Vehicle control method and vehicle control device

Abstract

This suppresses the deterioration of exhaust performance after the fuel cut-off operation ends. [Solution] When the fuel cut recovery conditions are met and fuel supply to the internal combustion engine 2 is resumed, the control unit 15 sets the oxygen storage amount of the upstream catalyst 4 and the oxygen storage amount of the downstream catalyst 5 to predetermined target values, and performs fuel cut post-operation control to control the air-fuel ratio of the internal combustion engine 2 so that the oxygen storage amounts of the upstream catalyst 4 and the downstream catalyst 5 reach predetermined target values. As a result, the vehicle 1 can maintain a sufficient level of purification capacity in the upstream catalyst 4 and the downstream catalyst 5 after the fuel cut operation is completed, thereby suppressing deterioration of exhaust performance after the fuel cut operation is completed.

Description

Technical Field

[0001] The present invention relates to a vehicle control method and a vehicle control device.

Background Art

[0002] For example, in Patent Document 1, in an internal combustion engine in which an upstream catalyst and a downstream catalyst are respectively arranged on the upstream side and the downstream side of an exhaust passage, a fuel cut operation for stopping the fuel supply to the internal combustion engine during deceleration operation is performed. When this fuel cut operation ends, a technique is disclosed in which the air-fuel ratio of the internal combustion engine is set to a richer air-fuel ratio than the theoretical air-fuel ratio until the oxygen storage amount of the downstream catalyst reaches a predetermined value.

[0003] When the internal combustion engine performs a fuel cut operation, a large amount of oxygen flows in, so the oxygen storage amount of the upstream catalyst and the downstream catalyst often reaches the maximum oxygen storage amount.

[0004] Therefore, in Patent Document 1, after the end of the fuel cut operation, a rich control after fuel cut return is performed in which the air-fuel ratio of the internal combustion engine is set to a richer air-fuel ratio than the theoretical air-fuel ratio until the oxygen storage amount of the downstream catalyst decreases to a predetermined value, suppressing the deterioration of exhaust performance after the end of the fuel cut operation.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in Patent Document 1, the rich control after fuel cut-off recovery only considers the oxygen storage capacity of the downstream catalyst, one of the two exhaust gas purification catalysts, and the oxygen storage capacity of the upstream catalyst is "0" when the rich control after fuel cut-off recovery is terminated.

[0007] Therefore, in Patent Document 1, if operating conditions continue to make the air-fuel ratio richer than the stoichiometric air-fuel ratio after the rich control has ended following the return of fuel cut, there is a risk that CO and HC in the exhaust gas will be released to the outside without being purified by the upstream and downstream catalysts.

[0008] In other words, in vehicles with two exhaust purification catalysts in the exhaust passage of the internal combustion engine, there is room for further improvement in suppressing the deterioration of exhaust performance after the fuel cut-off operation ends. [Means for solving the problem]

[0009] In this invention, a vehicle is equipped with a first catalyst and a second catalyst for exhaust gas purification in the exhaust passage of an internal combustion engine. When predetermined fuel cut conditions are met, the fuel supply to the internal combustion engine is stopped, and when predetermined fuel cut recovery conditions are met, the fuel supply to the internal combustion engine is resumed. When the fuel cut recovery conditions are met and the fuel supply to the internal combustion engine is resumed, the vehicle sets the oxygen storage amounts of the first catalyst and the second catalyst to predetermined target values, and controls the air-fuel ratio of the internal combustion engine so that the oxygen storage amounts of the first catalyst and the second catalyst reach these predetermined target values. [Effects of the Invention]

[0010] According to the present invention, compared to adjusting the oxygen storage amount of only one of the first or second catalyst after the fuel cut-off operation is completed, the emission of HC, CO, and NOx (concentration at the tailpipe opening) can be suppressed. [Brief explanation of the drawing]

[0011] [Figure 1]A schematic diagram illustrating the system configuration of a vehicle to which the present invention is applied. [Figure 2] A timing chart showing the changes in various parameters when control is implemented after the fuel cut-off period ends. [Modes for carrying out the invention]

[0012] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0013] Figure 1 is a schematic diagram illustrating the system configuration of vehicle 1 to which the present invention is applied.

