Exhaust Purification Device of Compression Ignition Type Internal Combustion Engine

Abstract

In an internal combustion engine, the engine is formed so that an output of an electric motor can be superposed on an output of the engine. In the engine exhaust passage upstream of the NO.sub.X storage catalyst, an SO.sub.X trap catalyst able to trap the SO.sub.X contained in the exhaust gas is arranged. When regenerating the SO.sub.X trap catalyst, the vehicle drive power from the engine and the vehicle drive power from the electric motor are adjusted so that the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst becomes less than a predetermined SO.sub.X concentration during the regeneration period.

Description

TECHNICAL FIELD

[0001] The present invention relates to an exhaust purification device of a compression ignition type internal combustion engine.

BACKGROUND ART

[0002] Known in the art is an internal combustion engine arranging in an engine exhaust passage an NO.sub.X storage catalyst storing NO.sub.X contained in exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releasing the stored NO.sub.X when the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich. In this internal combustion engine, NO.sub.X formed when burning fuel under a lean air-fuel ratio is stored in the NO.sub.X storage catalyst. On the other hand, as the NO.sub.X storage catalyst approaches saturation of the NO.sub.X storage ability, the air-fuel ratio of the exhaust gas is temporarily made rich, whereby NO.sub.X is released from the NO.sub.X storage catalyst and reduced.

[0003] However, fuel and lubrication oil contain sulfur. Therefore, the exhaust gas also contains SO.sub.X. This SO.sub.X is stored together with the NO.sub.X in the NO.sub.X storage catalyst. This SO.sub.X is not released from the NO.sub.X storage catalyst by just making the exhaust gas a rich air-fuel ratio. Therefore, the amount of SO.sub.X stored in the NO.sub.X storage catalyst gradually increases. As a result, the storable NO.sub.X amount ends up gradually decreasing.

[0004] However, in this case, if raising the temperature of the NO.sub.X storage catalyst and making the air-fuel ratio of the exhaust gas flowing into the NO.sub.X storage catalyst rich, the SO.sub.X stored in the NO.sub.X storage catalyst is gradually released from the NO.sub.X storage catalyst. Therefore, there is known a hybrid internal combustion engine provided with an electric motor, in which when SO.sub.X should be released from the NO.sub.X storage catalyst, the air-fuel ratio of the exhaust gas is made rich and a speed of rotation of a crankshaft is made faster by the electric motor at the time of the expansion stroke to make an after-burn period longer and thereby make the exhaust gas temperature higher (for example, see Japanese Patent Publication (A) No. 2005-61234).

[0005] On the other hand, there is known an internal combustion engine in which an SO.sub.X trap catalyst able to trap the SO.sub.X in the exhaust gas is arranged in the engine exhaust passage upstream of the NO.sub.X storage catalyst (see Japanese Patent Publication (A) No. 2005-133610). In this internal combustion engine, by trapping the SO.sub.X contained in the exhaust gas by the SO.sub.X trap catalyst, the inflow of SO.sub.X into the NO.sub.X storage catalyst is prevented.

[0006] However, even when using such an SO.sub.X trap catalyst, when the SO.sub.X trap rate of the SO.sub.X trap catalyst falls, it is necessary to regenerate the SO.sub.X trap catalyst. In this case, the SO.sub.X trap catalyst can be regenerated by raising the temperature of the SO.sub.X trap catalyst. However, the amount of SO.sub.X trapped by this SO.sub.X trap catalyst is much greater than the amount of SO.sub.X stored in the NO.sub.X storage catalyst, and thus, if the SO.sub.X trap catalyst is excessively raised in temperature even a little, the trapped SO.sub.X is released all at once. As a result, the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst ends up becoming extremely high.

[0007] SO.sub.X is itself harmful, and if the temperature becomes higher, SO.sub.X sometimes changes to harmful hydrogen sulfide H.sub.2S. Therefore, it is necessary to avoid the concentration of SO.sub.X in the exhaust gas, which is exhausted into the outside air, from becoming high. That is, when using an SO.sub.X trap catalyst, it is necessary to hold the concentration of SO.sub.X in the exhaust gas flowing out from the SO.sub.X trap catalyst within a constant limit.

DISCLOSURE OF THE INVENTION

[0008] An object of the present invention is to provide a compression ignition type internal combustion engine able to hold the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst at a certain limit or lower.

