JP5983012B2 - Exhaust gas purification method and apparatus for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification method and apparatus for an internal combustion engine.

  In an internal combustion engine, particularly an automobile diesel engine, an oxidation catalyst is disposed in an exhaust system to reduce HC and CO in exhaust gas. The oxidation catalyst generally contains a noble metal, and exhibits a sufficient purification ability at a high temperature above a predetermined temperature. On the other hand, in recent years, a high purification performance is required due to environmental problems, and a situation in which a decrease in the temperature of exhaust gas serving as a heat source is unavoidable due to the improvement in traveling fuel consumption. Patent Document 1 proposes to provide an electric heater in the oxidation catalyst in order to raise the oxidation catalyst to the activation temperature at an early stage.

Japanese Patent Laid-Open No. 11-294152

  As described in Patent Document 1, when the oxidation catalyst is heated by an electric heater to increase its temperature, an electric heater is separately required and the fuel consumption is deteriorated by the amount of heating.

  The present invention has been made in consideration of the above circumstances, and its purpose is to eliminate the need for a separate heating means, or to provide a sufficient shortening of the operation time even if a separate heating means is provided. An object of the present invention is to provide an exhaust gas purification method and apparatus for an internal combustion engine.

  In order to achieve the above object, in the present invention, the oxidation catalyst is basically based on the knowledge that if a sufficient amount of oxygen is adsorbed on the noble metal even at a low temperature, the oxidation ability can be exhibited. Is based.

Specifically, in the method of the present invention, the following solution is adopted. That is, as described in claim 1,
An exhaust gas purification method for an internal combustion engine having an oxidation catalyst in an exhaust system,
A first step of predicting the amount of oxygen adsorbed on the noble metal of the oxidation catalyst;
When the oxygen adsorption amount predicted in the first step is less than or equal to a predetermined lower limit set in advance, second control for scavenging the noble metal of the oxidation catalyst and increasing the oxygen adsorption amount on the noble metal is executed. Steps,
Bei to give a,
The increase control of the oxygen adsorption amount to the noble metal in the second step is performed by scavenging the noble metal of the oxidation catalyst with the high-temperature air discharged to the exhaust system without burning in the cylinder due to the fuel cut during traveling. Done,
It is like that. According to the above-described solution technique, the amount of oxygen adsorbed on the noble metal is sufficiently increased by executing the increase control of the amount of oxygen adsorbed on the noble metal by scavenging the noble metal of the oxidation catalyst, so that the low temperature state lower than the activation temperature. But it can oxidize the unburned gas in the exhaust gas. Thereby, it is not necessary to separately provide a heating means for heating the oxidation catalyst, or even if a heating means is provided, the operation time can be shortened. In addition to the above, intake air (oxygen in it) can be supplied to the oxidation catalyst by a simple method of fuel cut to scavenge noble metals. Further, it is not necessary to separately use a special device for scavenging.

A preferred mode based on the above solution is as described in claim 2 and the following claims. That is,
The prediction of the oxygen adsorption amount to the noble metal in the first step is performed based on at least one of the operation history, the gas temperature before and after the oxidation catalyst, the temperature of the oxidation catalyst, and the oxygen sensor output before and after the oxidation catalyst. (Corresponding to claim 2). In this case, a specific means for predicting the oxygen adsorption amount is provided.

The prediction of the oxygen adsorption amount of the noble metal based on the operation history is performed after the fuel cut (corresponding to claim 3). In this case, the oxygen adsorption amount of the noble metal of the oxidation catalyst by the fuel cut can be increased to a maximum state, the reduction of the scavenging or after et adsorption amount by the fuel cut can be accurately predicted.

The increase control of the oxygen adsorption amount of the precious metal in the second step, Oite during idle stop, by actuating the air pump, the oxidation catalyst are as carried out by scavenging with air (claim 4 correspondence). In this case, sufficient oxygen can be adsorbed to the oxidation catalyst using an air pump.