[0014] Vehicle 1 is equipped with an internal combustion engine 2 to drive the drive wheels (not shown). In the exhaust passage 3 of the internal combustion engine 2, an upstream catalyst 4 and a downstream catalyst 5 for exhaust gas purification are arranged in series along the direction of exhaust gas flow.

[0015] The upstream catalyst 4 corresponds to the first catalyst and is a three-way catalyst. The upstream catalyst 4 is located upstream of the downstream catalyst 5 in the direction of exhaust flow. A three-way catalyst can simultaneously purify NOx, HC, and CO in the exhaust with maximum conversion efficiency when the air-fuel ratio is within the so-called window centered on the stoichiometric air-fuel ratio. The upstream catalyst 4 is, for example, a manifold catalyst installed in the collector section of the exhaust manifold.

[0016] The downstream catalyst 5 corresponds to the second catalyst and is a three-way catalyst. The downstream catalyst 5 is an underfloor catalyst, for example, located under the floor of the vehicle 1.

[0017] Furthermore, the exhaust passage 3 is equipped with an air-fuel ratio sensor 6 and an oxygen sensor 7. The air-fuel ratio sensor 6 is located upstream of the upstream catalyst 4. In other words, the air-fuel ratio sensor 6 detects the air-fuel ratio of the exhaust at the inlet side of the upstream catalyst 4. The air-fuel ratio sensor 6 has a substantially linear output characteristic according to the air-fuel ratio. The oxygen sensor 7 is located downstream of the downstream catalyst 5. The oxygen sensor 7 detects only the rich / lean state of the exhaust air-fuel ratio. In other words, the oxygen sensor 7 detects the rich / lean state of the exhaust air-fuel ratio at the outlet side of the downstream catalyst 5. Alternatively, a sensor of the same type as the air-fuel ratio sensor 6 may be placed downstream of the downstream catalyst 5 instead of the oxygen sensor 7.

[0018] Vehicle 1 is also equipped with various sensors, including an airflow meter 8 for detecting intake air volume, a crank angle sensor 9 for detecting the crank angle of the crankshaft (not shown), an accelerator opening sensor 10 for detecting the amount the accelerator pedal is pressed by the driver, a vehicle speed sensor 11 for detecting vehicle speed, a first temperature sensor 12 for detecting the temperature of the upstream catalyst 4, and a second temperature sensor 13 for detecting the temperature of the downstream catalyst 5. The crank angle sensor 9 is capable of detecting the engine speed of the internal combustion engine 2.

[0019] The detection signals from the various sensors mentioned above are input to the control unit 15.

[0020] The control unit 15 is a well-known digital computer equipped with a CPU, ROM, RAM, and an input / output interface. Based on detection signals from various sensors, the control unit 15 optimally controls the fuel injection amount and timing of the internal combustion engine 2, the ignition timing of the internal combustion engine 2, the intake air amount, and so on.

[0021] When a predetermined fuel cut condition is satisfied, the control unit 15 performs a fuel cut operation to stop the fuel supply to the internal combustion engine 2. The fuel cut condition is satisfied, for example, during deceleration when the engine speed is equal to or higher than a predetermined fuel cut speed and the accelerator opening is equal to or lower than a predetermined opening after the warm-up of the internal combustion engine 2 is completed. When a predetermined fuel cut recovery condition is satisfied during the fuel cut, the control unit 15 resumes the fuel supply to the internal combustion engine 2. The fuel cut recovery condition is satisfied, for example, when the accelerator opening becomes larger than the predetermined opening or when the engine speed becomes equal to or lower than a predetermined fuel cut recovery speed without stepping on the accelerator pedal.