[0009] According to the present invention, there is provided an exhaust purification device of compression ignition type internal combustion engine arranging, in an engine exhaust passage, an SO.sub.X trap catalyst able to trap SO.sub.X contained in exhaust gas and arranging, in the exhaust passage downstream of the SO.sub.X trap catalyst, an NO.sub.X storage catalyst storing NO.sub.X contained in the exhaust gas when the air-fuel ratio of an inflowing exhaust gas is lean and releasing stored NO.sub.X when the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich, wherein the device is provided with an electric power device able to generate vehicle drive power separate from the vehicle drive power from the engine and able to generate electric power from the engine and, when the SO.sub.X trap catalyst should be regenerated, the vehicle drive power from the engine and the vehicle drive power from the electric power device are adjusted so that an SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst becomes less than a predetermined SO.sub.X concentration during a regeneration period.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is an overview of a compression ignition type internal combustion engine, FIG. 2 is a cross-sectional view of the surface part of a catalyst carrier of an NO.sub.X storage catalyst, FIG. 3 is a cross-sectional view of the surface part of a substrate of an SO.sub.X trap catalyst, FIG. 4 is a view showing the SO.sub.X trap rate, FIG. 5 is a view showing a map of stored SO.sub.X amounts SOXA, SOXB, FIG. 6 is a view showing the relationship of the stored SO.sub.X amount .SIGMA.SOX and the stored SO.sub.X amount SO(n) for regeneration control, FIG. 7 is a flow chart for determining the timing of regeneration, FIG. 8 is a view showing the SO.sub.X release temperature, FIG. 9 is a time chart showing regeneration control, FIG. 10 is a view showing the output torque of the engine, FIG. 11 is a flow chart for regeneration control, FIG. 12 is a flow chart showing another embodiment for regeneration control, FIG. 13 is a time chart showing regeneration control, and FIG. 14 is a view showing another embodiment of an electric power device.

BEST MODE FOR CARRYING OUT THE INVENTION

[0011] FIG. 1 is an overview of a compression ignition type internal combustion engine.

[0012] Referring to FIG. 1, 1 indicates an engine body, 2 a combustion chamber of each cylinder, 3 an electronically controlled fuel injector injecting fuel into each combustion chamber 2, 4 an intake manifold, and 5 an exhaust manifold. The intake manifold 4 is connected through an intake duct 6 to the outlet of a compressor 7a of an exhaust turbocharger 7, while the inlet of the compressor 7a is connected through an intake air detector 8 to an air cleaner 9. Inside the intake duct 6, a throttle valve 10 driven by the step motor is arranged. Further, around the intake duct 6, a cooling device 11 for cooling the intake air flowing through the intake duct 6 is arranged. In the embodiment shown in FIG. 1, the engine cooling water is led into the cooling device 11 where the engine cooling water is used to cool the intake air.

[0013] On the other hand, the exhaust manifold 5 is connected to the inlet of an exhaust turbine 7b of the exhaust turbocharger 7. The outlet of the exhaust turbine 7b is connected to the inlet of a catalyst converter 12. Inside the catalyst converter 12, an SO.sub.X trap catalyst 13 and NO.sub.X storage catalyst 14 are arranged in this order from the upstream side. Inside the catalyst converter 12 between the SO.sub.X trap catalyst 13 and the NO.sub.X storage catalyst 14, a temperature sensor 15 for detecting the temperature of the exhaust gas flowing out from the SO.sub.X trap catalyst 13 and an SO.sub.X sensor 16 for detecting the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst 13 are provided. In the embodiment according to the present invention, the temperature of the SO.sub.X trap catalyst 13 is estimated from the detection value of this temperature sensor 15.

[0014] The exhaust manifold 5 and intake manifold 4 are connected to each other through an exhaust gas recirculation (hereinafter referred to as "EGR") passage 17. Inside the EGR passage 17, an electronic control type EGR control valve 18 is arranged. Further, around the EGR passage 17, a cooling device 19 for cooling the EGR gas flowing through the EGR passage 17 is arranged. In the embodiment shown in FIG. 1, engine cooling water is led to the cooling device 19 where the engine cooling water cools the EGR gas. On the other hand, each fuel injector 3 is connected through a fuel tube 20 to a common rail 21. This common rail 21 is fed with fuel from an electronically controlled variable discharge fuel pump 22. The fuel fed into the common rail 21 is fed through each fuel tube 20 into the fuel injectors 3. Further, inside the exhaust manifold 5, a reducing agent feed valve 23 for feeding a reducing agent comprised of for example a hydrocarbon into the exhaust manifold 5 is attached.

[0015] On the other hand, in the embodiment shown in FIG. 1, a transmission 25 is coupled with the output shaft of the engine, while an electric motor 27 is coupled with the output shaft 26 of the transmission 25. In this case, as the transmission 25, it is possible to use an ordinary gear-type automatic transmission provided with a torque converter, a manual transmission, a gear-type automatic transmission of a type designed to automatically perform the clutch operation and gear shift operation in a manual transmission provided with a clutch, etc.

[0016] Further, the electric motor 27 coupled with the output shaft 26 of the transmission 25 comprises an electric power device able to generate vehicle drive power separate from the vehicle drive power from the engine and able to generate electric power by the engine. In this embodiment shown in FIG. 1, this electric motor 27 comprises an AC synchronous motor provided with a rotor 28 attached on an output shaft 26 of the transmission 25 and attaching a plurality of permanent magnets to the outer circumference and a stator 29 provided with an excitation coil forming a rotary magnetic field. The excitation coil of the stator 29 is connected to a motor drive control circuit 30, while this motor drive control circuit 30 is connected to a battery 31 generating a DC high voltage.

