JP3807399B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

A technique has been proposed in which an NOx storage reduction catalyst (hereinafter referred to as NOx catalyst) is disposed in an exhaust passage of an internal combustion engine, and NOx in the exhaust is stored in the NOx catalyst.
By the way, in the NOx catalyst, sulfur oxide (SOx) generated by combustion of sulfur contained in the fuel is also stored by the same mechanism as NOx. The SOx stored in this way is less likely to be released than NOx and accumulates in the NOx catalyst. This is called sulfur poisoning (SOx poisoning), and the NOx purification rate decreases. Therefore, it is necessary to perform poisoning recovery processing for recovering from sulfur poisoning at an appropriate time. This poisoning recovery process is performed by circulating exhaust gas having a reduced oxygen concentration while keeping the NOx catalyst at a high temperature (for example, about 600 to 650 ° C.) (see, for example, Patent Document 1).

Further, in a hybrid vehicle, a technique is known in which when the temperature of a catalyst is in an inactive state, motor driving is prohibited and an internal combustion engine is idle (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 7-217474 Japanese Patent Laid-Open No. 10-288063 JP 2001-241341 A JP 2000-186536 A

  By the way, when the internal combustion engine is operated at a low output, exhaust gas having a low temperature is discharged from the internal combustion engine. When the sulfur poisoning recovery process is performed and the temperature of the catalyst is increased, if the internal combustion engine is operated at a low output, exhaust gas having a low temperature flows into the catalyst and the temperature of the catalyst decreases. End up. As a result, the temperature of the catalyst must be increased again, and it may take time to complete the sulfur poisoning recovery.

  The present invention has been made to solve the above problems, and in an exhaust gas purification apparatus for an internal combustion engine in a hybrid vehicle, the temperature of the catalyst is lowered by operating the internal combustion engine in a low output state. An object of the present invention is to provide a technique capable of suppressing the above.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is,
In an exhaust gas purification apparatus for an internal combustion engine in a hybrid vehicle that includes a catalyst in an exhaust passage of the internal combustion engine and is capable of running using the electric motor as a power source with the internal combustion engine stopped
Further comprising catalyst temperature raising means for raising the temperature of the catalyst,
When a request to increase the temperature of the catalyst is made ,
When the operating state of the internal combustion engine is not in a state of lowering the temperature of the catalyst, the operation of the internal combustion engine is continued,
The operation of the internal combustion engine is stopped when the temperature of the catalyst is lowered, and the operation of the internal combustion engine is stopped, and when the vehicle is driven, the electric motor is used as a power source. To do.

  The greatest feature of the present invention is that when the temperature of the exhaust gas is low and the temperature of the catalyst may be lowered, the internal combustion engine is stopped to prevent the low temperature exhaust gas from flowing into the catalyst. It is in suppressing the fall of the.

  That is, when it is necessary to increase the temperature of the catalyst or to maintain the temperature thereafter, if the exhaust gas having a low temperature at the time of low output flows into the catalyst, the temperature of the catalyst will decrease. In that respect, the hybrid vehicle can travel by the electric motor even when the internal combustion engine is stopped. Therefore, when there is a possibility that low-temperature exhaust gas may flow into the catalyst, it is possible to suppress a decrease in the temperature of the catalyst by stopping the internal combustion engine and further running the vehicle with an electric motor. Become.

In the present invention, the hybrid vehicle travels by an electric motor at least in a low output region of the vehicle, and when the temperature of the catalyst is increased by the catalyst temperature increasing means, compared to when the temperature is not increased, A region where the vehicle is driven by the electric motor can be expanded to a higher output side while leaving a region where the vehicle is driven by the internal combustion engine .

  The hybrid vehicle travels by switching between the electric motor and the internal combustion engine according to the output state of the vehicle. For example, when the output of the internal combustion engine becomes 5 kW or less, the internal combustion engine is stopped and switched to the electric motor. The output condition of the vehicle to be switched is determined based on fuel consumption, drivability, and the like. In the present invention, when the temperature of the catalyst is increased, the output condition of the vehicle that switches between the internal combustion engine and the electric motor is set to a higher output side. By doing in this way, an internal combustion engine will be stopped in the state where exhaust temperature is higher, and it can control that the temperature of a catalyst falls. The output condition of the vehicle that switches between the internal combustion engine and the electric motor may be the output condition of the vehicle that stops the internal combustion engine. Further, the output of the vehicle may be an output required for the vehicle.

