The present invention relates to an exhaust purification device of a compression ignition type internal combustion engine.
Known in the art is an internal combustion engine arranging in an engine exhaust passage an NOX storage catalyst storing NOX contained in exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releasing the stored NOX when the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich. In this internal combustion engine, NOX formed when burning fuel under a lean air-fuel ratio is stored in the NOX storage catalyst. On the other hand, as the NOX storage catalyst approaches saturation of the NOX storage ability, the air-fuel ratio of the exhaust gas is temporarily made rich, whereby NOX is released from the NOX storage catalyst and reduced.
However, fuel and lubrication oil contain sulfur. Therefore, the exhaust gas also contains SOX. This SOX is stored together with the NOX in the NOX storage catalyst. This SOX is not released from the NOX storage catalyst by just making the exhaust gas a rich air-fuel ratio. Therefore, the amount of SOX stored in the NOX storage catalyst gradually increases. As a result, the storable NOX amount ends up gradually decreasing.
However, in this case, if raising the temperature of the NOX storage catalyst and making the air-fuel ratio of the exhaust gas flowing into the NOX storage catalyst rich, the SOX stored in the NOX storage catalyst is gradually released from the NOX storage catalyst. Therefore, there is known a hybrid internal combustion engine provided with an electric motor, in which when SOX should be released from the NOX 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).
On the other hand, there is known an internal combustion engine in which an SOX trap catalyst able to trap the SOX in the exhaust gas is arranged in the engine exhaust passage upstream of the NOX storage catalyst (see Japanese Patent Publication (A) No. 2005-133610). In this internal combustion engine, by trapping the SOX contained in the exhaust gas by the SOX trap catalyst, the inflow of SOX into the NOX storage catalyst is prevented.
However, even when using such an SOX trap catalyst, when the SOX trap rate of the SOX trap catalyst falls, it is necessary to regenerate the SOX trap catalyst. In this case, the SOX trap catalyst can be regenerated by raising the temperature of the SOX trap catalyst. However, the amount of SOX trapped by this SOX trap catalyst is much greater than the amount of SOX stored in the NOX storage catalyst, and thus, if the SOX trap catalyst is excessively raised in temperature even a little, the trapped SOX is released all at once. As a result, the SOX concentration in the exhaust gas flowing out from the SOX trap catalyst ends up becoming extremely high.
SOX is itself harmful, and if the temperature becomes higher, SOX sometimes changes to harmful hydrogen sulfide H2S. Therefore, it is necessary to avoid the concentration of SOX in the exhaust gas, which is exhausted into the outside air, from becoming high. That is, when using an SOX trap catalyst, it is necessary to hold the concentration of SOX in the exhaust gas flowing out from the SOX trap catalyst within a constant limit.
An object of the present invention is to provide a compression ignition type internal combustion engine able to hold the SOX concentration in the exhaust gas flowing out from the SOX trap catalyst at a certain limit or lower.
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 SOX trap catalyst able to trap SOX contained in exhaust gas and arranging, in the exhaust passage downstream of the SOX trap catalyst, an NOX storage catalyst storing NOX contained in the exhaust gas when the air-fuel ratio of an inflowing exhaust gas is lean and releasing stored NOX 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 SOX 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 SOX concentration in the exhaust gas flowing out from the SOX trap catalyst becomes less than a predetermined SOX concentration during a regeneration period.
Referring to
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 SOX trap catalyst 13 and NOX storage catalyst 14 are arranged in this order from the upstream side. Inside the catalyst converter 12 between the SOX trap catalyst 13 and the NOX storage catalyst 14, a temperature sensor 15 for detecting the temperature of the exhaust gas flowing out from the SOX trap catalyst 13 and an SOX sensor 16 for detecting the SOX concentration in the exhaust gas flowing out from the SOX trap catalyst 13 are provided. In the embodiment according to the present invention, the temperature of the SOX trap catalyst 13 is estimated from the detection value of this temperature sensor 15.
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
On the other hand, in the embodiment shown in
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
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 SOX 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.
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°. 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.
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.
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.
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.
Next, the NOX storage catalyst 14 shown in
In the embodiment according to the present invention, as the precious metal catalyst 61, platinum Pt is used. As the ingredient forming the NOX 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.
