JP2024110445A - Hybrid vehicle control method and hybrid vehicle control device - Google Patents

Abstract

To improve NOx treatment capacity of an NOx trap catalyst.SOLUTION: When performing desorption reduction treatment of NOx adsorbed to an NOx trap catalyst by making an air-fuel ratio richer than a theoretical air-fuel ratio, a hybrid vehicle performs torque reduction treatment for causing torque of an internal combustion engine to be lower than toque during a lean operation, so as to cause an intake air amount to be lower than an air amount that can obtain the same torque as that during the lean operation. The hybrid vehicle can secure a reaction time of the catalyst by reducing an exhaust gas flow rate when performing the desorption reduction treatment of the NOx trap catalyst, and can improve the NOx desorption reduction treatment and a treatment rate of other exhaust gas components (HC, CO, etc.) excluding NOx discharged during the desorption reduction treatment.SELECTED DRAWING: Figure 5

Description

The present invention relates to a control method for a hybrid vehicle and a control device for a hybrid vehicle.

For example, Patent Document 1 discloses a technology that enriches the air-fuel ratio of an internal combustion engine by reducing the amount of intake air when reducing and releasing NOx (nitrogen oxides) stored in a NOx trap catalyst (nitrogen oxide storage and reduction catalyst).

In Patent Document 1, the amount of intake air is reduced to enrich the air-fuel ratio, thereby suppressing the torque step that occurs when the NOx stored in the NOx trap catalyst is reduced and released.

Japanese Patent Application Publication No. 10-184418

However, Patent Document 1 does not take into consideration the improvement of the NOx processing capacity when reducing and releasing the NOx stored in the NOx trap catalyst, and there is room for further improvement in this regard.

The hybrid vehicle of the present invention is characterized in that, when the air-fuel ratio of the internal combustion engine is made leaner than the theoretical air-fuel ratio during lean operation, and NOx desorption/reduction processing is performed using a NOx trap catalyst by making the air-fuel ratio richer than the theoretical air-fuel ratio, the amount of intake air of the internal combustion engine is reduced below the amount of air that provides the same torque as during lean operation.

According to the present invention, by reducing the flow rate of exhaust gas when performing desorption/reduction processing, it is possible to ensure the reaction time of the catalyst during desorption/reduction processing. Therefore, hybrid vehicles can improve the processing rate of NOx desorption/reduction processing and other exhaust gas components (HC, CO, etc.) other than NOx that are emitted during desorption/reduction processing.

1 is an explanatory diagram showing a schematic overview of a system configuration of a hybrid vehicle to which the present invention is applied; FIG. 4 is a characteristic diagram showing the correlation between the residual rate of NOx and the value obtained by dividing the catalyst capacity by the exhaust gas flow rate. FIG. 4 is a characteristic diagram showing the correlation between the residual rate of NOx and rich time. FIG. 4 is a characteristic diagram showing the correlation between the amount of HC in the exhaust gas and rich time. 5 is a timing chart showing changes in various parameters during rich spike control in the first embodiment. 5 is a characteristic diagram showing the correlation between the amount of NOx adsorbed in the NOx trap catalyst at the start of NOx desorption processing and the command reduction torque during NOx processing; 10 is a timing chart showing changes in various parameters during rich spike control in the second embodiment. 4 is a characteristic diagram showing the correlation between the torque of the internal combustion engine, which is set at the start of the torque reduction process, and the NOx trapping capacity of the NOx trap catalyst; 4 is a characteristic diagram showing the correlation between the NOx trapping capacity of a NOx trap catalyst and catalyst deterioration of the NOx trap catalyst; 4 is a characteristic diagram showing the correlation between the NOx trapping capacity of a NOx trap catalyst and the catalyst temperature of the NOx trap catalyst; 13 is a timing chart showing changes in various parameters during rich spike control in the third embodiment. FIG. 4 is an explanatory diagram showing a schematic correlation between the catalyst outlet NOx amount and the NOx trap amount.

Below, one embodiment of the present invention will be described in detail with reference to the drawings.

Figure 1 is an explanatory diagram that shows a schematic overview of the system configuration of a hybrid vehicle to which the present invention is applied.

The internal combustion engine 1 is, for example, a spark-ignition type internal combustion engine that uses gasoline as fuel, and is mounted on a hybrid vehicle (not shown). The hybrid vehicle is capable of driving drive wheels (not shown) even when the internal combustion engine 1 is stopped, and is, for example, a series hybrid in which the internal combustion engine 1 is used for generating electricity. Note that the hybrid vehicle to which the present invention is applied may also be a parallel hybrid vehicle that has the internal combustion engine 1 and a traction motor as the drive source for the drive wheels.

The internal combustion engine 1 has a three-way catalyst 3 and a NOx trap catalyst (LNT) 4 in the exhaust passage 2. The three-way catalyst 3 is located upstream of the NOx trap catalyst 4 in the exhaust flow direction. The three-way catalyst 3 can simultaneously purify NOx, HC, and CO in the exhaust with maximum conversion efficiency when the air-fuel ratio is in a so-called window centered on the theoretical air-fuel ratio (λ=1).

