oxidized due to the large amount of active oxygen released at one time, and they can be oxidized and removed from the same without the luminous flame.

On the other hand, if the air-fuel ratio is kept lean, the surface of the platinum (Pt) is covered with oxygen, that is, oxygen contamination is caused. When such oxygen contamination is caused, the oxidation effect on the NO _x by the platinum (Pt) decreases, and therefore the absorption efficiency of the NO _x decreases. Therefore, the amount of active oxygen released from the active oxygen release agent decreases. However, when the air-fuel ratio is made rich, oxygen is consumed on the surface of the platinum Pt, and therefore the oxygen contamination ceases. Accordingly, when the air / fuel ratio again changes from rich to lean, the oxidation effect on the NO _x becomes strong, and therefore the efficiency of absorption increases. Therefore, the amount of active oxygen that increases from the active oxygen precipitating agent increases 61 is released.

Therefore, if the air-fuel ratio is kept lean, as the air-fuel ratio changes from lean to rich now and then, the oxygen contamination of the platinum (Pt) every time stops, and therefore, the amount of released active oxygen increases when the air / fuel ratio is lean. Therefore, the oxidation process of the particle on the particle filter 70 be encouraged.

In addition, the termination of the oxygen contamination causes combustion of the reducing agent and the heat of combustion thereof increases the temperature of the particulate filter. Therefore, the amount of particles that can be oxidized and eliminated by the particulate filter increases, and therefore, the settled particles are more easily oxidized and eliminated. When the air / fuel ratio in the exhaust is made rich when the upstream side and the downstream side of the particulate filter from the valve housing 71a vice versa, or immediately thereafter, the other capture surface, on which no particles remain or settle, can release a greater amount of active oxygen. Therefore, the larger amount of released active oxygen can oxidize and eliminate the remaining and settled particles with greater certainty.

As a method to make the air-fuel ratio rich, for example, the above-mentioned low-temperature combustion may be performed. Of course, when changing from the normal combustion to the low-temperature combustion or before, the side of the particulate filter where the exhaust gas flows upward and the side where the exhaust gas flows downward may be reversed. As mentioned above, the low temperature combustion is performed on the low engine load side, and therefore, the low temperature combustion is often performed immediately after the engine braking fuel supply throttling. Therefore, immediately after the valve body 71a was brought into the middle position, often performed a low-temperature combustion. In addition, by supplying reducing agent through the above-mentioned reducing agent supply units, the exhaust gas air-fuel ratio can be made rich. In addition, in order to make the air-fuel ratio of the exhaust rich, only the combustion air-fuel ratio can be made rich. In addition, in addition to the main fuel injection in the compression stroke, the exhaust stroke, or the expansion stroke, the fuel injector may inject fuel into the cylinder (post-injection) or inject fuel into the cylinder in the intake stroke (pre-injection). Of course, it is possible that there is no break between the post-injection or the pre-injection and the main fuel injection. In addition, fuel can be supplied to the exhaust system.

In addition, when the side of the particulate filter at which the exhaust gas flows upward and the side where the exhaust gas flows downward are reversed, even if a large amount of particulates has settled on one of the trapping surfaces of the particulate filter, the settled particles will pass through Inverted exhaust stream easily smashed into small pieces. Some of the particles which can not be oxidized and removed in the pores of the partition wall are removed by the particle filter. However, therefore, it is avoided that the exhaust resistance of the particulate filter increases more, which would have a detrimental effect on the vehicle operation, and that the large amount of sedimented particles ignites and burns at once, whereby the particulate filter would melt due to the heat. In addition, the other capture surface of the particle filter bulkhead may again retain particles.