[0022] The upstream catalyst 4 and the downstream catalyst 5, which are three-way catalysts, purify NOx in the exhaust gas by reducing NOx in the exhaust gas. That is, if the upstream catalyst 4 and the downstream catalyst 5 are in a state where they can take in oxygen (a state where there is a margin in the oxygen storage capacity), they can purify NOx in the exhaust gas by reducing the inflowing NOx and taking in oxygen.

[0023] In addition, the upstream catalyst 4 and the downstream catalyst 5 purify HC and CO in the exhaust gas by oxidizing HC and CO in the exhaust gas. That is, if the upstream catalyst 4 and the downstream catalyst 5 are in a state where they can release oxygen (a state where they are storing oxygen), they can purify HC and CO in the exhaust gas by oxidizing the inflowing HC and CO.

[0024] Here, when the fuel cut condition is satisfied and the fuel supply to the internal combustion engine 2 is stopped, a large amount of oxygen flows into the upstream catalyst 4 and the downstream catalyst 5, and there is a risk that the oxygen storage amounts of the upstream catalyst 4 and the downstream catalyst 5 reach the maximum value (become saturated).

[0025] Therefore, in order to ensure the exhaust gas purification performance of the upstream catalyst 4 and the downstream catalyst 5, it is desirable to maintain the oxygen storage amount within a predetermined range between 0 and the maximum value.

[0026] Therefore, when the fuel cut recovery conditions are met and fuel supply to the internal combustion engine 2 is resumed, the control unit 15 sets the oxygen storage amount of the upstream catalyst 4 and the oxygen storage amount of the downstream catalyst 5 to predetermined target values, and performs fuel cut post-completion control to control the air-fuel ratio of the internal combustion engine 2 so that the oxygen storage amounts of the upstream catalyst 4 and the downstream catalyst 5 are each at predetermined target values.

[0027] The oxygen storage amounts of the upstream catalyst 4 and the downstream catalyst 5 are calculated using detection signals from, for example, an air-fuel ratio sensor 6, an oxygen sensor 7, an airflow meter 8, etc.

[0028] After the fuel cut-off is completed, control is performed, for example, when the temperatures of the upstream catalyst 4 and the downstream catalyst 5 are above a predetermined temperature. Here, the predetermined temperature is, for example, the activation temperature of the upstream catalyst 4 and the downstream catalyst 5.

[0029] Figure 2 is a timing chart showing the changes in various parameters when control is performed after the fuel cut-off period ends.

[0030] Time t1 is the timing when the fuel cut condition is met and fuel cut operation of the internal combustion engine 2 begins. When fuel cut operation begins, the oxygen storage amount in the upstream catalyst 4 increases to its maximum value (100%), and then increases to its maximum value (100%) in the downstream catalyst 5.

[0031] Time t2 is the timing when the fuel cut recovery condition is met and the fuel cut operation of internal combustion engine 2 ends. In other words, time t2 is the timing when control starts after the fuel cut ends.

[0032] The fuel cut-off completion control is performed between time t2 and time t6 in Figure 2. Here, the fuel cut-off completion control consists of a first air-fuel ratio control that controls the oxygen storage amount of the downstream catalyst 5 to a predetermined target value Mdt, and a second air-fuel ratio control that controls the oxygen storage amount of the upstream catalyst 4 to a predetermined target value Mut. The second air-fuel ratio control is performed immediately after the completion of the first air-fuel ratio control.

[0033] The target value Mut for the oxygen storage amount of the upstream catalyst 4 is a value set within a first predetermined range (first window) that is greater than or equal to a predetermined first upstream predetermined value Mu1 and less than or equal to a predetermined second upstream predetermined value Mu2. In other words, the target value Mut for the oxygen storage amount of the upstream catalyst 4 is a value within the range defined by the first upstream predetermined value Mu1 and the second upstream predetermined value Mu2.

