Control device for internal combustion engine

Abstract

To provide a control device for an internal combustion engine capable of estimating an oxygen storage possible amount of a catalyst while suppressing deterioration of emissions.SOLUTION: A control device is for an internal combustion engine in which a catalyst is provided in an exhaust passage. The control device for the internal combustion engine includes: a control section that executes rich control for controlling an air-fuel ratio in the internal combustion engine after fuel cut to a rich air-fuel ratio; a first estimation section that estimates an oxygen storage possible amount of the catalyst from start of the rich control until the air-fuel ratio of exhaust gas discharged from the catalyst becomes the rich air-fuel ratio; a second estimation section that estimates an oxygen storage amount of the catalyst during execution of the rich control; and a stop section that stops the rich control when the oxygen storage amount becomes less than a determination value that is smaller than the oxygen storage possible amount.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a control device for an internal combustion engine. [Background technology]

[0002] There is a technique for estimating the amount of oxygen that can be occluded by a catalyst provided in an exhaust passage of an internal combustion engine. Specifically, during rich control after a fuel cut, the amount of oxygen that can be occluded is estimated during the period from when rich control starts until the air-fuel ratio of the exhaust gas discharged from the catalyst becomes a rich air-fuel ratio (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-159048 Summary of the Invention [Problem to be solved by the invention]

[0004] If rich control after fuel cut is performed until the air-fuel ratio of the exhaust gas discharged from the catalyst indicates a rich air-fuel ratio, CO and NH3 may be discharged from the catalyst, which may worsen emissions.

[0005] Therefore, an object of the present invention is to provide a control device for an internal combustion engine that can estimate the amount of oxygen that can be stored in a catalyst while suppressing deterioration of emissions. [Means for solving the problem]

[0006] The above object can be achieved by a control device for an internal combustion engine having a catalyst provided in an exhaust passage, the control device comprising: a control unit that executes rich control to control the air-fuel ratio in the internal combustion engine after a fuel cut to a rich air-fuel ratio; a first estimation unit that estimates the amount of oxygen that can be stored in the catalyst from the start of the rich control to the time when the air-fuel ratio of the exhaust gas discharged from the catalyst becomes a rich air-fuel ratio; a second estimation unit that estimates the amount of oxygen stored in the catalyst while the rich control is being executed; and a stop unit that stops the rich control when the amount of oxygen stored becomes less than a judgment value that is smaller than the amount of oxygen that can be stored. Effect of the Invention

[0007] It is possible to provide a control device for an internal combustion engine that can estimate the amount of oxygen that can be stored in a catalyst while suppressing deterioration of emissions. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of an internal combustion engine. [Diagram 2] 1 is a flowchart illustrating an example of OSC estimation control. [Diagram 3] 4 is a flowchart illustrating an example of rich control continuation / stop determination control after fuel cut. [Figure 4] 4 is a timing chart illustrating an example of OSC estimation control and rich control continuation / stop determination control after fuel cut. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [General configuration of an internal combustion engine] FIG. 1 is a schematic diagram of an internal combustion engine 1. The internal combustion engine 1 is mounted on, for example, a vehicle, but is not limited thereto, and may be mounted on a vessel or the like other than a vehicle. The internal combustion engine 1 has an engine body 10, an intake passage 20, and an exhaust passage 30. The engine body 10 is a multi-cylinder engine having a plurality of cylinders, and a combustion chamber 11, a piston 12, an ignition plug 16, and the like are provided in each cylinder. In addition, a connecting rod 13 and a crankshaft 14 are arranged inside the engine body 10. The piston 12 is connected to the crankshaft 14 by the connecting rod 13. The engine body 10 is provided with a rotation speed sensor 15, and an in-cylinder injection valve 17 is provided for each cylinder. The rotation speed sensor 15 detects the rotation speed of the crankshaft 14 to detect the rotation speed of the engine body 10. The in-cylinder injection valve 17 directly injects fuel into the combustion chamber 11. Incidentally, a port injection valve that injects fuel toward an intake port of the engine body 10 may be provided instead of the in-cylinder injection valve 17, or a port injection valve may be provided in addition to the in-cylinder injection valve 17. The spark plug 16 ignites the air-fuel mixture in the combustion chamber 11. An intake passage 20 and an exhaust passage 30 are connected to the intake port and exhaust port of the engine body 10, respectively. An intake valve 18a and an exhaust valve 18b open and close the intake port and exhaust port of the engine body 10, respectively.