  In the present invention, the catalyst is a NOx storage reduction catalyst, and when the temperature of the catalyst is raised, even when the sulfur poisoning of the NOx storage reduction catalyst is recovered. good.

  The catalyst is a catalyst supported on the particulate filter or a catalyst provided upstream of the particulate filter. When the temperature of the catalyst is rising, the catalyst is collected by the particulate filter. It may be when the particulate matter is oxidized.

  When recovering sulfur poisoning of the NOx storage reduction catalyst or oxidizing and removing particulate matter collected by the particulate filter, the temperature of the catalyst is raised. If the temperature of the catalyst decreases at this time, the temperature of the catalyst must be increased again, and it takes time to complete the recovery from sulfur poisoning and the removal of particulate matter. Further, extra energy is required to raise the temperature of the catalyst, which may cause a deterioration in fuel consumption. In that respect, according to the present invention, it is possible to suppress the temperature of the catalyst from decreasing during the sulfur poisoning recovery process or during the oxidation of the particulate matter, and to quickly complete the recovery of the sulfur poisoning or It is possible to complete the removal.

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the temperature of the catalyst needs to be raised, the temperature of the catalyst can be prevented from lowering.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of a hybrid system according to the present embodiment and an exhaust system of an internal combustion engine.
The hybrid vehicle according to the present embodiment includes an internal combustion engine 1, a power split mechanism 31, an electric motor 32, a generator 33, a battery 34, an inverter 35, an axle 36, a speed reducer 37, and wheels 38.

  The power split mechanism 31 distributes the output from the internal combustion engine 1 to the generator 33 and the axle 36. The power split mechanism 31 also has a function of transmitting the output from the electric motor 32 to the axle 36. The electric motor 32 rotates at a rotational speed proportional to the axle 36 via the speed reducer 37. The electric motor 32 can assist the output of the internal combustion engine 1 as necessary during normal operation. A battery 34 is connected to the electric motor 32 and the generator 33 via an inverter 35. The generator 33 obtains power from the internal combustion engine 1 to generate power and charge the battery 34.

  In the hybrid system configured as described above, during normal traveling, the wheel 36 is driven by rotating the axle 36 by the output of the internal combustion engine 1 or the output of the electric motor 32. Further, the wheel 36 can be driven by rotating the axle 36 by combining the output of the internal combustion engine 1 and the output of the electric motor 32. On the other hand, at the time of deceleration, the kinetic energy can be converted into electric energy and recovered by the battery 34 by operating the electric motor 32 with the generator 33 as the generator by the rotational force of the wheel 38. Thus, since the kinetic energy is converted into electric energy when the vehicle is decelerated, it is possible to assist the deceleration of the vehicle.

Next, the internal combustion engine 1 is an in-cylinder direct injection gasoline engine that directly injects fuel into a cylinder. The internal combustion engine 1 is an engine that can be operated by lean combustion.
The internal combustion engine 1 is provided with a fuel injection valve 5 that injects fuel into the cylinder. Further, an exhaust passage 2 leading to the combustion chamber is connected to the internal combustion engine 1. This exhaust passage 2 communicates with the atmosphere downstream.

An occlusion reduction type NOx catalyst 4 (hereinafter referred to as NOx catalyst 4) is provided in the exhaust passage 2.
The NOx catalyst 4 has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. Have.

  The NOx catalyst 4 also stores sulfur components contained in the fuel. This is called sulfur poisoning (SOx poisoning). Due to this sulfur poisoning, the amount of NOx that can be stored decreases, and the purification rate of NOx decreases. Therefore, it is necessary to perform poisoning recovery processing for recovering the NOx catalyst 4 from sulfur poisoning. This poisoning recovery process is performed by causing the NOx catalyst 4 to flow through the NOx catalyst 4 while reducing the oxygen concentration while keeping the NOx catalyst 4 in a high temperature state (for example, about 600 to 650 ° C.).

  For example, the temperature of the exhaust gas can be raised by delaying the timing for injecting fuel from the fuel injection valve 5, thereby raising the temperature of the NOx catalyst 4. Further, by operating the internal combustion engine 1 with a rich air-fuel ratio, it is possible to circulate exhaust with reduced oxygen concentration through the NOx catalyst 4.