Wherein in the second step, the increase control of the oxygen adsorption amount of the noble metal, Oite during the idle stop, by opening the air tank that reservoir air, an oxidation catalyst is carried out by scavenging air, iodine (Corresponding to claim 5). In this case, the air previously stored in the air tank can be sufficiently supplied to the oxidation catalyst from the beginning.

Drive wheels are driven by both the engine and motor,
When the fuel is cut during traveling to increase the amount of oxygen adsorbed on the noble metal, the motor torque is corrected to increase so as to compensate for the reduction in engine torque that accompanies the fuel cut.
(Corresponding to claim 6 ). In this case, fuel can be cut during traveling to supply sufficient air for scavenging to the oxidation catalyst. In addition, the reduction in engine torque accompanying the fuel cut can be compensated by increasing the motor torque to ensure good drivability.

A third step of detecting the temperature of the oxidation catalyst;
When the temperature of the oxidation catalyst detected in the third step is equal to or lower than a predetermined temperature set in advance, the increase control of the oxygen adsorption amount to the noble metal in the second step is executed.
(Corresponding to claim 7 ). In this case, in a high temperature state where the oxidation catalyst is activated without scavenging, the increase in the amount of oxygen adsorption to the noble metal is not controlled, so that the execution time of the increase in the amount of oxygen adsorption is shortened as much as possible. This is preferable.

In order to achieve the above object, the following solution is adopted in the device of the present invention. That is, as described in claim 8 ,
An exhaust gas purification apparatus for an internal combustion engine having an oxidation catalyst in an exhaust system,
An oxygen adsorption amount prediction means for predicting the amount of oxygen adsorbed on the noble metal of the oxidation catalyst;
When the oxygen adsorption amount predicted by the oxygen adsorption amount prediction means is equal to or lower than a predetermined lower limit value set in advance, an increase control is performed to scavenge the noble metal of the oxidation catalyst and increase the oxygen adsorption amount to the noble metal. Means for increasing the amount of oxygen adsorbed on the noble metal;
Bei to give a,
The increase control for increasing the amount of oxygen adsorbed to the noble metal by the increase control means is to scavenge the noble metal of the oxidation catalyst with the high-temperature air discharged to the exhaust system without burning in the cylinder due to fuel cut during traveling Done by
It is like that. According to the above solution, an apparatus for executing the exhaust gas purification method for an internal combustion engine corresponding to claim 1 is provided.

  According to the present invention, it is not necessary to provide a separate heating means, or even if a separate heating means is provided, the operation time can be sufficiently shortened.

The figure which shows the example of a control system to which this invention was applied. Explanatory drawing which shows that an oxidation catalyst will be activated if the oxygen adsorption amount to a noble metal is enough. The figure which shows the change of the purification rate of the oxidation catalyst according to temperature and the amount of oxygen adsorption in the state where the amount of exhaust gas is high. The figure which shows the change of the purification rate of an oxidation catalyst according to temperature and the amount of oxygen adsorption in the state where the amount of exhaust gas is low. The time chart which shows the example of control of this invention. The flowchart for performing control like FIG. The figure which shows the drive system example in the case of driving a drive wheel with an engine and a motor. The time chart which shows an example which scavenges the noble metal of an oxidation catalyst by fuel cut, and performs the increase control which increases the oxygen adsorption amount to a noble metal. The flowchart for performing control like FIG.

  In FIG. 1, reference numeral 1 denotes an internal combustion engine, that is, an engine, and in the embodiment, an automobile diesel engine. The intake air is supplied from the intake passage 2 to the engine 1 through the intake manifold 3. Further, the exhaust gas from the engine 1 is released to the atmosphere through the exhaust manifold 4 and the exhaust passage 5. An oxidation catalyst 6 is disposed in the middle of the exhaust passage 5, and a DPF (diesel particulate filter) 7 is disposed on the downstream side of the oxidation catalyst 6. A scavenging passage 9 connected to the air pump 8 is connected to the exhaust passage 5 upstream of the oxidation catalyst 6.