[0017] The electronic control unit 40 is comprised of a digital computer and is provided with a ROM (read only memory) 42, RAM (random access memory) 43, CPU (microprocessor) 44, input port 45, and output port 46 which are connected to each other by a bi-directional bus 41. The output signals of the intake air detector 8, the temperature sensor 15 and the SO.sub.X sensor 16 are input through corresponding AD converters 47 to an input port 45. Further, the input port 45 receives as input various signals showing the gear of the transmission 25, the rotational speed of the output shaft 26, etc.

[0018] On the other hand, the accelerator pedal 32 is connected to a load sensor 33 generating an output voltage proportional to the amount of depression L of an accelerator pedal 32. The output voltage of the load sensor 33 is input through a corresponding AD converter 47 to the input port 45. Further, the input port 45 is connected to a crank angle sensor 34 generating an output pulse each time the crankshaft rotates by for example 10.degree.. On the other hand, the output port 46 is connected through a corresponding drive circuit 48 to the fuel injector 3, EGR control valve 18, the fuel pump 22, the reducing agent feed valve 23, transmission 25, motor drive control circuit 30, etc.

[0019] The feed of electric power from the electric motor 27 to the excitation coil of the stator 29 is normally stopped. At this time, the rotor 28 rotates together with the output shaft 26 of the transmission 25. On the other hand, when driving the electric motor 27, the DC high voltage of the battery 31 is converted at the motor drive control circuit 30 to a three-phase alternating current of a frequency of fm and a current value of Im, and this three-phase alternating current is fed to the excitation coil of the stator 29. This frequency fm is the frequency required for making the rotating magnetic field generated by the excitation coil rotate in synchronization with the rotation of the rotor 28. This frequency fm is calculated by a CPU 44 based on the rotational speed of the output shaft 26. At the motor drive control circuit 30, this frequency fm is made the frequency of the three-phase alternating current.

[0020] On the other hand, the output torque of the electric motor 27 is substantially proportional to the current value Im of the three-phase alternating current. This current value Im is calculated at the CPU 44 based on the required output torque of the electric motor 27. In the motor drive control circuit 30, this current value Im is made the current value of the three-phase alternating current.

[0021] Further, if driving the electric motor 27 by external force, the electric motor 27 operates as a generator. At this time, the generated electric power is recovered by the battery 31. Whether to use external force to drive the electric motor 27 is judged by the CPU 44. When it is judged that external force should be used to drive the electric motor 27, a motor control circuit 3 is used to control the electric motor 27 so that the generated electric power is recovered at the battery 31.

[0022] Next, the NO.sub.X storage catalyst 14 shown in FIG. 1 will be explained. This NO.sub.X storage catalyst 14 is comprised of a substrate on which for example a catalyst carrier comprised of alumina is carried. FIG. 2 illustrates the cross-section of the surface part of this catalyst carrier 60. As shown in FIG. 2, the catalyst carrier 60 carries a precious metal catalyst 61 diffused on the surface. Further, the catalyst carrier 60 is formed with a layer of an NO.sub.X absorbent 62 on its surface.

[0023] In the embodiment according to the present invention, as the precious metal catalyst 61, platinum Pt is used. As the ingredient forming the NO.sub.X absorbent 62, for example, at least one element selected from potassium K, sodium Na, cesium Cs, and other such alkali metals, barium Ba, calcium Ca, and other such alkali earths, lanthanum La, yttrium Y, and other rare earths is used.

[0024] If the ratio of the air and fuel (hydrocarbons) fed into the engine intake passage, combustion chamber 2, and exhaust passage upstream of the NO.sub.X storage catalyst 14 is called the "air-fuel ratio of the exhaust gas", an NO.sub.X absorption and release action such that the NO.sub.X absorbent 62 absorbs the NO.sub.X when the air-fuel ratio of the exhaust gas is lean and releases the absorbed NO.sub.X when the oxygen concentration in the exhaust gas falls is performed.

[0025] That is, explaining this taking as an example the case of using barium Ba as the ingredient forming the NO.sub.X absorbent 62, when the air-fuel ratio of the exhaust gas is lean, that is, the oxygen concentration in the exhaust gas is high, the NO contained in the exhaust gas, as shown in FIG. 2, is oxidized on the platinum Pt 61 to become NO.sub.2, next is absorbed in the NO.sub.X absorbent 62 and bonds with the barium oxide BaO to diffuse in the form of nitrate ions NO.sub.3-- into the NO.sub.X absorbent 52. In this way, NO.sub.X is absorbed in the NO.sub.X absorbent 62. So long as the oxygen concentration in the exhaust gas is high, NO.sub.2 is formed on the platinum Pt 61. So long as the NO.sub.X absorbent 62 is not saturated in NO.sub.X absorption ability, NO.sub.2 is absorbed in the NO.sub.X absorbent 62 and nitrate ions NO.sub.3.sup.- are formed.

[0026] As opposed to this, for example if the reducing agent feed valve 23 feeds the reducing agent to make the exhaust gas a rich air-fuel ratio or stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas falls, so the reaction proceeds in the reverse direction (NO.sub.3.sup.-.fwdarw.NO.sub.2), therefore the nitrate ions NO.sub.3 in the NO.sub.X absorbent 62 are released in the form of NO.sub.2 from the NO.sub.X absorbent 62. Next, the released NO.sub.X is reduced by the unburned HC and CO contained in the exhaust gas.