If the ratio of the air and fuel (hydrocarbons) fed into the engine intake passage, combustion chamber 2, and exhaust passage upstream of the NOX storage catalyst 14 is called the “air-fuel ratio of the exhaust gas”, an NOX absorption and release action such that the NOX absorbent 62 absorbs the NOX when the air-fuel ratio of the exhaust gas is lean and releases the absorbed NOX when the oxygen concentration in the exhaust gas falls is performed.
That is, explaining this taking as an example the case of using barium Ba as the ingredient forming the NOX 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
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 (NO3−→NO2), therefore the nitrate ions NO3 in the NOX absorbent 62 are released in the form of NO2 from the NOX absorbent 62. Next, the released NOX is reduced by the unburned HC and CO contained in the exhaust gas.
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 NOX in the exhaust gas is absorbed in the NOX absorbent 62. However, when the fuel continues to be burned under a lean air-fuel ratio, the NOX absorbent 62 eventually ends up becoming saturated in NOX absorption ability, therefore the NOX absorbent 62 ends up becoming unable to absorb the NOX. Therefore, in this embodiment of the present invention, before the NOX 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 NOX absorbent 62 release the NOX.
On the other hand, the exhaust gas contains SOX, that is, SO2. If this SO2 flows into the NOX storage catalyst 14, this SO2 is oxidized on the platinum Pt 61 and becomes SO3. Next, this SO3 is absorbed in the NOX absorbent 62, bonds with the barium oxide BaO, is diffused in the form of sulfate ions SO42− in the NOX absorbent 62, and forms stable sulfate BaSO4. However, the NOX absorbent 62 has a strong basicity, so this sulfate BaSO4 is stable and hard to break down. If just making the exhaust gas rich air-fuel ratio, the sulfate BaSO4 remains as is without breaking down. Therefore, in the NOX absorbent 62, the sulfate BaSO4 increases along with the elapse of time, therefore the NOX amount which the NOX absorbent 62 can absorb falls along with the elapse of time.
In this regard, in this case, if making the air-fuel ratio of the exhaust gas flowing into the NOX storage catalyst 14 rich in the state where the temperature of the NOX storage catalyst 14 is made to rise to the SOX release temperature of 600° C. or more, the NOX absorbent 62 releases SOX. However, in this case, the NOX absorbent 62 only releases a little SOX at a time. Therefore, to make the NOX absorbent 62 release all of the absorbed SOX, 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.
Therefore, in an embodiment of the present invention, the SOX trap catalyst 13 is arranged upstream of the NOX storage catalyst 14 to trap the SOX contained in the exhaust gas by this SOX trap catalyst 13 and thereby prevent SOX from flowing into the NOX storage catalyst 14. Next this SOX trap catalyst 13 will be explained.
Now, the SOX contained in the exhaust gas, that is, SO2, is oxidized on the platinum Pt 67 as shown in
In
For example, if raising the temperature of the SOX trap catalyst 13 when the exhaust gas air-fuel ratio is lean, the SOX 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 SOX present near the surface of the coat layer 66 diffuses toward the deep part of the coat layer 66, the SOX concentration near the surface of the coat layer 66 falls. Therefore, when the temperature raising control of the SOX trap catalyst 13 has ended, the SOX trap rate is restored.
If making the temperature of the SOX trap catalyst 13 about 450° C. when performing the temperature raising control of the SOX trap catalyst 13, it is possible to make the SOX present near the surface of the coat layer 66 diffuse in the coat layer 66. If raising the temperature of the SOX trap catalyst 13 to 600° C. or so, the SOX 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 SOX trap catalyst 13, the temperature of the SOX trap catalyst 13 is raised to 600° C. or so and is held at 600° C. or so.
On the other hand, even if making the air-fuel ratio of the exhaust gas flowing into the SOX trap catalyst 13 rich in the state raising the temperature of the SOX trap catalyst 13, the SOX trap rate can be restored. That is, if making the air-fuel ratio of the exhaust gas flowing into the SOX trap catalyst 13 in the state of raising the temperature of the SOX trap catalyst 13 rich, the trapped SOX is released from the SOX trap catalyst 13 and therefore the SOX trap rate is restored. Therefore, both when making the air-fuel ratio of the exhaust gas flowing into the SOX trap catalyst 13 lean and rich in the state raising the temperature of the SOX trap catalyst 13, the SOX trap rate can be restored.
Next, the timing of start of the action for regeneration of the SOX trap catalyst 13 for restoring the SOX trap rate will be explained.