  In FIG. 1, U is a controller (control unit) configured using a microcomputer. The controller U controls the air pump 8, and therefore, signals from various sensors S1 to S8 are input. The sensor S1 is an upstream oxygen sensor that detects the oxygen amount (oxygen concentration) upstream of the oxidation catalyst 6. The sensor S2 is a downstream oxygen sensor that detects the amount of oxygen downstream of the oxidation catalyst 6. The sensor S3 is a temperature sensor that detects the temperature of the oxidation catalyst 6. Sensors S4 and S5 are temperature sensors that detect gas temperatures before and after the oxidation catalyst, respectively. The sensor S6 is a rotation speed sensor that detects the engine rotation speed. The sensor S7 is a vehicle speed sensor that detects the vehicle speed. The sensor S8 is a brake sensor that detects that a brake (foot brake or parking brake) is operated.

  The controller U performs idle stop control for stopping the engine 1 when the vehicle is stopped and the brake is operated. When the oxidation catalyst 6 is lower than the predetermined activation temperature and the amount of adsorbed oxygen is small, the air pump 8 is operated to supply air from the scavenging passage 9 (scavenging execution). Increase oxygen adsorption on precious metals.

  As is well known, the oxidation catalyst 6 uses a noble metal such as platinum or palladium, but at a low temperature when the adsorptivity to the noble metal is high, highly adsorbable CO and the like are preferentially adsorbed and can adsorb oxygen. Insufficient free space. As a result, as shown in FIG. 2 (a), the amount of oxygen adsorbed on the noble metal is reduced, and the oxidation action cannot be sufficiently exhibited. On the other hand, in a state where the amount of oxygen adsorbed by the noble metal is large, as shown in FIG. 2B, the function of oxidizing unburned components such as CO until the adsorbed oxygen disappears is exhibited even at a low temperature. . In FIG. 2, PGM indicates a noble metal.

  FIG. 3 shows the change in the purification rate according to the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 in a state where the amount of exhaust gas is high (large). The solid line in the figure shows the normal purification characteristics and the purification rate when heating and increase control are not performed. As the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 increases, the purification rate increases even at low temperatures, as indicated by the one-dot chain line and two-dot chain line in the figure, and the purification rate increases as the oxygen adsorption amount increases. FIG. 4 is a diagram corresponding to FIG. 3 in a state where the amount of exhaust gas is low (small). Also in this case, the purification rate increases as the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 increases.

  Compared with FIGS. 3 and 4, the smaller the exhaust gas amount, the higher the purification rate increasing effect due to the increased oxygen adsorption amount with the noble metal of the oxidation catalyst 6. That is, in a situation where the amount of exhaust gas is small and it is difficult to raise the oxidation catalyst 6 to the activation temperature depending on the exhaust gas temperature, increasing the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 improves the purification rate. It is understood that this is very suitable.

  FIG. 5 shows a control example in which the oxygen adsorption amount increase control with the noble metal of the oxidation catalyst 6 is performed at the idle stop timing when the driving state and the idle stop are repeated. That is, the time point t1 is a time point when the idling stop is started, and traveling is performed before that time point. As the vehicle travels before time t1, the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 gradually decreases, and the amount of oxygen adsorbed is extremely reduced at time t1.

  When the idle stop is started at time t1, the air pump 8 is operated, and the air from the scavenging passage 9 is supplied from the exhaust passage 5 to the upstream side of the oxidation catalyst 6 and scavenged. Thereby, CO, NOx, HC, etc. on the noble metal are desorbed and oxygen is adsorbed instead, so that the amount of oxygen adsorbed on the noble metal of the oxidation catalyst 6 is rapidly increased. At time t2 when the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 reaches the upper limit, the operation of the air pump 8 is stopped. Traveling is started again at time t3 after t2, and accordingly, the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 is gradually reduced. The idle stop is performed again at time t4 after time t3. However, at time t4, the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 is still large, so the air pump 8 is not operated.