[0027] In this way, when the air-fuel ratio of the exhaust gas is lean, that is, when burning the fuel under a lean air-fuel ratio, the NO.sub.X in the exhaust gas is absorbed in the NO.sub.X absorbent 62. However, when the fuel continues to be burned under a lean air-fuel ratio, the NO.sub.X absorbent 62 eventually ends up becoming saturated in NO.sub.X absorption ability, therefore the NO.sub.X absorbent 62 ends up becoming unable to absorb the NO.sub.X. Therefore, in this embodiment of the present invention, before the NO.sub.X absorbent 62 becomes saturated in absorption ability, the reducing agent is fed from the reducing agent feed valve 23 to make the exhaust gas temporarily rich air-fuel ratio and thereby make the NO.sub.X absorbent 62 release the NO.sub.X.

[0028] On the other hand, the exhaust gas contains SO.sub.X, that is, SO.sub.2. If this SO.sub.2 flows into the NO.sub.X storage catalyst 14, this SO.sub.2 is oxidized on the platinum Pt 61 and becomes SO.sub.3. Next, this SO.sub.3 is absorbed in the NO.sub.X absorbent 62, bonds with the barium oxide BaO, is diffused in the form of sulfate ions SO.sub.4.sup.2- in the NO.sub.X absorbent 62, and forms stable sulfate BaSO.sub.4. However, the NO.sub.X absorbent 62 has a strong basicity, so this sulfate BaSO.sub.4 is stable and hard to break down. If just making the exhaust gas rich air-fuel ratio, the sulfate BaSO.sub.4 remains as is without breaking down. Therefore, in the NO.sub.X absorbent 62, the sulfate BaSO.sub.4 increases along with the elapse of time, therefore the NO.sub.X amount which the NO.sub.X absorbent 62 can absorb falls along with the elapse of time.

[0029] In this regard, in this case, if making the air-fuel ratio of the exhaust gas flowing into the NO.sub.X storage catalyst 14 rich in the state where the temperature of the NO.sub.X storage catalyst 14 is made to rise to the SO.sub.X release temperature of 600.degree. C. or more, the NO.sub.X absorbent 62 releases SO.sub.X. However, in this case, the NO.sub.X absorbent 62 only releases a little SO.sub.X at a time. Therefore, to make the NO.sub.X absorbent 62 release all of the absorbed SO.sub.X, it is necessary to make the air-fuel ratio rich over a long time, therefore there is the problem that a large amount of fuel or reducing agent becomes necessary.

[0030] Therefore, in an embodiment of the present invention, the SO.sub.X trap catalyst 13 is arranged upstream of the NO.sub.X storage catalyst 14 to trap the SO.sub.X contained in the exhaust gas by this SO.sub.X trap catalyst 13 and thereby prevent SO.sub.X from flowing into the NO.sub.X storage catalyst 14. Next this SO.sub.X trap catalyst 13 will be explained.

[0031] FIG. 3 illustrates the cross-section of the surface part of a substrate 65 of this SO.sub.X trap catalyst 13. As shown in FIG. 3, the substrate 65 is formed with a coat layer 66 on its surface. This coat layer 66 carries a precious metal catalyst 67 diffused on its surface. In the embodiment according to the present invention, as the precious metal catalyst 67, platinum is used. As the ingredient forming the coat layer 66, for example, at least one element selected from potassium K, sodium Na, cesium Cs, and other such alkali metals, barium Ba, calcium Ca, and other such alkali earths, lanthanum La, yttrium Y, and other rare earths is used. That is, the coat layer 66 of the SO.sub.X trap catalyst 13 exhibits a strong basicity.

[0032] Now, the SO.sub.X contained in the exhaust gas, that is, SO.sub.2, is oxidized on the platinum Pt 67 as shown in FIG. 3, then is trapped in the coat layer 66. That is, the SO.sub.2 diffuses in the form of sulfate ions SO.sub.4.sup.2- in the coat layer 66 to form a sulfate. Note that as explained above, the coat layer 66 exhibits a strong basicity. Therefore, as shown in FIG. 3, part of the SO.sub.2 contained in the exhaust gas is directly trapped in the coat layer 66.

[0033] In FIG. 3, the shading in the coat layer 66 shows the concentration of the trapped SO.sub.X. As will be understood from FIG. 3, the SO.sub.X concentration in the coat layer 66 is highest near the surface of the coat layer 66. The further in, the lower it becomes. If the SO.sub.X concentration near the surface of the coat layer 66 increases, the surface of the coat layer 66 weakens in basicity and the SO.sub.X trap ability weakens. Here, if the ratio of the amount of the SO.sub.X trapped in the SO.sub.X trap catalyst 13 to the amount of the SO.sub.X in the exhaust gas is called the "SO.sub.X trap rate", if the basicity of the surface of the coat layer 66 is weakened, the SO.sub.X trap rate falls along with that.