[0010] In the intake passage 20, an air cleaner 21, an air flow meter 22, and a throttle valve 23 are provided in this order from upstream to downstream. The air cleaner 21 removes dust and other particles from the air flowing in from the outside. The air flow meter 22 acquires the amount of intake air Ga. The throttle valve 23 is driven by, for example, an actuator (not shown) to adjust the amount of intake air Ga.

[0011] When intake valve 18a opens, air is introduced from intake passage 20 into combustion chamber 11. A mixture of air and fuel injected from in-cylinder injection valve 17 is compressed by piston 12 and ignited by spark plug 16. Ignition of the mixture causes piston 12 to reciprocate up and down within combustion chamber 11, rotating crankshaft 14. Exhaust gas after combustion is discharged from exhaust passage 30.

[0012] The exhaust passage 30 is provided with an upstream sensor 31a, a front catalyst 32a, a downstream sensor 31b, and a rear catalyst 32b in this order from upstream to downstream. The upstream sensor 31a and the downstream sensor 31b are air-fuel ratio sensors that detect the air-fuel ratio of the exhaust gas flowing through the exhaust passage 30, but are not limited thereto. At least one of these sensors may be an oxygen concentration sensor that can detect the air-fuel ratio of the exhaust gas by detecting the oxygen concentration of the exhaust gas. The upstream sensor 31a detects the air-fuel ratio of the exhaust gas discharged from the engine body 10 and flowing into the front catalyst 32a. The downstream sensor 31b detects the air-fuel ratio of the exhaust gas discharged from the front catalyst 32a and flowing into the rear catalyst 32b.

[0013] The front catalyst 32a and the rear catalyst 32b are three-way catalysts that contain catalytic metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) and have an oxygen storage capacity. The three-way catalyst has a catalytic action and an oxygen storage capacity, and thus has a purification action of NOx and HC according to the oxygen storage amount OSA.

[0014] An ECU (Electric Control Unit) 100 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a storage device such as a flash memory, and performs various controls by executing programs stored in the ROM or the storage device. The ECU 100 controls the spark plug 16, the in-cylinder injection valve 17, and the throttle valve 23 based on the amount of operation of the accelerator pedal or the brake pedal operated by the driver, the rotation speed and the load of the engine body 10, etc. The ECU 100 receives inputs of the rotation speed detected by the rotation speed sensor 15, the intake air amount detected by the air flow meter 22, and the detected air-fuel ratios AFup and AFdown detected by the upstream sensor 31a and the downstream sensor 31b, respectively.

[0015] The ECU 100 feedback controls the amount of fuel injected from the in-cylinder injection valve 17 and the opening of the throttle valve 23 based on the detected air-fuel ratio AFup of the upstream sensor 31a so that the detected air-fuel ratio of the upstream sensor 31a becomes the target air-fuel ratio AFT. As a result, the air-fuel ratio of the exhaust gas discharged from the engine body 10 is controlled to the target air-fuel ratio AFT. The ECU 100 sets the target air-fuel ratio AFT at the time of recovery from a fuel cut to a rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio ST. This is to prevent the front catalyst 32a from being unable to sufficiently purify NOx at the time of recovery, since the oxygen storage amount OSA has increased due to exposure to a lean atmosphere during the fuel cut.