  Even in the low temperature state, the temperature of the oxidation catalyst 6 is quickly raised by the oxidation reaction heat in the oxidation catalyst 6 having a sufficient oxygen adsorption amount of the noble metal. In addition, in the engine that is made highly efficient, the temperature of the oxidation catalyst 6 is activated because the exhaust gas temperature is low in both the diesel engine and the gasoline engine (particularly those that are lean-burned leaner than the stoichiometric air-fuel ratio). In many cases, the temperature becomes lower than the crystallization temperature, and this tendency becomes remarkable at light load. Therefore, it is particularly suitable to apply the present invention to such a high efficiency engine.

  FIG. 6 shows a flowchart for performing the control as shown in FIG. 5, and this flowchart will be described below. In the following description, Q indicates a step. First, in Q1, signals from the sensors S1 to S8 are read. After Q1, in Q2, it is determined whether or not the temperature of the oxidation catalyst 6 detected by the sensor S3 is equal to or lower than a predetermined temperature (activation temperature, 150 ° C. in the embodiment). If the determination in Q2 is NO, the control returns to Q1, assuming that it is unnecessary to control the increase in the amount of adsorbed oxygen by scavenging noble metal using the air pump 8.

  If the determination in Q2 is YES, it is determined in Q3 whether or not an idle stop is being performed. Even when the determination in Q3 is NO, the control returns to Q1, assuming that it is not necessary to control the increase in the amount of adsorbed oxygen of the noble metal by scavenging using the air pump 8.

  If YES in Q3, the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 is estimated (predicted) in Q4. In the embodiment, the oxygen adsorption amount is estimated by comparing the outputs of the two oxygen sensors S1 and S2 upstream and downstream of the oxidation catalyst 6 (the smaller the difference between the outputs of S1 and S2, the oxidation reaction becomes). Is not progressing, and it can be determined that the oxygen adsorption amount is small).

  After Q4, in Q5, it is determined whether or not the oxygen adsorption amount of the noble metal estimated in Q4 is equal to or less than a predetermined lower limit set in advance. If NO in the determination of Q5, the oxygen adsorption amount of the noble metal of the oxidation catalyst 6 is large, so the process returns to Q1 at this time as well.

  When the determination in Q5 is YES, in Q6, the air pump 8 is operated, and the control for increasing the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 by scavenging is executed. The increase control of the oxygen adsorption amount may be executed for a certain predetermined time, or may be executed for a time corresponding to the oxygen adsorption amount estimated in Q4 (the execution time decreases as the oxygen adsorption amount decreases). And so on until the output difference between the oxygen sensors S1 and S2 exceeds a predetermined value.

  FIGS. 7 to 9 show a second embodiment of the present invention, and are based on the assumption that the vehicle can drive the drive wheels by both the engine and the motor. In the present embodiment, while the engine is running, the fuel is cut to increase the amount of oxygen adsorbed by the noble metal of the oxidation catalyst, and the torque reduction due to the fuel cut is compensated by the increase in the torque of the motor. .

  First, referring to FIG. 7, the output of the engine 1 is transmitted from the power split mechanism 11 configured using, for example, a planetary gear mechanism to the left and right drive drive wheels 14L and 14R via the gear 12 and the differential gear 13. Is done. Further, the output of the motor 15 is transmitted to the gear 12. Thereby, driving by only the engine 1, driving by only the motor 15, and driving by both the engine 1 and the motor 15 can be appropriately selected.

  Both the torque from the engine 1 and the torque from the motor 15 can be input to the power split mechanism 11, and the generator 16 is driven (power is generated) by the power split by the power split mechanism 11. The electric power generated by the generator 16 is charged to the high voltage battery 18 via the inverter 17. In addition, the electric power stored in the high voltage battery 18 is supplied to the motor 15 via the inverter 17.

  FIG. 8 shows a fuel cut during traveling in which the drive wheels 14L and 14R are driven by both the engine 1 and the motor 15 (in the embodiment, the vehicle is traveling in steady operation with constant engine rotation and constant vehicle speed). And a time chart when the motor torque increase correction is performed. First, until the time point t11, the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 gradually decreases as the vehicle travels, and the amount of oxygen adsorption reaches a predetermined lower limit value at the time point t11.