[0034] The first upstream predetermined value Mu1 is a value greater than or equal to the minimum oxygen storage capacity of the upstream catalyst 4 that allows the conversion rate (purification rate) of CO and HC in the exhaust to be kept within a predetermined regulatory range in which CO and HC in the exhaust can be purified. The second upstream predetermined value Mu2 is a value less than or equal to the maximum oxygen storage capacity of the upstream catalyst 4 that allows the conversion rate (purification rate) of NOx in the exhaust to be kept within a predetermined regulatory range in which NOx in the exhaust can be purified.

[0035] The target value Mdt for the oxygen storage amount of the downstream catalyst 5 is a value set within a second predetermined range (second window) that is greater than or equal to a predetermined first downstream predetermined value Md1 and less than or equal to a predetermined second downstream predetermined value Md2. In other words, the target value Mdt for the oxygen storage amount of the downstream catalyst 5 is a value within the range defined by the first downstream predetermined value Md1 and the second downstream predetermined value Md2.

[0036] The first downstream predetermined value Md1 is a value greater than or equal to the minimum oxygen storage capacity of the downstream catalyst 5 that allows the conversion rate (purification rate) of CO and HC in the exhaust to be kept within a predetermined regulatory range in which CO and HC in the exhaust can be purified. The second downstream predetermined value Md2 is a value less than or equal to the maximum oxygen storage capacity of the downstream catalyst 5 that allows the conversion rate (purification rate) of NOx in the exhaust to be kept within a predetermined regulatory range in which NOx in the exhaust can be purified.

[0037] The target value Mdt for the oxygen storage amount of the downstream catalyst 5 is, for example, the same value as the target value Mut for the oxygen storage amount of the upstream catalyst 4. The first predetermined value Md1 on the downstream side is, for example, the same value as the first predetermined value Mu1 on the upstream side. The second predetermined value Md2 on the downstream side is, for example, the same value as the second predetermined value Mu2 on the upstream side.

[0038] Furthermore, from time t2 onwards, the first air-fuel ratio control request flag is turned on because the fuel cut operation has ended. In other words, time t2 is the timing when the first air-fuel ratio control, which is controlled after the fuel cut ends, begins.

[0039] The first air-fuel ratio control sets the target air-fuel ratio of the internal combustion engine 2 to a first air-fuel ratio that is richer than the stoichiometric air-fuel ratio.

[0040] When the first air-fuel ratio control is initiated and the target air-fuel ratio of the internal combustion engine 2 is set to the first air-fuel ratio, the oxygen storage amount of the downstream catalyst 5 begins to decrease after the oxygen storage amount of the upstream catalyst 4 reaches "0 (%)".

[0041] Time t5 is the timing when the oxygen storage amount of the downstream catalyst 5 reaches the target value Mdt, the first air-fuel ratio control request flag is turned off, and the first air-fuel ratio control ends. The oxygen storage amount of the upstream catalyst 4 reaches its minimum value (0%) at time t4, prior to the timing when the oxygen storage amount of the downstream catalyst 5 reaches the target value Mdt. Note that time t3 is the timing when the oxygen storage amount of the upstream catalyst 4 decreases to the target value Mut during the first air-fuel ratio control.

[0042] Furthermore, time t5 is also the timing when the flag requesting the second air-fuel ratio control is turned on because the first air-fuel ratio control has finished. In other words, time t5 is the timing when the second air-fuel ratio control, which is controlled after the fuel cut-off has ended, begins.

[0043] The second air-fuel ratio control sets the target air-fuel ratio of the internal combustion engine 2 to a second air-fuel ratio that is leaner than the stoichiometric air-fuel ratio.

[0044] By starting the second air-fuel ratio control and setting the target air-fuel ratio of the internal combustion engine 2 to the second air-fuel ratio, it is possible to increase the oxygen storage amount of the upstream catalyst 4 while keeping the oxygen storage amount of the downstream catalyst 5 constant.

[0045] Time t6 is the moment when the oxygen storage amount in the upstream catalyst 4 reaches the target value Mut, the second air-fuel ratio control request flag is turned off, and the second air-fuel ratio control ends.