The NOx trap catalyst 4 adsorbs (traps) NOx (nitrogen oxides) in the exhaust when the exhaust air-fuel ratio is lean, and reduces and purifies the adsorbed NOx using HC (hydrocarbons) and CO in the exhaust as reducing agents when the exhaust air-fuel ratio is stoichiometric or rich. In other words, the NOx trap catalyst 4 adsorbs NOx in the exhaust when the exhaust is in a lean atmosphere with excess oxygen, and desorbs and reduces NOx using HC and other reducing agents in the exhaust when the oxygen concentration is low and in a rich atmosphere.

The exhaust passage 2 is provided with an air-fuel ratio sensor 5 and an oxygen sensor 6. The air-fuel ratio sensor 5 is disposed upstream of the three-way catalyst 3. In other words, the air-fuel ratio sensor 5 detects the air-fuel ratio of the exhaust gas at the inlet side of the three-way catalyst 3. The air-fuel ratio sensor 5 has an output characteristic that is approximately linear according to the air-fuel ratio. The oxygen sensor 6 is disposed downstream of the three-way catalyst 3 and upstream of the NOx trap catalyst 4. The oxygen sensor 6 detects only whether the exhaust gas air-fuel ratio is rich or lean. In other words, the oxygen sensor 6 detects whether the exhaust gas air-fuel ratio is rich or lean at the outlet side of the three-way catalyst 3.

The internal combustion engine 1 also includes various sensors, such as a crank angle sensor 7 that detects the crank angle of the crankshaft (not shown) and an accelerator opening sensor 8 that detects the amount of depression of the accelerator pedal operated by the driver. The crank angle sensor 7 is capable of detecting the engine speed of the internal combustion engine 1.

The detection signals from the various sensors mentioned above are input to the control unit 9.

The control unit 9 is a well-known digital computer equipped with a CPU, ROM, RAM and an input/output interface.

The control unit 9 optimally controls the throttle opening of the internal combustion engine 1, the air-fuel ratio of the internal combustion engine 1, the amount of intake air of the internal combustion engine 1, etc., based on detection signals from various sensors. The throttle opening of the internal combustion engine 1 is the opening of a throttle valve (not shown) provided in the intake passage (not shown) of the internal combustion engine 1.

When the amount of NOx adsorbed in the NOx trap catalyst 4 (NOx trap amount) reaches a preset value, the control unit 9 as a control unit performs rich spike control to make the exhaust air-fuel ratio richer than the theoretical air-fuel ratio in order to desorb and reduce the NOx adsorbed in the NOx trap catalyst 4.

By implementing the rich spike control described above, the NOx adsorbed in the NOx trap catalyst 4 is desorbed and reduced using HC and other substances in the exhaust as reducing agents.

Figure 2 is a characteristic diagram showing the correlation between the remaining rate of NOx adsorbed in the NOx trap catalyst 4 and the value obtained by dividing the catalyst capacity of the NOx trap catalyst 4 by the exhaust gas flow rate flowing through the NOx trap catalyst 4 when the above-mentioned rich spike control is implemented.

The NOx residual rate of the NOx trap catalyst 4 decreases as the exhaust gas flow rate through the NOx trap catalyst 4 decreases relative to the catalyst capacity of the NOx trap catalyst 4. In other words, the NOx residual rate of the NOx trap catalyst 4 decreases as the exhaust gas flow rate during the above-mentioned rich spike control decreases. This is because the reduced exhaust gas flow rate allows more time for the catalytic reaction of the NOx trap catalyst 4. Note that the exhaust gas flow rate in this specification is a volumetric flow rate.

In addition, in order to prevent torque steps from occurring in the output of the internal combustion engine 1 during the rich spike control, it is necessary to control the amount of intake air so that the torque of the internal combustion engine 1 is equal before and after the rich spike control. For example, when the rich spike control is performed during lean operation (lean operation) in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the amount of intake air required differs between lean operation and rich operation during the rich spike control, so it is necessary to narrow the throttle valve opening to avoid torque fluctuations.

Figure 3 is a characteristic diagram showing the correlation between the remaining rate of NOx adsorbed in the NOx trap catalyst 4 and the rich time, which is the duration of the rich spike control. The solid line in Figure 3 shows the case where the intake air amount is controlled so that the torque of the internal combustion engine 1 during the rich spike control is lower than the torque of the internal combustion engine 1 before and after the rich spike control. The dashed line in Figure 3 shows the case where the intake air amount is controlled so that the torque of the internal combustion engine 1 during the rich spike control is equal to the torque of the internal combustion engine 1 before and after the rich spike control.

As shown by the solid line in Figure 3, if the intake air amount is controlled so that the torque of the internal combustion engine 1 during the rich spike control is lower than the torque of the internal combustion engine 1 before and after the rich spike control, it is possible to reduce the NOx residual rate regardless of the rich time.

Figure 4 is a characteristic diagram showing the correlation between the amount of HC in the exhaust gas during the rich spike control and the rich time, which is the duration of the rich spike control. The solid line in Figure 4 shows the case where the intake air amount is controlled so that the torque of the internal combustion engine 1 during the rich spike control is lower than the torque of the internal combustion engine 1 before and after the rich spike control. The dashed line in Figure 4 shows the case where the intake air amount is controlled so that the torque of the internal combustion engine 1 during the rich spike control is equal to the torque of the internal combustion engine 1 before and after the rich spike control.