[0034] FIG. 4 shows the change along with time of the SO.sub.X trap rate. As shown in FIG. 4, the SO.sub.X trap rate is first close to about 100 percent, but rapidly falls as time elapses. Therefore, in the present invention, when the SO.sub.X trap rate falls below a predetermined rate, a temperature raising control for raising the temperature of the SO.sub.X trap catalyst 13 under a lean or rich exhaust gas air-fuel ratio is performed and thereby the SO.sub.X trap rate is restored.

[0035] For example, if raising the temperature of the SO.sub.X trap catalyst 13 when the exhaust gas air-fuel ratio is lean, the SO.sub.X present concentrated near the surface of the coat layer 66 diffuses toward the deep part of the coat layer 66 so that the concentration becomes uniform. That is, the nitrates formed in the coat layer 66 change from an unstable state where they concentrate near the surface of the coat layer 66 to the stable state where they are diffused evenly across the entire inside of the coat layer 66. If the SO.sub.X present near the surface of the coat layer 66 diffuses toward the deep part of the coat layer 66, the SO.sub.X concentration near the surface of the coat layer 66 falls. Therefore, when the temperature raising control of the SO.sub.X trap catalyst 13 has ended, the SO.sub.X trap rate is restored.

[0036] If making the temperature of the SO.sub.X trap catalyst 13 about 450.degree. C. when performing the temperature raising control of the SO.sub.X trap catalyst 13, it is possible to make the SO.sub.X present near the surface of the coat layer 66 diffuse in the coat layer 66. If raising the temperature of the SO.sub.X trap catalyst 13 to 600.degree. C. or so, the SO.sub.X concentration in the coat layer 66 can be made considerably even. Therefore, in this embodiment according to the present invention, at the time of temperature raising control of the SO.sub.X trap catalyst 13, the temperature of the SO.sub.X trap catalyst 13 is raised to 600.degree. C. or so and is held at 600.degree. C. or so.

[0037] On the other hand, even if making the air-fuel ratio of the exhaust gas flowing into the SO.sub.X trap catalyst 13 rich in the state raising the temperature of the SO.sub.X trap catalyst 13, the SO.sub.X trap rate can be restored. That is, if making the air-fuel ratio of the exhaust gas flowing into the SO.sub.X trap catalyst 13 in the state of raising the temperature of the SO.sub.X trap catalyst 13 rich, the trapped SO.sub.X is released from the SO.sub.X trap catalyst 13 and therefore the SO.sub.X trap rate is restored. Therefore, both when making the air-fuel ratio of the exhaust gas flowing into the SO.sub.X trap catalyst 13 lean and rich in the state raising the temperature of the SO.sub.X trap catalyst 13, the SO.sub.X trap rate can be restored.

[0038] Next, the timing of start of the action for regeneration of the SO.sub.X trap catalyst 13 for restoring the SO.sub.X trap rate will be explained.

[0039] In this embodiment according to the present invention, the SO.sub.X amount trapped by the SO.sub.X trap catalyst 13 is estimated. When the SO.sub.X amount trapped by the SO.sub.X trap catalyst 13 exceeds a predetermined amount, it is judged that the SO.sub.X trap rate has fallen below the predetermined rate. At this time, the action for regeneration of the SO.sub.X trap catalyst 13 for restoration of the SO.sub.X trap rate is started.

[0040] That is, fuel contains sulfur in a certain ratio. Therefore, the amount of SO.sub.X contained in the exhaust gas, that is, the amount of SO.sub.X trapped by the SO.sub.X trap catalyst 13, is proportional to the amount of fuel injection. The amount of fuel injection is a function of the required torque and engine speed. Therefore, the amount of SO.sub.X trapped by the SO.sub.X trap catalyst 13 becomes a function of the required torque and engine speed. In this embodiment according to the present invention, the SO.sub.X amount SOXA trapped per unit time in the SO.sub.X trap catalyst 13 is stored as a function of the required torque TQ and engine speed N in the form of a map shown in FIG. 5(A) in advance in the ROM 42.

[0041] Further, lubrication oil also includes sulfur in a certain ratio. The amount of lubrication oil which is burned in the combustion chamber 2, that is, the amount of SO.sub.X contained in the exhaust gas and trapped in the SO.sub.X trap catalyst 13, becomes a function of the required torque and engine speed. In this embodiment according to the present invention, the SO.sub.X amount SOXB contained in the lubrication oil and trapped per unit time in the SO.sub.X trap catalyst 13 is stored as a function of the required torque TQ and engine speed N in the form of a map such as shown in FIG. 5(B) in advance in the ROM 42. The sum of the SO.sub.X amount SOXA and SO.sub.X amount SOXB is cumulatively added to calculate the SO.sub.X amount .SIGMA.SOX trapped by the SO.sub.X trap catalyst 13.

[0042] Further, in this embodiment according to the present invention, as shown in FIG. 6, the relationship between the SO.sub.X amount .SIGMA.SOX and the predetermined SO.sub.X amount SO(n) when the SO.sub.X trap catalyst 13 should be regenerated is stored in advance. When the SO.sub.X amount .SIGMA.SOX has exceeded the predetermined SO(n) (n=1, 2, 3, . . . ), the regeneration treatment of the SO.sub.X trap catalyst 13 is performed. Note that in FIG. 6, n shows the number of times of the regeneration treatment. Note that, in FIG. 6, the initial regeneration treatment is performed when the driving distance is 50,000 km or so.