[0046] In the vehicle 1 of the above-described embodiment, when the fuel cut-recovery condition is met and fuel supply to the internal combustion engine 2 is resumed, the air-fuel ratio (equivalent ratio) of the internal combustion engine 2 is controlled so that the oxygen storage amounts of the upstream catalyst 4 and the downstream catalyst 5 reach the target value. In other words, in the vehicle 1 of the above-described embodiment, when the fuel cut-recovery condition is met and fuel supply to the internal combustion engine 2 is resumed, the air-fuel ratio is controlled so that both the upstream catalyst 4 and the downstream catalyst 5 are in a state where exhaust gas purification can be performed efficiently.

[0047] As a result, after the fuel cut-off operation ends, vehicle 1 can maintain sufficient purification capacity for the upstream catalyst 4 and the downstream catalyst 5, thereby suppressing deterioration of exhaust performance after the fuel cut-off operation ends.

[0048] Furthermore, compared to the case where only the oxygen storage amount of the upstream catalyst 4 and the downstream catalyst 5 is adjusted after the fuel cut operation is completed, vehicle 1 can suppress the emission of HC, CO, and NOx (concentration at the tailpipe opening).

[0049] Although specific embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0050] For example, after the fuel cut-off is completed, if the upstream catalyst 4 is activated and the downstream catalyst 5 is deactivated, the air-fuel ratio of the internal combustion engine 2 may be controlled so that the oxygen storage amount of only the upstream catalyst 4 reaches the target value. Specifically, if the upstream catalyst 4 is activated and the downstream catalyst 5 is deactivated, the fuel cut-off is completed by operating the internal combustion engine 2 at a first air-fuel ratio that is richer than stoichiometric, and ending when the oxygen storage amount of the upstream catalyst 4 reaches a predetermined target value Mut (for example, at time t3 in Figure 2).

[0051] As a result, after the fuel cut-off operation ends, if the upstream catalyst 4 alone is in an activated state, vehicle 1 can adjust the oxygen storage amount of the upstream catalyst 4 to achieve the maximum exhaust gas purification performance at that time.

[0052] For example, vehicle 1 may change the target value Mut for the oxygen storage amount of the upstream catalyst 4 and the target value Mdt for the oxygen storage amount of the downstream catalyst 5 according to the operating conditions of vehicle 1.

[0053] For example, if the exhaust gas flow rate of vehicle 1 is less than a predetermined value, the target value Mdt of the oxygen storage amount of the downstream catalyst 5 may be shifted by a predetermined amount toward the downstream second predetermined value Md2, rather than the median of the range defined by the downstream first predetermined value Md1 and the downstream second predetermined value Md2. Alternatively, the target value Mdt of the oxygen storage amount of vehicle 1 may be shifted by a predetermined amount toward the downstream second predetermined value Md2, rather than the median of the range defined by the downstream first predetermined value Md1 and the downstream second predetermined value Md2, as the exhaust gas flow rate of vehicle 1 becomes less than a predetermined value. In these cases, the shifted target value Mdt of the oxygen storage amount of the downstream catalyst 5 shall be within the range defined by the downstream first predetermined value Md1 and the downstream second predetermined value Md2.

[0054] When the exhaust gas flow rate is low, the downstream catalyst 5 has a margin of exhaust gas purification capacity. In other words, when the exhaust gas flow rate is low, vehicle 1 does not need to adjust the oxygen storage amount of the downstream catalyst 5 to the median value (e.g., target value Mdt) of the range defined by the downstream first predetermined value Md1 and the downstream second predetermined value Md2, even if it worsens fuel efficiency.

[0055] As a result, vehicle 1 can shorten the operating time during which the controlled air-fuel ratio is set to the first air-fuel ratio after the fuel cut-off period ends. Therefore, vehicle 1 can ensure the exhaust gas purification performance of the downstream catalyst 5 while suppressing deterioration in fuel efficiency.