As shown by the solid line in Figure 4, if the intake air volume is controlled so that the torque of the internal combustion engine 1 during the rich spike control is lower than the torque of the internal combustion engine 1 before and after the rich spike control, the HC supplied as a reducing agent is effectively used to convert the desorbed NOx, and the amount of HC discharged downstream of the NOx trap catalyst 4 is reduced.

Therefore, in the internal combustion engine 1 of the hybrid vehicle of the first embodiment, during the above-mentioned rich spike control, the intake air volume of the internal combustion engine 1 is reduced even further than the air volume that provides the same torque as during lean operation (lean operation).

In more detail, in the hybrid vehicle of the first embodiment, when the desorption and reduction process of NOx adsorbed in the NOx trap catalyst 4 is performed by increasing the fuel injection amount from the fuel injection valve (not shown) to make the air-fuel ratio richer than the theoretical air-fuel ratio, the torque of the internal combustion engine 1 is reduced to a torque reduction process lower than the torque during lean operation (lean operation), thereby reducing the intake air amount to a value lower than the air amount that provides the same torque as during lean operation (lean operation). In other words, when the desorption and reduction process of NOx adsorbed in the NOx trap catalyst 4 is performed by increasing the fuel injection amount from the fuel injection valve (not shown) to make the air-fuel ratio richer than the theoretical air-fuel ratio, the control unit 9 as a control unit reduces the intake air amount of the internal combustion engine 1 to a value lower than the air amount that provides the same torque as during lean operation (lean operation) by performing a torque reduction process lowering the torque of the internal combustion engine 1 to a value lower than the torque during lean operation (lean operation). The torque reduction process is performed in parallel with the desorption and reduction process. The start of the torque reduction process coincides with the start of the desorption reduction process. The end of the torque reduction process coincides with the end of the desorption reduction process.

Figure 5 is a timing chart showing the changes in various parameters during the rich spike control in the first embodiment. The solid lines in Figure 5 show the changes in various parameters during the rich spike control in the first embodiment. The dashed lines in Figure 5 are a comparative example showing a case where the intake air volume of the internal combustion engine 1 during the rich spike control is set to an air volume that provides the same torque as during lean operation.

Time t1 in Figure 5 is the timing when the amount of NOx adsorbed in the NOx trap catalyst 4 (NOx trap amount) reaches a predetermined amount and a NOx processing request, which is a request to implement the above-mentioned rich spike control, is established.

The amount of NOx adsorbed in the NOx trap catalyst 4 is calculated using a conventionally known calculation method. For example, the method for calculating the amount of NOx adsorbed in the NOx trap catalyst 4 may be the method described in JP-A-2003-293742, in which the amount of NOx adsorbed and the amount of NOx released per unit time or unit cycle are repeatedly added and subtracted to calculate the amount of NOx adsorbed in the NOx trap catalyst 4 at that time.

The air-fuel ratio (instructed air-fuel ratio) of the internal combustion engine 1 is switched from a predetermined lean air-fuel ratio that is leaner than the theoretical air-fuel ratio (λ=1) to a predetermined rich air-fuel ratio that is richer than the theoretical air-fuel ratio according to the air-fuel ratio instruction at the timing of time t1 in FIG. 5.

In the first embodiment, the torque of the internal combustion engine 1 is reduced by decreasing the throttle opening and reducing the exhaust gas flow rate at time t1 in FIG. 5 so that it is smaller than the torque during lean operation.

The amount of electricity generated by the generator (a generator driven by internal combustion engine 1) is also controlled to match the torque of each internal combustion engine.

Here, V1 in Figure 5 is the exhaust gas flow rate when the intake air amount is controlled so that the torque of the internal combustion engine 1 during the rich spike control is equal to the torque of the internal combustion engine 1 before and after the rich spike control.

In the first embodiment, the internal combustion engine 1 controls the throttle opening so that the exhaust gas flow rate is smaller than V1 at time t1 in FIG. 5.

Time t2 in Figure 5 is the timing when the amount of NOx adsorbed in the NOx trap catalyst 4 reaches a predetermined amount Ds in the comparative example. In the comparative example, at the timing of time t2 in Figure 5, the NOx processing request is not established, the air-fuel ratio (instructed air-fuel ratio) and throttle opening of the internal combustion engine 1 are switched to the state before time t1, and the exhaust gas flow rate is also returned to the state before time t1. In other words, in the comparative example, during the period from time t1 to t2 in Figure 5, the atmosphere of the exhaust flowing into the NOx trap catalyst 4 becomes richer than the theoretical air-fuel ratio, and desorption/reduction processing is performed in the NOx trap catalyst 4.

Time t3 in FIG. 5 is the timing when the amount of NOx adsorbed in the NOx trap catalyst 4 reaches a predetermined amount Ds in the hybrid vehicle of the first embodiment. In the internal combustion engine 1 of the first embodiment, at the timing of time t3 in FIG. 5, the NOx processing request is not satisfied, the air-fuel ratio (instructed air-fuel ratio) and throttle opening of the internal combustion engine 1 are switched to the state before time t1, and the exhaust gas flow rate is also returned to the state before time t1. In other words, in the first embodiment, during the period from time t1 to t3 in FIG. 5, the atmosphere of the exhaust flowing into the NOx trap catalyst 4 becomes richer than the theoretical air-fuel ratio, and desorption/reduction processing is performed in the NOx trap catalyst 4.