Incidentally, when SO ₃ is present, calcium (Ca) in the exhaust gas forms calcium sulfate (CaSO ₄ ) in the form of ash. In order to prevent clogging of the meshes of the particulate filter with calcium sulfate CaSO ₄ , an alkali metal or an alkaline earth metal having a ionization tendency stronger than calcium (Ca), for example, potassium (K), as an active oxygen releasing agent may be used 61 be used. Therefore, SO ₃ , which is in the active oxygen release agent 61 is combined with potassium (K) to form potassium sulfate (K ₂ SO ₄ ), and therefore calcium (Ca) is not combined with SO ₃ but permeates the partition walls of the particulate filter. Accordingly, the meshes of the particulate filter are not clogged with ash. Therefore, it is desirable as an active oxygen release agent 61 to use an alkali metal or an alkaline earth metal having a stronger ionization tendency than calcium (Ca), for example potassium (K), lithium (Li), cesium (Cs), rubidium (Rb), barium (Ba) or strontium (Sr).

Even if only a noble metal such as platinum (Pt) rests on the particle filter, active oxygen can be released from the NO ₂ or SO ₃ trapped on the surface of platinum (Pt). In this case, however, a curve representing the amount of particles which can be oxidized and eliminated (G) is shifted slightly to the right, compared to the solid curve shown in FIG 24 is shown. In addition, cerium can be used as the active oxygen release agent. The cerium absorbs oxygen when the oxygen concentration is high (Ce ₂ O ₃ → 2CeO ₂ ) and releases active oxygen as the oxygen concentration decreases (2CeO ₂ → Ce ₂ O ₃ ). Therefore, in order to oxidize and eliminate the particles, the air-fuel ratio of the exhaust gas must be made rich at regular or irregular intervals. Instead of cerium, iron (Fe) or tin (Sn) can be used as the active oxygen release agent.

It is also possible to use an NO _x absorbent for purifying NO _x as the active oxygen releasing agent. In this case, the exhaust gas air-fuel ratio must at least temporarily be made rich to release and reduce the absorbed NO _x and SO _x . It is desirable to make the air-fuel ratio rich after the upstream side and the downstream side have been reversed.

Therefore, it is desirable that the upstream side and the downstream side of the particulate filter be reversed. However, this does not limit the present invention. Part of the exhaust gas or all of the exhaust gas may be caused to bypass the particulate filter by using a bypass line which is the side of the particulate filter at which the flow is directed upwards, with the side at which the flow is directed downwards to communicate as needed. In addition, the diesel engine of this embodiment can switch between the low-temperature combustion and the normal combustion. This does not limit the present invention. Of course, the present invention can also be applied to a diesel engine that performs only the normal combustion, or a gasoline engine that emits particulate matter.

In this embodiment, the particle filter itself carries the active oxygen release agent and active oxygen released from the active oxygen release agent, oxidizes and eliminates the particles. However, this does not limit the present invention. For example, a particulate oxidation material, such as active oxygen and NO ₂ , which acts as well as active oxygen may be released from a particulate filter or material that rests on it, or may flow into it from outside the particulate filter. In the case that the particle oxidation material flows into the particle filter from outside the particle filter, when the first capture surface and the second capture surface of the partition are alternately used to retain the particles, on a capture surface which is now on the side, at which the exhaust gas flows down, no more particles settle on the remaining particles and the remaining particles are completely oxidized and eliminated after a certain time. During this period of time, the other capture surface can retain the particles and the retained particles are oxidized and removed by the particulate oxidation material on the other capture surface. Thus, the same effects as mentioned above can be achieved. Of course, in this case, as the temperature of the particulate filter increases, the temperature of the particulates themselves increases, and hence their oxidation and elimination can be facilitated.

Although the invention has been described with reference to specific embodiments thereof, it should be understood that numerous modifications thereof may be made by one skilled in the art without departing from the spirit and scope of the invention.