In addition, as a method for increasing the temperature of the NOx catalyst 4 or decreasing the oxygen concentration of the exhaust gas, low-temperature combustion in which the amount of recirculated EGR gas is increased more than the maximum amount of soot generation, fuel injection into the cylinder There are methods such as changing the timing and the number of times, adding fuel to the exhaust, and operating the internal combustion engine 1 with a rich air-fuel ratio, and supplying secondary air to the NOx catalyst 4. That is, these can be used as the catalyst temperature raising means in the present invention.

  The internal combustion engine 1 configured as described above is provided with an ECU 6 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 6 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  The ECU 6 outputs an electric signal corresponding to the amount of depression of the accelerator by the driver, and an accelerator opening sensor 7 that can detect the load state of the vehicle, and a crank position sensor 8 that detects the rotational speed of the internal combustion engine 1. In addition, various sensors are connected via electric wiring, and output signals of the various sensors described above are input to the ECU 6.

On the other hand, the fuel injection valve 5 and the like are connected to the ECU 6 via electric wiring, and can be controlled by the ECU 6.
Further, the ECU 6 stores various application programs and various control maps.

  Here, as described above, when the sulfur poisoning of the NOx catalyst 4 is recovered, it is necessary to keep the temperature of the NOx catalyst 4 high. However, when the output of the internal combustion engine 1 decreases due to a decrease in the output required for the vehicle at the time of sulfur poisoning recovery, the temperature of the exhaust gas discharged from the internal combustion engine decreases. Further, when the exhaust gas passes through the NOx catalyst 4, the temperature of the NOx catalyst 4 is lowered. In that respect, when the internal combustion engine 1 is stopped and the vehicle is driven by the electric motor 32, the exhaust gas does not flow through the exhaust passage 2, so that the temperature of the NOx catalyst 4 is not lowered by the exhaust gas.

  Therefore, in this embodiment, at the time of recovery from sulfur poisoning, the internal combustion engine 1 is stopped in a state where the output of the internal combustion engine 1 is higher so that a decrease in the temperature of the NOx catalyst 4 necessary for the recovery from sulfur poisoning can be suppressed. The vehicle is driven by the electric motor 32.

  FIG. 2 is a diagram showing the relationship between the rotational speed of the internal combustion engine, the generated torque (load), and the stop region of the internal combustion engine when the sulfur poisoning recovery control is not performed. The lower the torque generated by the internal combustion engine 1, the lower the load on the internal combustion engine. Further, the lower the rotation speed or load of the internal combustion engine, that is, the closer to the lower left corner of FIG. On the other hand, the higher the engine speed or load, that is, the closer to the upper right in FIG. 2, the greater the output required for the vehicle.

  Here, when the rotation speed or load of the internal combustion engine 1 shifts from the high rotation high load side to the lower side of the line indicated by the engine OFF, that is, when the rotation speed is low or the load is low, the internal combustion engine 1 is stopped. Is done. Note that, since the internal combustion engine 1 is stopped below the line indicated by the engine OFF, the rotational speed and the generated torque (load) are actually 0, but in FIG. 2, the engine OFF is indicated. Even if the operating state of the internal combustion engine 1 shifts below the line, the generated torque and the rotational speed when the internal combustion engine 1 is not stopped are shown. The generated torque of the internal combustion engine may be a vehicle load.

On the other hand, even when the output required for the vehicle shifts from the low rotation / low load side to the high rotation / high load side than the line indicated by the engine OFF, the internal combustion engine 1 is not started and the engine speed or load is further increased. The internal combustion engine 1 is started when it rises and rises to the line indicated by the engine ON. As described above, the start and stop of the internal combustion engine 1 are performed in different operating states because of demands from drivability and the like.

  Further, in the region on the higher rotation or higher load side than the sulfur poisoning recoverable boundary line, the temperature of the exhaust gas flowing into the NOx catalyst 4 is high, and the temperature of the NOx catalyst 4 is increased to a temperature necessary for sulfur poisoning recovery. It is a possible operating range (hereinafter referred to as a sulfur poisoning recoverable range). Here, the sulfur poisoning recoverable boundary line means an iso-output line or an exhaust temperature distribution.