[0056] For example, if the exhaust gas flow rate of vehicle 1 is less than a predetermined value, the target value of the oxygen storage amount of the upstream catalyst 4 may be shifted by a predetermined amount toward the upstream first predetermined value Mu1, rather than the median value of the range defined by the upstream first predetermined value Mu1 and the upstream second predetermined value Mu2. Alternatively, the target value of the oxygen storage amount of vehicle 1 may be shifted by a predetermined amount toward the upstream first predetermined value Mu1, rather than the median value of the range defined by the upstream first predetermined value Mu1 and the upstream second predetermined value Mu2, as the exhaust gas flow rate of vehicle 1 becomes less than a predetermined value. In these cases, the shifted target value Mut of the oxygen storage amount of the upstream catalyst 4 shall be within the range defined by the upstream first predetermined value Mu1 and the upstream second predetermined value Mu2.

[0057] When the exhaust gas flow rate is low, the upstream catalyst 4 has a margin of exhaust purification capacity. In other words, when the exhaust gas flow rate is low, vehicle 1 does not need to adjust the target value of the oxygen storage amount of the upstream catalyst 4 to the median value of the range defined by the first upstream predetermined value Mu1 and the second upstream predetermined value Mu2, even at the expense of worsening fuel efficiency.

[0058] As a result, vehicle 1 can shorten the operating time during which the controlled air-fuel ratio is set to the second air-fuel ratio after the fuel cut-off period ends. Therefore, vehicle 1 can ensure the exhaust purification performance of the upstream catalyst 4 while suppressing deterioration in fuel efficiency.

[0059] For example, if the vehicle speed of vehicle 1 is lower than a predetermined speed, the target value of the oxygen storage amount of the downstream catalyst 5 may be shifted by a predetermined amount toward the downstream second predetermined value Md2, rather than the median of the range defined by the downstream first predetermined value Md1 and the downstream second predetermined value Md2. Alternatively, as the vehicle speed of vehicle 1 decreases below a predetermined speed, the target value of the oxygen storage amount of the downstream catalyst 5 may be shifted significantly toward the downstream second predetermined value Md2, rather than the median of the range defined by the downstream first predetermined value Md1 and the downstream second predetermined value Md2. In these cases, the shifted target value Mut of the oxygen storage amount of the upstream catalyst 4 is always within the range defined by the upstream first predetermined value Mu1 and the upstream second predetermined value Mu2, and the shifted target value Mdt of the oxygen storage amount of the downstream catalyst 5 is always within the range defined by the downstream first predetermined value Md1 and the downstream second predetermined value Md2.

[0060] At low vehicle speeds, the exhaust gas flow rate is small, and NOx can be purified (absorbed) by the upstream catalyst 4 alone. At low vehicle speeds, vehicle 1 does not need to adjust the target value of the oxygen storage amount of the downstream catalyst 5 to the median value of the range defined by the downstream first predetermined value Md1 and the downstream second predetermined value Md2, even if it worsens fuel efficiency.

[0061] As a result, vehicle 1 can ensure the exhaust purification performance of the downstream catalyst 5 while suppressing the deterioration of fuel efficiency.

[0062] For example, when vehicle 1 is accelerating rapidly, the target value of the oxygen storage amount in at least one of the upstream catalyst 4 and the downstream catalyst 5 may be set to a predetermined amount smaller than in cases other than rapid acceleration. Alternatively, when vehicle 1 is accelerating rapidly, the target value of the oxygen storage amount in at least one of the upstream catalyst 4 and the downstream catalyst 5 may be set to a smaller amount as the acceleration becomes more rapid compared to cases other than rapid acceleration. Rapid acceleration is defined as a case where the rate of change of vehicle speed is higher than a predetermined rate of change set in advance.

[0063] In scenes where vehicle 1 accelerates rapidly, the accelerator is pressed down, increasing the amount of air and thus the exhaust gas flow rate. As a result, the NOx purification rate tends to be low, so the target values ​​for the oxygen storage capacity of the upstream catalyst 4 and the downstream catalyst 5 are set to the values ​​on the upstream first predetermined value Mu1 side or the downstream first predetermined value Md1 side, respectively, rather than the median value.