In the first embodiment, the internal combustion engine 1 is controlled so that the throttle opening gradually increases during the period from time t1 to time t3 in FIG. 5, so that the torque of the internal combustion engine 1 gradually increases and the exhaust gas flow rate gradually increases.

The internal combustion engine 1 in the first embodiment performs a torque reduction process that changes the amount of torque reduction in accordance with changes in the amount of NOx adsorbed in the NOx trap catalyst 4 during the period from time t1 to t3 in FIG. 5. In more detail, the internal combustion engine 1 in the first embodiment performs a torque reduction process that changes the amount of torque reduction so that the torque increases as the amount of NOx adsorbed in the NOx trap catalyst 4 decreases during the period from time t1 to t3 in FIG. 5.

In the first embodiment, the internal combustion engine 1 is controlled so that the air-fuel ratio gradually changes to the lean side during the period from time t1 to time t3 in FIG. 5 so that the air-fuel ratio becomes the theoretical air-fuel ratio at time t3 in FIG. 5.

As explained above, the internal combustion engine 1 in the hybrid vehicle of the first embodiment described above can ensure the catalyst's reaction time by reducing the exhaust gas flow rate when performing the desorption/reduction process of the NOx trap catalyst 4.

Therefore, the hybrid vehicle of the first embodiment can improve the treatment rate of NOx desorption/reduction and other exhaust gas components (HC, CO, etc.) other than NOx that are emitted during the desorption/reduction treatment.

The amount of NOx adsorbed to the NOx trap catalyst 4 during desorption/reduction processing is large at the start of the desorption/reduction processing and decreases over time. In other words, the amount of NOx desorbed from the NOx trap catalyst 4 during desorption/reduction processing (NOx desorption amount) is large at the start of the desorption/reduction processing and decreases over time. Therefore, the hybrid vehicle of the first embodiment changes the amount of torque reduction in the torque reduction processing in accordance with the change in the NOx trap amount or NOx desorption amount over time during the desorption/reduction processing.

As a result, the hybrid vehicle of the first embodiment can shorten the processing time of the NOx desorption/reduction process while ensuring the processing capacity of the NOx desorption/reduction process, and suppress the deterioration of fuel efficiency caused by performing the desorption/reduction process.

The hybrid vehicle of the first embodiment reduces the exhaust gas flow rate of the internal combustion engine 1 toward the first half of the desorption reduction process when the amount of NOx adsorbed on the NOx trap catalyst 4 becomes relatively large, so that the processing capacity of the NOx desorption reduction process can be efficiently ensured. In other words, the hybrid vehicle of the first embodiment reduces the exhaust gas flow rate of the internal combustion engine 1 toward the first half of the desorption reduction process when the amount of NOx desorbed from the NOx trap catalyst 4 becomes relatively large, so that the conversion rate of NOx desorbed from the NOx trap catalyst 4 is improved, so that the processing capacity of the NOx desorption reduction process can be efficiently ensured.

The hybrid vehicle of the first embodiment increases the exhaust gas flow rate of the internal combustion engine 1 toward the latter half of the desorption reduction process when the amount of NOx adsorbed on the NOx trap catalyst 4 becomes relatively small, so that the processing time of the NOx desorption reduction process can be shortened overall. In other words, the hybrid vehicle of the first embodiment increases the exhaust gas flow rate of the internal combustion engine 1 toward the latter half of the desorption reduction process when the amount of NOx desorbed from the NOx trap catalyst 4 becomes relatively small, so that the processing time of the NOx desorption reduction process can be shortened overall.

Below, we will explain another embodiment of the present invention. Note that the same components as those in the above-mentioned embodiment are given the same reference numerals and duplicate explanations will be omitted.

A hybrid vehicle according to a second embodiment of the present invention will be described with reference to Figures 6 and 7. The hybrid vehicle according to the second embodiment has substantially the same configuration as the hybrid vehicle according to the first embodiment described above, but is set so that the amount of torque reduction at the start of the torque reduction process varies depending on the amount of NOx adsorbed in the NOx trap catalyst 4. In more detail, the hybrid vehicle according to the second embodiment is set so that the greater the amount of NOx adsorbed in the NOx trap catalyst 4 at the start of the torque reduction process, the greater the amount of torque reduction in the internal combustion engine 1 at the start of the torque reduction process.

Figure 6 is a characteristic diagram showing the correlation between the amount of NOx adsorbed in the NOx trap catalyst at the start of NOx desorption processing and the command reduction torque during NOx processing. Note that the dashed line in Figure 6 is an example of the torque of the internal combustion engine 1 set during lean operation.

As shown in FIG. 6, in the hybrid vehicle of the second embodiment, the torque of the internal combustion engine 1 at the start of the torque reduction process is set to be smaller as the amount of NOx adsorbed in the NOx trap catalyst 4 at the start of the torque reduction process increases.

Figure 7 is a timing chart showing the changes in various parameters during the rich spike control in the second embodiment. The solid line in Figure 7 indicates the case where the amount of NOx adsorbed in the NOx trap catalyst 4 is large when the torque reduction process starts (for example, when the amount of adsorbed NOx is the maximum amount that can be adsorbed in the NOx trap catalyst 4). The dashed line in Figure 7 indicates the case where the amount of NOx adsorbed in the NOx trap catalyst 4 is small when the torque reduction process starts (for example, when the amount of adsorbed NOx is less than the maximum amount that can be adsorbed in the NOx trap catalyst 4).