[0043] FIG. 7 shows a routine for determining the timing of regeneration of the SO.sub.X trap catalyst 13.

[0044] Referring to FIG. 7, first, at step 70, the SO.sub.X amounts SOXA and SOXB trapped per unit time are read from FIGS. 5(A),(B). Next at step 71, the sum of these SOXA and SOXB is added to the SO.sub.X amount .SIGMA.SOX. Next at step 72, SO.sub.X it is judged if the amount .SIGMA.SOX has reached the predetermined amount SO(n) (n=1, 2, 3, . . . ) shown in FIG. 6. When the SO.sub.X amount .SIGMA.SOX has reached the predetermined amount SO(n), the routine proceeds to step 73 where control is performed for regeneration.

[0045] Next, control for regeneration of the SO.sub.X trap catalyst 13 performed at step 73 of FIG. 7 will be explained.

[0046] FIG. 8 shows the relation between the SO.sub.X amount .SIGMA.SOX trapped at the SO.sub.X trap catalyst 13, the SO.sub.X release temperature TS from the SO.sub.X trap catalyst 13, and the air-fuel ratio A/F of the exhaust gas flowing into the SO.sub.X trap catalyst 13. From FIG. 8, it will be understood that the larger the trapped SO.sub.X amount .SIGMA.SOX, the lower the SO.sub.X release temperature TS, while the smaller the exhaust gas air-fuel ratio, the lower the SO.sub.X release temperature TS.

[0047] Now, in FIG. 8, if the temperature of the SO.sub.X trap catalyst 13 becomes excessively higher than the SO.sub.X release temperature TS determined from the trapped SO.sub.X amount .SIGMA.SOX, a large amount of SO.sub.X is rapidly released from the SO.sub.X trap catalyst 13. As a result, the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst 13 becomes extremely high. However as mentioned previously SO.sub.X itself is harmful. Further, if the temperature becomes higher, it sometimes changes to harmful hydrogen sulfide H.sub.2S, so it is necessary to avoid the SO.sub.X concentration in the exhaust gas, exhausted into the outside air, from becoming higher. That is, it is necessary to hold the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst 13 within a certain limit.

[0048] In this regard, if the engine load becomes larger or smaller, the exhaust gas temperature greatly fluctuates along with this. Therefore, during operation of the vehicle, it is difficult to prevent the temperature of the SO.sub.X trap catalyst 13 from becoming excessively higher than the SO.sub.X release temperature TS determined from the trapped SO.sub.X amount .SIGMA.NOX. Therefore, it is difficult to prevent the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst 13 from becoming higher by a large extent.

[0049] Therefore, in the present invention, when the power of the electric power device is borrowed to regenerate the SO.sub.X trap catalyst 13, the vehicle drive power from the engine and the vehicle drive power from the electric power device are adjusted so that the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst 13 becomes less than the predetermined SO.sub.X concentration during the regeneration period.

[0050] Explaining this a bit more specifically, when the SO.sub.X trap catalyst 13 should be regenerated, the output torque of the engine is controlled so that the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst 13 becomes less than the predetermined SO.sub.X concentration during the regeneration period and the shortage or excess of the torque with respect to the required torque is adjusted by the electric power device.

[0051] However, as explained previously, the SO.sub.X trap catalyst 13 can be regenerated in either the state where the exhaust gas air-fuel ratio A/F is made rich or the state where it is made lean. Therefore, first, the case of regenerating the SO.sub.X trap catalyst 13 in the state with the exhaust gas air-fuel ratio A/F made rich will be explained.

[0052] In this case, at the time of regeneration, the temperature of the SO.sub.X trap catalyst 13 is maintained at substantially the SO.sub.X release temperature TS. When the regeneration treatment progresses, the SO.sub.X release action causes the trapped SO.sub.X amount .SIGMA.SOX to decrease, so as will be understood from FIG. 8, the SO.sub.X release temperature TS rises. Therefore, in the present invention, to raise the exhaust gas temperature as the trapped SO.sub.X amount .SIGMA.SOX is decreased, as shown in FIG. 9, the output torque of the engine is increased, as the regeneration treatment progresses. Due to this, as shown in FIG. 9, the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst 13 is maintained at a predetermined concentration SX or less during the regeneration period. Note that in the example shown in FIG. 9, when the SO.sub.X amount .SIGMA.SOX has fallen to the predetermined amount SOR, the regeneration treatment is ended.

[0053] On the other hand, during the regeneration period, the shortage or excess of the torque with respect to the required torque is adjusted by the generation or consumption of the torque by the electric motor 27. To explain this, the relationship among the equivalent depression lines d.sub.1 to di of the accelerator pedal 32, the engine speed N, and the output torque of the engine TQ is shown in FIG. 10. Note that in FIG. 10, the amount of depression of the accelerator pedal 32 becomes greater from d.sub.1 to di. In FIG. 10, if the amount of depression of the accelerator pedal 32 and the engine speed N are determined, the output torque TQ at that time becomes the required torque.