  At time t11, a fuel cut is performed so that scavenging of the noble metal of the oxidation catalyst 6 is executed, and the torque of the motor 15 is corrected to increase so as to compensate for a decrease in engine torque accompanying the fuel cut. By scavenging the oxidation catalyst with the air exhausted to the exhaust system without burning in the cylinder by cutting the fuel, CO, etc., preferentially adsorbed on the noble metal is desorbed, and oxygen in the air is replaced instead. By adsorbing, the oxygen adsorption amount of the noble metal of the oxidation catalyst 6 is increased. Note that air supply (scavenging) to the oxidation catalyst 6 accompanying the fuel cut is performed after a control delay such as control determination, and correction for increasing the motor torque is started in synchronization with the fuel cut.

  Due to the fuel cut, the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 gradually increases, and reaches a predetermined upper limit at time t12. At time t12, the fuel cut is stopped and the torque increase correction of the motor 15 is also stopped.

  By continuing further running from time t12, the oxygen adsorption amount of the noble metal of the oxidation catalyst 6 gradually decreases, and at time t13, the oxygen adsorption amount of the noble metal of the oxidation catalyst 6 becomes the predetermined lower limit value again. As a result, fuel cut and motor torque increase correction are performed again. Then, at time t14 when the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 reaches a predetermined upper limit value, both the fuel cut stop and the motor torque increase correction are stopped.

  A flowchart for performing the control as shown in FIG. 8 is shown in FIG. 9, which will be described below. First, in Q11, signals from the sensors S1 to S8 are read. After Q11, in Q12, it is determined whether or not the temperature of the oxidation catalyst 6 detected by the sensor S3 is equal to or lower than a predetermined temperature (activation temperature, 125 ° C. in the embodiment). If the determination in Q12 is NO, the process returns to Q11.

  If YES in Q12, the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 is estimated (predicted) in Q13 (corresponding to Q4 in FIG. 6). After Q13, in Q14, it is determined whether or not the oxygen adsorption amount estimated in Q13 is equal to or lower than a preset lower limit value. If the determination in Q14 is NO, the process returns to Q11.

  If YES in Q15, it is determined in Q15 whether or not the vehicle is running at least using the driving force of the engine 1. The driving travel by the motor 15 may be performed or may not be performed. If YES in Q15, the fuel cut is executed in Q16. Subsequently, in Q17, the torque of the motor 15 is corrected to increase so as to compensate for the decrease in engine torque accompanying the fuel cut.

  After Q17, in Q18, it is determined whether or not the oxygen adsorption amount of the oxidation catalyst 6 to the noble metal (new estimated value based on the outputs of the oxygen sensors S1 and S2) is equal to or greater than a predetermined upper limit value. If NO in Q18, the process returns to Q16. If YES in Q18, the fuel cut is stopped and the motor torque increase correction is stopped in Q19.

  When the determination in Q15 is NO, in Q20, as in the case of the above embodiment, the control for increasing the amount of oxygen adsorbed by the oxidation catalyst 6 by operating the air pump 8 is executed.

  Although the embodiment has been described above, the present invention is not limited to the embodiment, and can be appropriately changed within the scope described in the scope of claims. For example, the invention includes the following cases. . As long as it exhausts HC and CO in exhaust gas, such as a gasoline engine as well as a diesel engine, an appropriate engine can be applied to the present invention. Control of increase in the amount of adsorbed oxygen by fuel cut may be performed while a vehicle that does not have a drive motor for driving wheels is running. The prediction (estimation) of the amount of oxygen adsorbed by the noble metal of the oxidation catalyst 6 can be performed by various methods, for example, based on the operation history (particularly the progress state after scavenging such as fuel cut) or The prediction can be performed based on the temperature of the oxidation catalyst 6, and the prediction can be performed by combining a plurality of prediction means.