Claims (10)

An apparatus for purifying the exhaust gas of an internal combustion engine, comprising a particulate filter disposed in the exhaust system on which the retained particulates are oxidized, and a bypass conduit through which the exhaust gas can bypass the particulate filter, the particulate filter oxidizing a predetermined amount of particulate matter depending on the temperature of the particulate filter and when an amount of injected fuel is less than a predetermined amount, a portion of the exhaust gas is caused to bypass the bypass passage, wherein the amount of bypassed exhaust gas is determined based on the amount of injected fuel. An apparatus for purifying the exhaust gas of an internal combustion engine according to claim 1, wherein the particulate filter carries an active oxygen release agent, and active oxygen released from the active oxygen release agent oxidizes the retained particulate on the particulate filter. An apparatus for purifying the exhaust gas of an internal combustion engine according to claim 2, wherein the active oxygen release agent receives and holds oxygen when there is excess oxygen in the environment and releases the trapped oxygen as active oxygen as the concentration of oxygen in the environment decreases. An apparatus for purifying the exhaust gas of an internal combustion engine, comprising an exhaust gas arranged particulate filter on which the retained particles are oxidized, and a bypass line through which the exhaust gas can bypass the particulate filter, wherein the particulate filter carries an active oxygen release agent, active oxygen was released from the release agent for active oxygen, the retained particles on the particulate filter is oxidized, holding the release agent for active oxygen NO _x to combine the NO _x with oxygen when an excess of oxygen in the surroundings is present, and the combined NO _x / oxygen liberates to degrade it to NO _x and active oxygen when the oxygen concentration in the environment decreases, the particulate filter has a lot of particles depending on the Temperature of the particulate filter can be oxidized and removed, and if the amount of injected fuel is less than a predetermined amount, a portion of the exhaust gas is caused to take the detour through the bypass line, wherein the amount of bypassed exhaust gas based on the amount of injected Fuel is determined. An apparatus for purifying the exhaust gas of an internal combustion engine, comprising a particulate filter disposed in the exhaust system on which the retained particulates are oxidized and a bypass conduit through which the exhaust gas can bypass the particulate filter, the particulate filter having a quantity of particulate matter dependent on the temperature can be oxidized and removed, and when a temperature of the exhaust gas is lower than a predetermined temperature, a part of the exhaust gas is caused to take the detour through the bypass line, wherein the amount of the diverted exhaust gas is determined based on the temperature of the exhaust gas , An apparatus for purifying the exhaust gas of an internal combustion engine according to claim 5, wherein the particulate filter carries an active oxygen release agent, and active oxygen is released from the active oxygen release agent, which oxidizes retained particulates on the particulate filter. An apparatus for purifying the exhaust gas of an internal combustion engine according to claim 6, wherein the active oxygen release agent receives and holds oxygen when there is excess oxygen in the environment, and releases the trapped oxygen as active oxygen when the oxygen concentration in the environment decreases. An apparatus for purifying the exhaust gas of an internal combustion engine, comprising an exhaust gas arranged particulate filter on which the retained particles are oxidized, and a bypass line through which the exhaust gas can bypass the particulate filter, wherein the particulate filter carries an active oxygen release agent, active oxygen was released from the release agent for active oxygen, the retained particles on the particulate filter is oxidized, holding the release agent for active oxygen NO _x to combine the NO _x with oxygen when an excess of oxygen in the surroundings is present, and releases combined NO _x / oxygen, whereby it degrades to active oxygen and NO _x as the oxygen concentration in the environment decreases, the particulate filter has an amount of particulates that can be oxidized and removed depending on the temperature of the particulate filter, and when an exhaust gas temperature is lower than s a predetermined temperature, a portion of the exhaust gas is caused to take the detour through the bypass line, wherein the amount of the bypassed exhaust gas is determined based on the temperature of the exhaust gas. An apparatus for purifying the exhaust gas of an internal combustion engine according to any one of claims 1-8, wherein when a part of the exhaust gas is caused to bypass the bypass passage, oxygen is introduced into the particulate filter. An apparatus for purifying the exhaust gas of an internal combustion engine according to any one of claims 1-8, wherein the particulate filter has an oxidizing ability, and when a part of the exhaust gas is caused to take the detour through the bypass, a reducing agent is supplied to the particulate filter.

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