[0054] That is, to maintain the temperature of the SO.sub.X trap catalyst 13 at the time of regeneration at substantially the SO.sub.X release temperature TS, assuming that the engine is made to operate in the operating state shown by the point A of FIG. 10. At this time, if the required torque TQ for driving the vehicle becomes the torque shown by the point B of FIG. 10, the electric motor 27 is driven to make up for the shortage .DELTA.TQb of the torque. As opposed to this, if the required torque TQ for driving the vehicle becomes the torque shown by the point C of FIG. 10, the electric motor 27 is made to operate as a generator to consume the excess .DELTA.TQc of the torque.

[0055] FIG. 11 shows the control for regeneration of the SO.sub.X trap catalyst 13 executed at step 73 of FIG. 7.

[0056] Referring to FIG. 11, first, at step 80, the required torque TQ for driving the vehicle is calculated based on the amount of depression of the accelerator pedal 32 and the engine speed N from FIG. 10. Next at step 81, the output torque of the engine Te required for making the temperature of the SO.sub.X trap catalyst 13 substantially the SO.sub.X release temperature TS is calculated. This output torque of the engine Te is stored as a function of the SO.sub.X amount .SIGMA.SOX, exhaust gas air-fuel ratio A/F, and engine speed N in advance in the ROM 42.

[0057] Next, at step 82, the output torque of the engine Te is subtracted from the required torque TQ to calculate the torque Tm which the electric motor 27 should generate or consume. Next at step 83, the fuel injection is controlled so that the output torque Te is obtained. Next at step 84, the electric motor 27 is controlled in accordance with the torque Tm. That is, when the torque Tm is positive, the electric motor 27 is driven so that the torque Tm for driving the vehicle is generated, while when the torque Tm is negative, the electric motor 27 is made to operate as a generator so as to consume the torque Tm.

[0058] Next, at step 85, it is judged if the regeneration treatment has ended. When the regeneration treatment has not ended, the routine returns to step 80. As opposed to this, when the regeneration treatment has ended, the routine proceeds to step 86 where the residual SO.sub.X amount SOR at the time of the end of regeneration is made the SO.sub.X amount .SIGMA.SOX.

[0059] FIG. 12 shows another embodiment of control for regeneration of the SO.sub.X trap catalyst 13 executed at step 73 of FIG. 7.

[0060] In this embodiment as well, basically, the output torque of the engine Te is made the output torque stored as a function of the SO.sub.X amount .SIGMA.SOX, exhaust gas air-fuel ratio A/F, and engine speed N in advance in the ROM 42, but in this embodiment, the output torque of the engine is corrected so that the SO.sub.X concentration detected by the SO.sub.X sensor 16 becomes a predetermined SO.sub.X concentration range.

[0061] That is, referring to FIG. 12, in this embodiment, first, at step 90, the required torque TQ for driving the vehicle is calculated based on the amount of depression of the accelerator pedal 32 and the engine speed N from FIG. 10. Next, at step 91, the output torque of the engine Te required for making the temperature of the SO.sub.X trap catalyst 13 substantially the SO.sub.X release temperature TS is calculated. Next at step 92, a correction amount .DELTA.TQ is added to the output torque Te to calculate the final output torque of the engine Teo (=Te+.DELTA.TQ).

[0062] Next at step 93, the final output torque of the engine Teo is subtracted from the required torque TQ to calculate the torque Tm which the electric motor 27 generates or consumes. Next at step 94, the fuel injection is controlled so that the final output torque of the engine Teo is obtained. Next at step 95, the electric motor 27 is controlled in accordance with the torque Tm. That is, as mentioned previously, when the torque Tm is positive, the electric motor 27 is driven so that the torque Tm for driving the vehicle is generated, while when the torque Tm is negative, the electric motor 27 is made to operate as a generator so as to consume the torque Tm.

[0063] Next, at step 96, it is judged if the regeneration treatment has ended. When the regeneration treatment has not ended, the routine proceeds to step 97 where to the SO.sub.X concentration SD in the exhaust gas flowing out from the SO.sub.X trap catalyst 13 is detected by the SO.sub.X sensor 16. Next at step 98, it is judged if the SO.sub.X concentration SD is larger than the sum of the reference SO.sub.X concentration SDo and a constant value .alpha.. When SD>SDo+.alpha., the routine proceeds to step 99 where the constant value m is subtracted from the correction amount .DELTA.TQ. As opposed to this, when SD.ltoreq.SDo+.alpha., the routine proceeds to step 100. When it is judged at step 100 that SD<SDo-.alpha., the routine proceeds to step 101 where the constant value m is added to the correction amount .DELTA.TQ. That is, the final output torque of the engine Teo is controlled so that the SO.sub.X concentration SD becomes the SDo-.alpha.<SD<SDo+.alpha.. On the other hand, when it is judged at step 96 that the regeneration treatment has ended, the routine proceeds to step 102 where the residual SO.sub.X amount SOR at the time of completion of regeneration is made the SO.sub.X amount .SIGMA.SOX.