Time t1 in Figure 7 is the timing when the amount of NOx adsorbed in the NOx trap catalyst 4 (NOx trap amount) reaches a predetermined amount and a NOx processing request, which is a request to implement the above-mentioned rich spike control, is established.

The air-fuel ratio (instructed air-fuel ratio) of the internal combustion engine 1 is switched from a predetermined lean air-fuel ratio that is leaner than the theoretical air-fuel ratio (λ=1) to a predetermined rich air-fuel ratio that is richer than the theoretical air-fuel ratio according to the air-fuel ratio instruction at the timing of time t1 in FIG. 7.

In the second embodiment, the throttle opening is reduced and the exhaust gas flow rate is decreased so that the torque of the internal combustion engine 1 is smaller than the torque during lean operation at time t1 in FIG. 7.

Here, V1 in Figure 7 is the exhaust gas flow rate when the intake air amount is controlled so that the torque of the internal combustion engine 1 during the rich spike control is equal to the torque of the internal combustion engine 1 before and after the rich spike control.

In the second embodiment, the internal combustion engine 1 controls the throttle opening so that the exhaust gas flow rate is smaller than V1 at time t1 in FIG. 7.

Time t2 in FIG. 7 is the timing at which the amount of NOx adsorbed in NOx trap catalyst 4 reaches a predetermined amount Ds in the hybrid vehicle of the second embodiment when the amount of NOx adsorbed in NOx trap catalyst 4 is small when the torque reduction process begins. If the amount of NOx adsorbed in NOx trap catalyst 4 is small when the torque reduction process begins, the NOx processing request is not established at time t2 in FIG. 7, the air-fuel ratio (instructed air-fuel ratio) and throttle opening of internal combustion engine 1 are switched to the state before time t1, and the exhaust gas flow rate is also returned to the state before time t1.

Time t3 in FIG. 7 is the timing at which the amount of NOx adsorbed in NOx trap catalyst 4 reaches a predetermined amount Ds in the hybrid vehicle of the second embodiment when the amount of NOx adsorbed in NOx trap catalyst 4 is large when the torque reduction process begins. If the amount of NOx adsorbed in NOx trap catalyst 4 is large when the torque reduction process begins, the NOx processing request is not established at time t3 in FIG. 7, the air-fuel ratio (instructed air-fuel ratio) and throttle opening of internal combustion engine 1 are switched to the state before time t1, and the exhaust gas flow rate is also returned to the state before time t1.

In other words, in the second embodiment where the amount of NOx adsorbed in NOx trap catalyst 4 is small when the torque reduction process begins, the atmosphere of the exhaust gas flowing into NOx trap catalyst 4 becomes richer than the theoretical air-fuel ratio during the period from t1 to t2 in FIG. 7, and desorption/reduction process is performed in NOx trap catalyst 4. In the second embodiment where the amount of NOx adsorbed in NOx trap catalyst 4 is large when the torque reduction process begins, the atmosphere of the exhaust gas flowing into NOx trap catalyst 4 becomes richer than the theoretical air-fuel ratio during the period from t1 to t3 in FIG. 7, and desorption/reduction process is performed in NOx trap catalyst 4.

When the amount of NOx adsorbed in the NOx trap catalyst 4 is small at the start of the torque reduction process, the internal combustion engine 1 in the second embodiment is controlled to gradually increase the throttle opening during the period from time t1 to t2 in FIG. 7, so that the torque gradually increases and the exhaust gas flow rate gradually increases. When the amount of NOx adsorbed in the NOx trap catalyst 4 is large at the start of the torque reduction process, the internal combustion engine 1 in the second embodiment is controlled to gradually increase the throttle opening during the period from time t1 to t3 in FIG. 7, so that the torque gradually increases and the exhaust gas flow rate gradually increases.

In the second embodiment, when the amount of NOx adsorbed by the NOx trap catalyst 4 is small at the start of the torque reduction process, the internal combustion engine 1 performs torque reduction processing during the period from time t1 to t2 in FIG. 7, which changes the amount of torque reduction so that the torque increases as the amount of NOx adsorbed by the NOx trap catalyst 4 decreases. In the second embodiment, when the amount of NOx adsorbed by the NOx trap catalyst 4 is large at the start of the torque reduction process, the internal combustion engine 1 performs torque reduction processing during the period from time t1 to t3 in FIG. 7, which changes the amount of torque reduction so that the torque increases as the amount of NOx adsorbed by the NOx trap catalyst 4 decreases.

When the amount of NOx adsorbed in the NOx trap catalyst 4 is small at the start of the torque reduction process, the internal combustion engine 1 in the second embodiment is controlled so that the air-fuel ratio gradually changes to the lean side during the period from time t1 to t2 in FIG. 7 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio at time t2 in FIG. 7. When the amount of NOx adsorbed in the NOx trap catalyst 4 is large at the start of the torque reduction process, the internal combustion engine 1 in the second embodiment is controlled so that the air-fuel ratio gradually changes to the lean side during the period from time t1 to t3 in FIG. 7 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio at time t3 in FIG. 7.

The hybrid vehicle of this second embodiment can achieve substantially the same effects as the hybrid vehicle of the first embodiment described above.