  And in FIG. 2, the line shown by engine OFF is set to the low rotation low load side rather than the sulfur poisoning recovery possible boundary line. In such a setting, when the sulfur poisoning recovery control is being performed, the internal combustion engine 1 is stopped when the operating state of the internal combustion engine 1 shifts to a lower rotation and lower load side than the sulfur poisoning recovery possible region. In the operating region between the sulfur poisoning recoverable boundary line and the line indicated by the engine OFF, the low-temperature exhaust gas passes through the NOx catalyst 4 and the temperature of the NOx catalyst 4 decreases. End up.

  In this respect, in this embodiment, at the time of sulfur poisoning recovery, the line indicated by the engine OFF is in the sulfur poisoning recoverable region, that is, the line indicated by the engine OFF is the sulfur poisoning recoverable boundary line. The stop condition (line indicated by the engine OFF) of the internal combustion engine 1 is set so as to be on the higher rotation and higher load side (high output side).

  Here, FIG. 3 is a diagram showing the relationship among the rotational speed of the internal combustion engine, the generated torque (load), and the stop region of the internal combustion engine when performing the sulfur poisoning recovery control. In this way, the operation state of the internal combustion engine 1 shifts to the low rotation low load side (low output side) during the sulfur poisoning recovery control, and as a result, low temperature exhaust gas passes through the NOx catalyst 4. It becomes possible to stop the internal combustion engine 1 before it becomes.

Next, control for changing the operating condition for stopping the internal combustion engine 1 at the time of sulfur poisoning recovery according to this embodiment will be described.
FIG. 4 is a flowchart showing a flow of the internal combustion engine stop condition change control according to this embodiment.

In step S101, it is determined whether the sulfur poisoning recovery condition of the NOx catalyst 4 is satisfied.
Examples of conditions include whether the amount of SOx stored in the NOx catalyst 4 exceeds a specified amount. Here, the SOx storage amount can be obtained from the fuel consumption, the output signal from the NOx sensor, the travel distance of the vehicle, and the like. That is, since the NOx catalyst 4 is poisoned by the sulfur component in the fuel, the fuel consumption may be integrated and stored in the ECU 6, and the SOx storage amount may be obtained from this fuel consumption. Further, when sulfur poisoning of the NOx catalyst 4 progresses, the NOx occlusion capacity of the NOx catalyst 4 decreases, so that the amount of NOx that is not stored in the NOx catalyst 4 and slips downstream of the NOx catalyst 4 increases. Therefore, a NOx sensor may be provided downstream of the NOx catalyst 4, and the SOx storage amount may be obtained based on this output signal. Further, assuming that the SOx storage amount increases according to the vehicle travel distance, the SOx storage amount may be obtained based on the vehicle travel distance.

If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, the sulfur poisoning recovery process is not performed, and thus this routine is terminated.
In step S102, the stop condition of the internal combustion engine 1, that is, the switching condition for driving the vehicle by the electric motor 32 is shifted to a higher load or higher rotation side, that is, higher output side.

The switching condition here refers to the line indicated by the engine OFF, but the line indicated by the engine ON may also be shifted to the high output side.
In this way, a decrease in the temperature of the NOx catalyst 4 that occurs when the internal combustion engine 1 is operated in a low output state can be suppressed. Further, when the internal combustion engine 1 is started next time, the temperature of the NOx catalyst 4 can be quickly raised to a temperature required for the sulfur poisoning recovery process. As a result, it is possible to shorten the time required to complete the recovery from sulfur poisoning, and to improve fuel efficiency.

  The NOx catalyst 4 may be another catalyst having an oxidation function, such as an oxidation catalyst or a three-way catalyst.

  In the first embodiment, the suppression of the temperature drop of the NOx catalyst 4 during the sulfur poisoning recovery process of the NOx catalyst 4 has been described. However, in this embodiment, a particulate filter is provided and collected in the filter. An example applied to the case where the temperature of the filter is raised to oxidize and remove the particulate matter formed will be described. Since other configurations are the same as those of the first embodiment, description thereof is omitted. Here, it is assumed that the NOx catalyst 4 is carried on the particulate filter 40.