[0064] As a result, vehicle 1 can suppress the deterioration of exhaust performance even during rapid acceleration.

[0065] For example, if the temperature of the upstream catalyst 4 is lower than a predetermined temperature (e.g., a temperature higher than the activation temperature), the amount by which the second air-fuel ratio changes from the stoichiometric air-fuel ratio to the lean side when adjusting the oxygen storage amount of the upstream catalyst 4 may be reduced. Alternatively, the lower the temperature of the upstream catalyst 4 is below a predetermined temperature (e.g., a temperature higher than the activation temperature), the smaller the amount by which the second air-fuel ratio changes from the stoichiometric air-fuel ratio to the lean side when adjusting the oxygen storage amount of the upstream catalyst 4 may be reduced.

[0066] This prevents NOx, HC, and CO exceeding the exhaust purification performance of the upstream catalyst 4 from flowing into the downstream catalyst 5.

[0067] For example, if the temperature of the downstream catalyst 5 is lower than a predetermined temperature (e.g., a temperature higher than the activation temperature), the amount by which the first air-fuel ratio changes from the stoichiometric air-fuel ratio to the rich side when adjusting the oxygen storage amount of the downstream catalyst 5 may be reduced. Alternatively, the lower the temperature of the downstream catalyst 5 is (e.g., a temperature higher than the activation temperature), the smaller the amount by which the first air-fuel ratio changes from the stoichiometric air-fuel ratio to the rich side when adjusting the oxygen storage amount of the downstream catalyst 5 may be reduced.

[0068] This prevents NOx, HC, and CO exceeding the exhaust purification performance of the downstream catalyst 5 from flowing into the downstream catalyst 5.

[0069] The above-described embodiment relates to a vehicle control method and a vehicle control device. [Explanation of Symbols]

[0070] 1…Vehicle 2…Internal combustion engine 3… Exhaust passage 4…Upstream catalyst 5… Downstream catalyst 6…Air-fuel ratio sensor 7…Oxygen sensor 8…Airflow meter 9... Crank angle sensor 10…Accelerator position sensor 11…Vehicle speed sensor 12…First temperature sensor 13…Second temperature sensor 15…Control Unit

Claims

1. In a vehicle control method in which a first catalytic converter and a second catalytic converter for exhaust gas purification are arranged in series in the exhaust passage of an internal combustion engine, with the first catalytic converter upstream of the second catalytic converter, and when predetermined fuel cut conditions are met, the fuel supply to the internal combustion engine is stopped, and when predetermined fuel cut recovery conditions are met, the fuel supply to the internal combustion engine is resumed, A vehicle control method characterized by performing a fuel cut recovery control after the end of fuel cut, in which, when the above fuel cut recovery conditions are met and fuel supply to the internal combustion engine is resumed, the oxygen storage amount of the first catalyst and the oxygen storage amount of the second catalyst are set to predetermined target values, and the air-fuel ratio of the internal combustion engine is controlled so that the oxygen storage amounts of the first catalyst and the oxygen storage amount of the second catalyst are set to predetermined target values.

2. The vehicle control method according to claim 1, characterized in that the control after the completion of the fuel cut is performed by setting the target air-fuel ratio of the internal combustion engine to a predetermined first air-fuel ratio and the oxygen storage amount of the second catalyst to a predetermined target value, and then setting the target air-fuel ratio of the internal combustion engine to a predetermined second air-fuel ratio and the oxygen storage amount of the first catalyst to a predetermined target value.

3. The vehicle control method according to claim 2, characterized in that the target value of the oxygen storage amount of the first catalyst is within a first predetermined range that is greater than or equal to a predetermined first predetermined value on the upstream side and less than or equal to a predetermined second predetermined value on the upstream side.