The amount of NOx processed by the torque reduction process decreases as the amount of NOx adsorbed in the NOx trap catalyst 4 (NOx trap amount) decreases. Therefore, the hybrid vehicle of the second embodiment changes the amount of torque reduction at the start of the torque reduction process depending on the amount of NOx adsorbed in the NOx trap catalyst 4.

As a result, the hybrid vehicle of the second embodiment can suppress deterioration of fuel efficiency of the internal combustion engine 1.

In more detail, in the hybrid vehicle of the second embodiment, the torque reduction amount in the torque reduction process increases the more NOx is adsorbed in the NOx trap catalyst 4 at the start of the desorption reduction process. In the hybrid vehicle of the second embodiment, the torque increases as the amount of NOx adsorbed in the NOx trap catalyst 4 decreases due to the torque reduction process, and the exhaust gas flow rate of the internal combustion engine 1 increases. Therefore, in the desorption reduction process of the second embodiment, the less NOx is adsorbed in the NOx trap catalyst 4, the shorter the NOx processing time becomes.

In other words, the hybrid vehicle of the second embodiment can optimize the NOx processing time in the desorption reduction process according to the amount of NOx adsorbed in the NOx trap catalyst 4, and can generally suppress the deterioration of fuel economy caused by performing the desorption reduction process.

A hybrid vehicle according to a third embodiment of the present invention will be described with reference to Figures 8 to 12. The hybrid vehicle according to the third embodiment has substantially the same configuration as the hybrid vehicle according to the first embodiment described above, but the amount of torque reduction in the torque reduction process is set to change according to the decrease in the NOx trapping capacity (NOx adsorption capacity) of the NOx trap catalyst 4. In more detail, the hybrid vehicle according to the third embodiment is set so that the amount of torque reduction in the torque reduction process increases as the NOx trapping capacity of the NOx trap catalyst 4 decreases.

Figure 8 is a characteristic diagram showing the correlation between the torque of the internal combustion engine 1, which is set at (just before) the start of the torque reduction process, and the NOx trapping capacity of the NOx trap catalyst 4. The horizontal axis of Figure 8 is the value obtained by dividing the amount of NOx adsorbed in the NOx trap catalyst 4 (NOx trap amount) at (just before) the start of the torque reduction process by the NOx trapping capacity of the NOx trap catalyst 4. The dashed line in Figure 8 is an example of the torque of the internal combustion engine 1, which is set during lean operation.

As shown in FIG. 8, in the hybrid vehicle of the third embodiment, the value on the horizontal axis increases as the NOx trapping capacity of the NOx trap catalyst 4 decreases, and the torque of the internal combustion engine 1 at the start of the torque reduction process is set to decrease.

The NOx trapping capacity of the NOx trap catalyst 4 depends on, for example, the catalyst deterioration of the NOx trap catalyst 4 and the temperature of the NOx trap catalyst 4.

Specifically, the deterioration of the NOx trap catalyst 4 progresses due to a decrease in oxygen storage capacity and an increase in the amount of sulfur poisoning. In other words, the NOx trapping capacity of the NOx trap catalyst 4 decreases due to a decrease in oxygen storage capacity and an increase in the amount of sulfur poisoning, as shown in Figure 9. Figure 9 is a characteristic diagram showing the correlation between the NOx trapping capacity of the NOx trap catalyst 4 and the catalyst deterioration of the NOx trap catalyst 4.

In addition, as shown in Figure 10, the NOx trapping ability of the NOx trap catalyst 4 drops sharply when the temperature of the NOx trap catalyst 4 reaches or exceeds a predetermined temperature. Figure 10 is a characteristic diagram showing the correlation between the NOx trapping ability of the NOx trap catalyst 4 and the catalyst temperature of the NOx trap catalyst 4.

Figure 11 is a timing chart showing the changes in various parameters during the rich spike control in the third embodiment. The solid line in Figure 11 shows the case where the NOx trapping capacity of the NOx trap catalyst 4 is high when the torque reduction process starts. The dashed line in Figure 11 shows the case where the NOx trapping capacity of the NOx trap catalyst 4 is low when the torque reduction process starts.

In addition, the maximum amount of NOx that can be adsorbed by the NOx trap catalyst 4 is different in terms of control when the NOx trapping capacity of the NOx trap catalyst 4 is high and when the NOx trapping capacity of the NOx trap catalyst 4 is low. Basically, as shown in Figure 12, the maximum amount of NOx that can be adsorbed by the NOx trap catalyst 4 is determined so that NOx does not flow out downstream of the NOx trap catalyst 4.

Figure 12 is an explanatory diagram that shows a schematic diagram of the correlation between the catalyst outlet NOx amount and the NOx trap amount when the amount of NOx flowing into the NOx trap catalyst 4 (catalyst inflow NOx amount) is constant. The catalyst outlet NOx amount is the amount of NOx flowing out of the NOx trap catalyst 4.

The maximum amount of NOx that can be adsorbed by the NOx trap catalyst 4 is set with a certain margin as shown in Figure 12 so that NOx does not flow out of the NOx trap catalyst 4.

In addition, in the hybrid vehicle of the third embodiment, the amount of torque reduction of the internal combustion engine 1 during the torque reduction process may be set based on the NOx trapping capacity of the NOx trap catalyst 4 and the ratio of the amount of NOx adsorbed in the NOx trap catalyst 4 at the start of the torque reduction process.