In this embodiment according to the present invention, the SOX amount trapped by the SOX trap catalyst 13 is estimated. When the SOX amount trapped by the SOX trap catalyst 13 exceeds a predetermined amount, it is judged that the SOX trap rate has fallen below the predetermined rate. At this time, the action for regeneration of the SOX trap catalyst 13 for restoration of the SOX trap rate is started.
That is, fuel contains sulfur in a certain ratio. Therefore, the amount of SOX contained in the exhaust gas, that is, the amount of SOX trapped by the SOX 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 SOX trapped by the SOX trap catalyst 13 becomes a function of the required torque and engine speed. In this embodiment according to the present invention, the SOX amount SOXA trapped per unit time in the SOX 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
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 SOX contained in the exhaust gas and trapped in the SOX trap catalyst 13, becomes a function of the required torque and engine speed. In this embodiment according to the present invention, the SOX amount SOXB contained in the lubrication oil and trapped per unit time in the SOX 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
Further, in this embodiment according to the present invention, as shown in
Referring to
Next, control for regeneration of the SOX trap catalyst 13 performed at step 73 of
Now, in
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 SOX trap catalyst 13 from becoming excessively higher than the SOX release temperature TS determined from the trapped SOX amount ΣNOX. Therefore, it is difficult to prevent the SOX concentration in the exhaust gas flowing out from the SOX trap catalyst 13 from becoming higher by a large extent.
Therefore, in the present invention, when the power of the electric power device is borrowed to regenerate the SOX 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 SOX concentration in the exhaust gas flowing out from the SOX trap catalyst 13 becomes less than the predetermined SOX concentration during the regeneration period.
Explaining this a bit more specifically, when the SOX trap catalyst 13 should be regenerated, the output torque of the engine is controlled so that the SOX concentration in the exhaust gas flowing out from the SOX trap catalyst 13 becomes less than the predetermined SOX 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.
However, as explained previously, the SOX 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 SOX trap catalyst 13 in the state with the exhaust gas air-fuel ratio A/F made rich will be explained.
In this case, at the time of regeneration, the temperature of the SOX trap catalyst 13 is maintained at substantially the SOX release temperature TS. When the regeneration treatment progresses, the SOX release action causes the trapped SOX amount ΣSOX to decrease, so as will be understood from
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 d1 to di of the accelerator pedal 32, the engine speed N, and the output torque of the engine TQ is shown in
That is, to maintain the temperature of the SOX trap catalyst 13 at the time of regeneration at substantially the SOX release temperature TS, assuming that the engine is made to operate in the operating state shown by the point A of
Referring to
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.
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 SOX amount SOR at the time of the end of regeneration is made the SOX amount ΣSOX.
In this embodiment as well, basically, the output torque of the engine Te is made the output torque stored as a function of the SOX amount ΣSOX, 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 SOX concentration detected by the SOX sensor 16 becomes a predetermined SOX concentration range.
That is, referring to
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.
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 SOX concentration SD in the exhaust gas flowing out from the SOX trap catalyst 13 is detected by the SOX sensor 16. Next at step 98, it is judged if the SOX concentration SD is larger than the sum of the reference SOX concentration SDo and a constant value α. When SD>SDo+α, the routine proceeds to step 99 where the constant value m is subtracted from the correction amount ΔTQ. As opposed to this, when SD≦SDo+α, the routine proceeds to step 100. When it is judged at step 100 that SD<SDo−α, the routine proceeds to step 101 where the constant value m is added to the correction amount ΔTQ. That is, the final output torque of the engine Teo is controlled so that the SOX concentration SD becomes the SDo−α<SD<SDo+α. 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 SOX amount SOR at the time of completion of regeneration is made the SOX amount ΣSOX.
Next, the case of trying to regenerate the SOX 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 SOX trap catalyst 13 is raised to 600° C. or so and is maintained at 600° C. or so. However, in this case, as will be understood from the curve of A/F=16 of
Therefore, when trying to regenerate the SOX trap catalyst 13 in the state where the air-fuel ratio A/F of the exhaust gas is made lean, as shown in
Next, another embodiment of an electric device will be explained with reference to
Referring to
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.
When the torque is insufficient with just the output torque of the engine at the time of regeneration of the SOX 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 SOX 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.
Number | Date | Country | Kind |
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2007-016432 | Jan 2007 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2008/051467 | 1/24/2008 | WO | 00 | 8/4/2008 |