  An air tank is connected to the scavenging passage 9, and air in a predetermined pressure range is always stored in the air tank (air storage by an air pump). When the oxygen adsorption amount of the noble metal of the oxidation catalyst 6 decreases, the air tank is opened. Thus, the air in the air tank may be supplied to the oxidation catalyst 6. Further, a bypass path and an on-off valve may be provided in the scavenging passage 5 to bypass the exhaust gas that passes through the oxidation catalyst when scavenging is performed. Although the control according to the present invention is executed when the oxidation catalyst 6 is below the activation temperature, the control according to the present invention may be executed regardless of the temperature of the oxidation catalyst 6. Of course, the object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

  The present invention is preferable for exhaust gas purification utilizing an oxidation catalyst.

1: Engine 2: Intake passage 5: Exhaust passage 6: Oxidation catalyst 7: DPF
8: Air pump 15: Motor 16: Generator 17: Inverter 18: High voltage battery 14L: 14R: Drive wheel

Claims (8)

An exhaust gas purification method for an internal combustion engine having an oxidation catalyst in an exhaust system,
A first step of predicting the amount of oxygen adsorbed on the noble metal of the oxidation catalyst;
When the oxygen adsorption amount predicted in the first step is less than or equal to a predetermined lower limit set in advance, second control for scavenging the noble metal of the oxidation catalyst and increasing the oxygen adsorption amount on the noble metal is executed. Steps,
Bei to give a,
The increase control of the oxygen adsorption amount to the noble metal in the second step is performed by scavenging the noble metal of the oxidation catalyst with the high-temperature air discharged to the exhaust system without burning in the cylinder due to the fuel cut during traveling. Done,
An exhaust gas purification method for an internal combustion engine. In claim 1,
The prediction of the amount of oxygen adsorbed to the noble metal in the first step is performed based on at least one of the operation history, the gas temperature before and after the oxidation catalyst, the temperature of the oxidation catalyst, and the oxygen sensor output before and after the oxidation catalyst. An exhaust gas purification method for an internal combustion engine characterized by the above. In claim 2,
An exhaust gas purification method for an internal combustion engine, wherein the oxygen adsorption amount of the noble metal based on the operation history is predicted after the fuel cut. In claim 1,
An internal combustion engine control for increasing the oxygen adsorption amount of the precious metal in the second step is, Oite during idle stop, by actuating the air pump, an oxidation catalyst, characterized in that is carried out by scavenging with air Exhaust gas purification method. In claim 1,
Increase control of the oxygen adsorption amount of the noble metal in the second step is, Oite during idle stop, by opening the air tank that reservoir air, an oxidation catalyst is carried out by scavenging air, that An exhaust gas purification method for an internal combustion engine characterized by the above. In claim 1 ,
Drive wheels are driven by both the engine and motor,
When the fuel is cut during traveling to increase the amount of oxygen adsorbed on the noble metal, the motor torque is corrected to increase so as to compensate for the reduction in engine torque that accompanies the fuel cut.
An exhaust gas purification method for an internal combustion engine. In any one of Claims 1 thru | or 6 ,
A third step of detecting the temperature of the oxidation catalyst;
When the temperature of the oxidation catalyst detected in the third step is equal to or lower than a predetermined temperature set in advance, an increase control of the oxygen adsorption amount to the noble metal in the second step is executed.
An exhaust gas purification method for an internal combustion engine. An exhaust gas purification apparatus for an internal combustion engine having an oxidation catalyst in an exhaust system,
An oxygen adsorption amount prediction means for predicting the amount of oxygen adsorbed on the noble metal of the oxidation catalyst;
When the oxygen adsorption amount predicted by the oxygen adsorption amount prediction means is equal to or lower than a predetermined lower limit value set in advance, an increase control is performed to scavenge the noble metal of the oxidation catalyst and increase the oxygen adsorption amount to the noble metal. Means for increasing the amount of oxygen adsorbed on the noble metal;
Bei to give a,
The increase control for increasing the amount of oxygen adsorbed to the noble metal by the increase control means is to scavenge the noble metal of the oxidation catalyst with the high-temperature air discharged to the exhaust system without burning in the cylinder due to fuel cut during traveling Done by
An exhaust gas purification apparatus for an internal combustion engine, characterized in that:

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