Time t1 in Figure 11 is the timing when the amount of NOx adsorbed in the NOx trap catalyst 4 (NOx trap amount) reaches a predetermined amount and a NOx processing request, which is a request to implement the above-mentioned rich spike control, is established.

The air-fuel ratio (instructed air-fuel ratio) of the internal combustion engine 1 is switched from a predetermined lean air-fuel ratio that is leaner than the theoretical air-fuel ratio (λ=1) to a predetermined rich air-fuel ratio that is richer than the theoretical air-fuel ratio according to the air-fuel ratio instruction at the timing of time t1 in FIG. 11.

In the third embodiment, the throttle opening is reduced and the exhaust gas flow rate is decreased so that the torque of the internal combustion engine 1 becomes smaller than the torque during lean operation at time t1 in FIG.
Furthermore, in the third embodiment, the amount of torque reduction at the start of the torque reduction process is less when the NOx trapping capacity of NOx trap catalyst 4 is in state A (solid line) than when the NOx trapping capacity of NOx trap catalyst 4 is in state B (dashed line).

Here, V1 in FIG. 11 is the exhaust gas flow rate when the intake air amount is controlled so that the torque of the internal combustion engine 1 during the rich spike control is equal to the torque of the internal combustion engine 1 before and after the rich spike control.

In addition, DH in FIG. 11 is the maximum amount of NOx that can be adsorbed when the state of the NOx trapping capacity of the NOx trap catalyst 4 is state A. DL in FIG. 11 is the maximum amount of NOx that can be adsorbed when the state of the NOx trapping capacity of the NOx trap catalyst 4 is state B.

In the third embodiment, the internal combustion engine 1 controls the throttle opening so that the exhaust gas flow rate is smaller than V1 at time t1 in FIG. 11.

Time t2 in FIG. 11 is the timing at which the amount of NOx adsorbed in NOx trap catalyst 4 reaches a predetermined amount Ds in the hybrid vehicle of the third embodiment when the NOx trapping capacity of NOx trap catalyst 4 is in state A when the torque reduction process begins. If the NOx trapping capacity of NOx trap catalyst 4 is in state A when the torque reduction process begins, the NOx processing request is not satisfied at time t2 in FIG. 11, the air-fuel ratio (instructed air-fuel ratio) and throttle opening of internal combustion engine 1 are switched to the state before time t1, and the exhaust gas flow rate is also returned to the state before time t1.

Time t3 in FIG. 11 is the timing at which the amount of NOx adsorbed in NOx trap catalyst 4 reaches a predetermined amount Ds in a hybrid vehicle of the third embodiment in which the NOx trapping capacity of NOx trap catalyst 4 is in state B when the torque reduction process begins. If the NOx trapping capacity of NOx trap catalyst 4 is in state B when the torque reduction process begins, the NOx processing request is not satisfied at time t3 in FIG. 11, the air-fuel ratio (instructed air-fuel ratio) and throttle opening of internal combustion engine 1 are switched to the state before time t1, and the exhaust gas flow rate is also returned to the state before time t1.

In other words, in the third embodiment where the state of the NOx trapping capacity of NOx trap catalyst 4 is in state A when the torque reduction process begins, the atmosphere of the exhaust gas flowing into NOx trap catalyst 4 becomes richer than the theoretical air-fuel ratio during the period from t1 to t2 in FIG. 11, and desorption/reduction process is performed in NOx trap catalyst 4. In the third embodiment where the state of the NOx trapping capacity of NOx trap catalyst 4 is in state B when the torque reduction process begins, the atmosphere of the exhaust gas flowing into NOx trap catalyst 4 becomes richer than the theoretical air-fuel ratio during the period from t1 to t3 in FIG. 11, and desorption/reduction process is performed in NOx trap catalyst 4.

When the state of the NOx trapping capacity of the NOx trap catalyst 4 is in state A at the start of the torque reduction process, the internal combustion engine 1 in the third embodiment is controlled to gradually increase the throttle opening during the period from time t1 to t2 in FIG. 11, so that the torque gradually increases and the exhaust gas flow rate gradually increases. When the state of the NOx trapping capacity of the NOx trap catalyst 4 is in state B at the start of the torque reduction process, the internal combustion engine 1 in the third embodiment is controlled to gradually increase the throttle opening during the period from time t1 to t3 in FIG. 11, so that the torque gradually increases and the exhaust gas flow rate gradually increases.

In the third embodiment, when the NOx trapping capacity of NOx trap catalyst 4 is in state A at the start of the torque reduction process, internal combustion engine 1 performs torque reduction processing during the period from time t1 to t2 in FIG. 11, which changes the amount of torque reduction so that the torque increases as the amount of NOx adsorbed by NOx trap catalyst 4 decreases. In the third embodiment, when the NOx trapping capacity of NOx trap catalyst 4 is in state B at the start of the torque reduction process, internal combustion engine 1 performs torque reduction processing during the period from time t1 to t3 in FIG. 11, which changes the amount of torque reduction so that the torque increases as the amount of NOx adsorbed by NOx trap catalyst 4 decreases.