4. The above upstream first predetermined value is a value greater than or equal to the minimum oxygen storage amount that can keep the conversion rate of CO and HC in the exhaust within a predetermined regulatory range. The vehicle control method according to claim 3, characterized in that the above-mentioned upstream second predetermined value is a value less than or equal to the maximum oxygen storage amount that can keep the NOx conversion rate in the exhaust within a predetermined regulatory range.

5. The vehicle control method according to claim 2, characterized in that the target value of the oxygen storage amount of the second catalyst is within a second predetermined range that is greater than or equal to a predetermined first downstream predetermined value and less than or equal to a predetermined second downstream predetermined value.

6. The first predetermined value on the downstream side is a value greater than or equal to the minimum oxygen storage amount that can keep the conversion rate of CO and HC in the exhaust within a predetermined regulatory range. The vehicle control method according to claim 5, characterized in that the downstream second predetermined value is a value less than or equal to the maximum oxygen storage amount that can keep the NOx conversion rate in the exhaust within a predetermined regulatory range.

7. The vehicle control method according to any one of claims 1 to 6, characterized in that the control after the completion of the fuel cut is performed when the temperatures of the first catalyst and the second catalyst are above a predetermined temperature set in advance.

8. The vehicle control method according to any one of claims 1 to 6, characterized in that, after the fuel cut-off is completed, if the first catalyst is in an activated state and the second catalyst is in an inactivated state, the air-fuel ratio of the internal combustion engine is controlled so that the oxygen storage amount of the first catalyst reaches a target value.

9. The vehicle control method according to claim 1 or 2, characterized in that the target value of the oxygen storage amount of the first catalyst and the target value of the oxygen storage amount of the second catalyst are changed according to the operating conditions.

10. The vehicle control method according to claim 5, characterized in that, when the exhaust gas flow rate is small, the target value of the oxygen storage amount of the second catalyst is shifted to a value on the downstream second predetermined value side, rather than the median value of the range defined by the downstream first predetermined value and the downstream second predetermined value.

11. The vehicle control method according to claim 3, characterized in that, when the exhaust gas flow rate is small, the target value of the oxygen storage amount of the first catalyst is shifted from the median value of the range defined by the upstream first predetermined value and the upstream second predetermined value towards the upstream first predetermined value.

12. The vehicle control method according to claim 5, characterized in that, when the vehicle speed is low, the target value of the oxygen storage amount of the second catalyst is set to a value that is shifted towards the second downstream predetermined value from the median value of the range defined by the first downstream predetermined value and the second downstream predetermined value.

13. The vehicle control method according to claim 2, characterized in that when the vehicle is accelerating rapidly, the target value of the oxygen storage amount of at least one of the first catalyst and the second catalyst is made smaller than in the case of acceleration other than rapid acceleration.

14. The vehicle control method according to claim 2, characterized in that, when the temperature of the first catalyst is low, the amount of change of the second air-fuel ratio from the stoichiometric air-fuel ratio when adjusting the oxygen storage amount of the first catalyst is reduced.

15. The vehicle control method according to claim 2, characterized in that, when the temperature of the second catalyst is low, the amount of change from the stoichiometric air-fuel ratio of the first air-fuel ratio when adjusting the oxygen storage amount of the second catalyst is reduced.

16. A first catalytic converter for exhaust gas purification is located in the exhaust passage of an internal combustion engine, A second catalyst for exhaust gas purification is positioned downstream of the first catalyst mentioned above, A vehicle control device having a control unit that stops the fuel supply to the internal combustion engine when predetermined fuel cut conditions are met, and resumes the fuel supply to the internal combustion engine when predetermined fuel cut recovery conditions are met, The first catalyst and the second catalyst are arranged in series in the exhaust passage. A vehicle control device characterized in that, when the fuel cut recovery conditions are met and fuel supply to the internal combustion engine is resumed, the control unit sets the oxygen storage amount of the first catalyst and the oxygen storage amount of the second catalyst to predetermined target values, and performs fuel cut recovery control to control the air-fuel ratio of the internal combustion engine so that the oxygen storage amounts of the first catalyst and the oxygen storage amount of the second catalyst are each at predetermined target values.

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