[0064] Next, the case of trying to regenerate the SO.sub.X trap catalyst 13 in the state of making the exhaust gas air-fuel ratio A/F lean will be explained. In this case, as explained later, the temperature of the SO.sub.X trap catalyst 13 is raised to 600.degree. C. or so and is maintained at 600.degree. C. or so. However, in this case, as will be understood from the curve of A/F=16 of FIG. 8, when the SO.sub.X amount .SIGMA.SOX is large, the SO.sub.X release temperature TS becomes lower. Therefore, at this time, if raising the temperature of the SO.sub.X trap catalyst 13 to 600.degree. C. or so, a large amount of SO.sub.X ends up being released. That is, at this time, the temperature of the SO.sub.X trap catalyst 13 has to be maintained at substantially the SO.sub.X release temperature TS.

[0065] Therefore, when trying to regenerate the SO.sub.X trap catalyst 13 in the state where the air-fuel ratio A/F of the exhaust gas is made lean, as shown in FIG. 13, at the initial stage of the regeneration treatment, the output torque of the engine is gradually raised, then the output torque of the engine is held substantially constant. That is, in this case, the output torque of the engine is held substantially constant except at the initial stage of the regeneration treatment.

[0066] Next, another embodiment of an electric device will be explained with reference to FIG. 14.

[0067] Referring to FIG. 14, in this embodiment, the electric power device comprises a pair of motor-generators 200, 201 operating as an electric motor and generator and a planetary gear mechanism 202. This planetary gear mechanism 202 is provided with a sun gear 203, ring gear 204, planetary gear 205 arranged between the sun gear 203 and ring gear 204, and planetary carrier 206 carrying the planetary gear 205. The sun gear 203 is coupled with a shaft 207 of the motor-generator 201, while the planetary carrier 206 is coupled with an output shaft 211 of the internal combustion engine 1. Further, the ring gear 204 is on the one hand coupled with a shaft 208 of the motor-generator 200, while on the other hand is coupled with an output shaft 210 coupled to the drive wheels through a belt 209. Therefore, it is learned that when the ring gear 204 turns, the output shaft 210 is made to turn along with that.

[0068] An explanation of the detailed operation of this electric power device will be omitted, but generally speaking, the motor-generator 200 mainly operates as an electric motor, while the motor-generator 201 mainly operates as a generator.

[0069] When the torque is insufficient with just the output torque of the engine at the time of regeneration of the SO.sub.X trap catalyst 13, the motor-generator 200 is driven and the output torque of the motor-generator 200 is overlaid on the output torque of the engine. At this time, the motor-generator 201 is stopped. As opposed to this, at the time of regeneration of the SO.sub.X trap catalyst 13, when the output torque of the engine is in excess compared with the required torque, the power generation action of the motor-generator 201 is performed and the excess of the torque is consumed by the power generation action of the motor-generator 201. At this time, the motor-generator 200 is stopped.

Claims

1. An exhaust purification device of compression ignition type internal combustion engine arranging, in an engine exhaust passage, an SO.sub.X trap catalyst able to trap SO.sub.X contained in exhaust gas and arranging, in the exhaust passage downstream of the SO.sub.X trap catalyst, an NO.sub.X storage catalyst storing NO.sub.X contained in the exhaust gas when the air-fuel ratio of an inflowing exhaust gas is lean and releasing stored NO.sub.X when the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich, wherein said device is provided with an electric power device able to generate vehicle drive power separate from the vehicle drive power from the engine and able to generate electric power from the engine and, when the SO.sub.X trap catalyst should be regenerated, the vehicle drive power from the engine and the vehicle drive power from the electric power device are adjusted so that an SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst becomes less than a predetermined SO.sub.X concentration during a regeneration period.

2. An exhaust purification device of a compression ignition type internal combustion engine as set forth in claim 1, wherein when the SO.sub.X trap catalyst should be regenerated, the output torque of the engine is controlled so that the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst becomes less than the predetermined SO.sub.X concentration during the regeneration period, and a shortage or excess of the torque with respect to the required torque is adjusted by the electric power device.

3. An exhaust purification device of a compression ignition type internal combustion engine as set forth in claim 2, wherein the SO.sub.X trap catalyst is regenerated under a rich air-fuel ratio of exhaust gas flowing into the SO.sub.X trap catalyst and, at this time, the output torque of the engine is made to increase along with progress in a regeneration treatment.

4. An exhaust purification device of a compression ignition type internal combustion engine as set forth in claim 2, wherein the SO.sub.X trap catalyst is regenerated under a lean air-fuel ratio of exhaust gas flowing into the SO.sub.X trap catalyst and, at this time, the output torque of the engine is held substantially constant except at an initial stage of a regeneration treatment.

5. An exhaust purification device of a compression ignition type internal combustion engine as set forth in claim 2, wherein the SO.sub.X concentration in the exhaust gas flowing out from the SO.sub.X trap catalyst is detected, and the output torque of the engine is controlled so that a detected SO.sub.X concentration becomes within a predetermined SO.sub.X concentration range.