[0016] The ECU 100 is an example of a control device for an internal combustion engine. The ECU 100 also functionally realizes a control unit, a first estimation unit, a second estimation unit, and a stopping unit, which will be described later, by the above-mentioned CPU, RAM, ROM, storage device, etc.

[0017] [OSC Estimation Control] The ECU 100 executes control to estimate the oxygen storable amount OSC of the front catalyst 32a. FIG. 2 is a flowchart illustrating the OSC estimation control. The ECU 100 determines whether or not the estimation of the oxygen storable amount OSC is incomplete (step S1). If the answer is No in step S1, that is, if the estimation of the oxygen storable amount OSC has already been completed, this control ends. If the answer is Yes in step S1, that is, if the estimation of the oxygen storable amount OSC has not been completed, the ECU 100 determines whether or not a prerequisite for the estimation is satisfied (step S2). The prerequisite includes, for example, that warm-up control is not being executed. If the answer is No in step S2, this control ends.

[0018] If the answer is Yes in step S2, the ECU 100 determines whether or not the oxygen storable amount OSC is being estimated (step S3). Specifically, this determination is made based on whether or not an OSC estimation flag is on. If the answer is No in step S3, the ECU 100 determines whether or not the internal combustion engine 1 has returned from a fuel cut (step S4). If the answer is No in step S4, this control ends.

[0019] If the answer is Yes in step S4, the ECU 100 estimates the oxygen storage amount OSA of the front catalyst 32a (step S5). The oxygen storage amount OSA is estimated during rich control when returning from fuel cut. The oxygen storage amount OSA decreases over time because oxygen stored in the front catalyst 32a during fuel cut is consumed by rich control when returning from fuel cut. The oxygen storage amount OSA is estimated based on the intake air amount Ga and the detected air-fuel ratio AFup. The fuel injection amount Q may be used instead of the intake air amount Ga. For example, the oxygen storage amount OSA may be estimated by the method described in JP 2009-19558 A, or may be estimated by other known methods. Step S5 is a process executed by the second estimation unit. Next, the ECU 100 turns on the OSC estimation flag (step S6).

[0020] If the answer is Yes in step S3, the ECU 100 judges whether or not the detected air-fuel ratio AFdown of the downstream sensor 31b indicates a rich air-fuel ratio (step S7). If the answer is No in step S7, this control ends. If the answer is Yes in step S7, the ECU 100 estimates the oxygen storable amount OSC (step S8). Specifically, the difference between the oxygen storage amount OSA before the start of the rich control after fuel cut and the oxygen storage amount OSA when the detected air-fuel ratio AFdown indicates a rich air-fuel ratio is estimated as the oxygen storable amount OSC. Step S8 is an example of a process executed by the first estimation unit. Next, the ECU 100 turns off the OSC estimation flag (step S9) and counts up the number of estimations (step S10).

[0021] Next, the ECU 100 calculates the average value of the estimated value of the oxygen storable amount OSC (step S11). Next, the ECU 100 determines whether the number of estimations is equal to or greater than the upper limit number (step S12). The upper limit number is, for example, three times. If the answer is No in step S12, the control ends. If the answer is Yes in step S12, the ECU 100 updates the learned value of the oxygen storable amount OSC to the above-mentioned average value (step S13). Next, the ECU 100 turns on the OSC estimation completion flag (step S14).

[0022] [Rich control continues after fuel cut / stop judgment control] 3 is a flowchart illustrating the rich control continuation / stop determination control after fuel cut. This control is repeatedly executed while the internal combustion engine 1 is operating. The rich control continuation / stop determination control after fuel cut is executed in parallel with the OSC estimation control. The ECU 100 determines whether or not the rich control is being executed after recovery from a fuel cut (step S21). If the answer is No in step S21, this control ends.