  By providing the particulate filter 40 (hereinafter referred to as the filter 40) in the exhaust passage of the internal combustion engine 1, particulate matter (hereinafter referred to as PM) in the exhaust can be collected by the filter 40. And the technique of oxidizing and removing PM collected by the filter 40 by supplying fuel to the filter 40 and raising the temperature of the filter 40 is known. The removal of the PM collected by the filter 40 in this way is called regeneration of the filter 40.

  Here, the temperature of the filter 40 can be raised by adding fuel in the exhaust gas in the same manner as in the sulfur poisoning recovery described in the first embodiment. At that time, when the operating state of the internal combustion engine 1 shifts to the low rotation / low load (low output) operating region, the low temperature exhaust gas flows into the filter 40, and the temperature of the filter 40 is lowered.

In this regard, in the present embodiment, the internal combustion engine 1 is stopped before the temperature of the filter 40 decreases, and the vehicle is driven by switching the power source of the vehicle to the electric motor 32.
In this case, instead of the sulfur poisoning recoverable region described in the first embodiment, a filter regeneration possible region is set. The filter reproducible region here refers to an operation region in which the temperature of the exhaust gas flowing into the filter 40 is high and the temperature of the filter 40 can be set to a temperature at which the filter can be regenerated. . And it sets so that the line shown by the engine OFF may be located in this filter regeneration possible field.

  In this way, even when the operating state of the internal combustion engine 1 shifts to the low rotation / low load (low output) region during the regeneration of the filter 40, the temperature of the filter 40 is reduced by stopping the internal combustion engine 1. Can be suppressed. Thereby, the time required for regeneration of the filter 40 can be shortened, and deterioration of fuel consumption can be suppressed.

  In the present embodiment, the NOx catalyst 4 is carried on the filter 40. Alternatively, the NOx catalyst 4 may be provided upstream of the filter 40. The NOx catalyst 4 may be another catalyst having an oxidation function, such as an oxidation catalyst or a three-way catalyst.

It is a figure which shows schematic structure of the hybrid system by an Example, and the exhaust system of an internal combustion engine. It is the figure which showed the relationship between the rotation speed of an internal combustion engine, generated torque (load), and the stop area | region of an internal combustion engine when not performing sulfur poisoning recovery control. It is the figure which showed the relationship between the rotation speed of an internal combustion engine, generated torque (load), and the stop area | region of an internal combustion engine when performing sulfur poisoning recovery control. It is the flowchart figure which showed the flow of the internal combustion engine stop condition change control by an Example.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passage 4 NOx storage reduction catalyst 5 Fuel addition valve 6 ECU
7 Accelerator opening sensor 8 Crank position sensor 31 Power split mechanism 32 Electric motor 33 Generator 34 Battery 35 Inverter 36 Axle 37 Reducer 38 Wheel 40 Particulate filter

Claims (4)

In an exhaust gas purification apparatus for an internal combustion engine in a hybrid vehicle that includes a catalyst in an exhaust passage of the internal combustion engine and is capable of running using the electric motor as a power source with the internal combustion engine stopped
Further comprising catalyst temperature raising means for raising the temperature of the catalyst,
When a request to increase the temperature of the catalyst is made ,
When the operating state of the internal combustion engine is not in a state of lowering the temperature of the catalyst, the operation of the internal combustion engine is continued,
The operation of the internal combustion engine is stopped when the temperature of the catalyst is lowered, and the operation of the internal combustion engine is stopped, and when the vehicle is driven, the electric motor is used as a power source. An exhaust purification device for an internal combustion engine.   The hybrid vehicle travels by an electric motor at least in a low output region of the vehicle, and when the temperature of the catalyst is increased by the catalyst temperature increasing means, the vehicle is driven by an internal combustion engine as compared to when the temperature is not increased. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein a region in which the vehicle is driven by the electric motor is expanded to a higher output side while leaving the region to be driven. The catalyst is an NOx storage reduction catalyst, and when the temperature of the catalyst is increased,
The sulfur reduction of the NOx storage reduction catalyst is being recovered.
Or an exhaust emission control device for an internal combustion engine according to 2 or 2, The catalyst is a catalyst supported on a particulate filter or a catalyst provided upstream of the particulate filter, and when the temperature of the catalyst is rising, particles collected on the particulate filter 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas is oxidized.

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