When the state of the NOx trapping capacity of the NOx trap catalyst 4 is in state A at the start of the torque reduction process, the internal combustion engine 1 in the third embodiment is controlled so that the air-fuel ratio gradually changes to the lean side during the period from time t1 to t2 in FIG. 11 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio at time t2 in FIG. 11. When the state of the NOx trapping capacity of the NOx trap catalyst 4 is in state B at the start of the torque reduction process, the internal combustion engine 1 in the third embodiment is controlled so that the air-fuel ratio gradually changes to the lean side during the period from time t1 to t3 in FIG. 11 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio at time t3 in FIG. 11.

The hybrid vehicle of the third embodiment can achieve substantially the same effects as the hybrid vehicle of the first embodiment described above.

As the NOx trapping capacity of the NOx trap catalyst 4 decreases, NOx is also adsorbed downstream of the catalyst in the exhaust flow direction, and the desorption reduction process capacity also decreases due to deterioration.

Therefore, the hybrid vehicle of the third embodiment changes the amount of torque reduction in the torque reduction process according to the decrease in the NOx trapping capacity of the NOx trap catalyst 4.

As a result, the hybrid vehicle of the third embodiment can change the flow rate of exhaust gas in response to the decrease in trapping capacity, ensuring sufficient reaction time for the catalyst during desorption reduction processing, and suppressing the decrease in NOx processing performance during torque reduction processing.

In more detail, the hybrid vehicle of the third embodiment increases the amount of torque reduction in the torque reduction process as the NOx trapping capacity of the NOx trap catalyst 4 decreases, thereby reducing the flow rate of the exhaust gas, thereby ensuring the reaction time of the catalyst during the desorption reduction process and suppressing the decrease in NOx processing performance during the torque reduction process.

Although specific examples of the present invention have been described above, the present invention is not limited to the above examples, and various modifications are possible without departing from the spirit of the present invention.

For example, if the hybrid vehicle in each of the above-mentioned embodiments is a parallel hybrid vehicle having a traction motor that drives the drive wheels, the control unit 9 may compensate (assist) the torque with the traction motor during the above-mentioned rich spike control so that the torque is equal to that during lean operation (lean operation), thereby preventing the driver from feeling uncomfortable due to torque fluctuations.

The above-mentioned embodiments relate to a control method for a hybrid vehicle and a control device for a hybrid vehicle.

1 internal combustion engine 2 exhaust passage 3 three-way catalyst 4 NOx trap catalyst 5 air-fuel ratio sensor 6 oxygen sensor 7 crank angle sensor 8 accelerator opening sensor 9 control unit

Claims (9)

A method for controlling a hybrid vehicle having an internal combustion engine with a NOx trap catalyst disposed in an exhaust passage, the NOx trap catalyst trapping NOx in the exhaust gas when the exhaust gas is in a lean atmosphere with an excess of oxygen and desorbing and reducing the NOx when the exhaust gas is in a rich atmosphere with a reduced oxygen concentration, and capable of driving drive wheels even when the internal combustion engine is stopped, comprising:
A control method for a hybrid vehicle, characterized in that, when the desorption/reduction process is performed by making the air-fuel ratio richer than the stoichiometric air-fuel ratio during lean operation in which the air-fuel ratio of the internal combustion engine is leaner than the stoichiometric air-fuel ratio, an intake air amount of the internal combustion engine is reduced below an air amount that provides an equivalent torque to that during lean operation. The method for controlling a hybrid vehicle according to claim 1, characterized in that when the desorption-reduction process is performed during the lean operation, a torque reduction process is performed to reduce the torque of the internal combustion engine to a level lower than the torque during the lean operation. The hybrid vehicle control method according to claim 2, characterized in that the torque reduction process changes the amount of torque reduction in accordance with changes in the amount of NOx adsorbed in the NOx trap catalyst. The hybrid vehicle control method according to claim 3, characterized in that the torque reduction process varies the amount of torque reduction so that the torque increases as the amount of NOx adsorbed in the NOx trap catalyst decreases. The control method for a hybrid vehicle according to claim 2, characterized in that the torque reduction process varies the amount of torque reduction at the start of the torque reduction process depending on the amount of NOx adsorbed in the NOx trap catalyst. The hybrid vehicle control method according to claim 5, characterized in that the torque reduction process increases the amount of torque reduction at the start of the torque reduction process as the amount of NOx adsorbed in the NOx trap catalyst increases. The hybrid vehicle control method according to claim 2, characterized in that the torque reduction process varies the amount of torque reduction in response to the reduction in the NOx trapping capacity of the NOx trap catalyst. The hybrid vehicle control method according to claim 7, characterized in that the torque reduction process increases the amount of torque reduction as the NOx trapping capacity of the NOx trap catalyst decreases. A control device for a hybrid vehicle has an internal combustion engine in which a NOx trap catalyst is disposed in an exhaust passage, the NOx trap catalyst trapping NOx in the exhaust gas when the exhaust gas is in a lean atmosphere with an excess of oxygen and desorbing and reducing the NOx when the exhaust gas is in a rich atmosphere with a reduced oxygen concentration, and the vehicle can drive drive wheels even when the internal combustion engine is stopped,
A control device for a hybrid vehicle, comprising: a control unit that reduces an intake air amount of the internal combustion engine below an air amount that provides an equivalent torque as during lean operation, when the desorption/reduction process is performed by making the air-fuel ratio richer than the stoichiometric air-fuel ratio during lean operation in which the air-fuel ratio of the internal combustion engine is leaner than the stoichiometric air-fuel ratio.

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