[0023] If the answer is Yes in step S21, the ECU 100 determines whether or not the estimation of the oxygen storable amount OSC is incomplete based on the above-mentioned OSC estimation flag (step S22). If the answer is Yes in step S22, the ECU 100 determines whether or not the detected air-fuel ratio AFdown of the downstream sensor 31b is a rich air-fuel ratio (step S23). If the answer is No in step S23, the ECU 100 continues the rich control (step S24). That is, the rich control is continued until the detected air-fuel ratio AFdown becomes rich while the estimation is incomplete. If the answer is Yes in step S23, the ECU 100 stops the rich control (step S25). That is, the rich control is stopped at the point when the detected air-fuel ratio AFdown becomes rich while the estimation is incomplete.

[0024] If the answer is No in step S22, the ECU 100 judges whether the oxygen storage amount OSA is less than a judgment value (step S26). The judgment value is set to a value smaller than the oxygen storage capacity OSC. If the answer is No in step S26, the ECU 100 continues the rich control (step S27). This allows the estimation of the oxygen storage amount OSA of the front catalyst 32a to continue. If the answer is Yes in step S26, the ECU 100 stops the rich control (step S25). This allows the rich control to be stopped before the air-fuel ratio of the exhaust gas discharged from the front catalyst 32a becomes a rich air-fuel ratio. This makes it possible to estimate the oxygen storage capacity OSC of the front catalyst 32a while suppressing deterioration of emissions. Steps S25 and S26 are an example of processing executed by a stop unit.

[0025] Fig. 4 is a timing chart showing an example of the OSC estimation control and the rich control continuation / stop determination control after fuel cut. Fig. 4 shows the fuel cut state, the detected air-fuel ratio AFdown, the amount of NH3 discharged, the number of times of estimating the oxygen storable amount OSC, the OSC estimation completion flag, the estimated value of the oxygen storable amount OSC, the average value, and the learned value. The estimated value is shown by a dashed line, the average value is shown by a solid line, and the learned value is shown by a dashed line.

[0026] When fuel cut is performed (time t1), the detected air-fuel ratio AFdown indicates lean, and when fuel cut ends (time t2), rich control is performed and the detected air-fuel ratio AFdown indicates approximately the stoichiometric air-fuel ratio ST. When the detected air-fuel ratio AFdown indicates a rich air-fuel ratio during rich control, the oxygen storable amount OSC is estimated, the rich control is stopped, and the number of times that the oxygen storable amount OSC has been estimated is counted (time t3). Thereafter, the oxygen storable amount OSC is estimated in the same manner, the rich control is stopped, the number of times that the oxygen storable amount OSC has been estimated is counted, and an average value is calculated based on the previous value and the current value of the oxygen storable amount OSC (time t4). When the number of times that the oxygen storable amount OSC has been estimated is the third, the learned value is updated to the average value (time t5).

[0027] The rich control when the fuel cut is resumed is stopped when the oxygen storage amount OSA becomes less than the judgment value (time t6). As described above, the judgment value is smaller than the oxygen storage capacity OSC, so the oxygen storage amount OSA becomes less than the judgment value before the detected air-fuel ratio AFdown indicates a rich air-fuel ratio, and the rich control is stopped. In this way, the rich control is stopped before the detected air-fuel ratio AFdown indicates a rich air-fuel ratio, so the oxygen storage capacity OSC can be estimated while suppressing deterioration of emissions.

[0028] Although a preferred embodiment of the present invention has been described in detail above, the present invention is not limited to such a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0029] 1. Internal combustion engine 10. Main Body of the Agency 30 Exhaust passage 31b Downstream sensor 32a Front stage catalyst 100 ECU (control device for internal combustion engine, control unit, first estimation unit, second estimation unit, stop unit)

Claims

[Claim 1] A control device for an internal combustion engine having a catalyst provided in an exhaust passage, a control unit that executes a rich control to control an air-fuel ratio in the internal combustion engine after a fuel cut to a rich air-fuel ratio; a first estimation unit that estimates an amount of oxygen that can be occluded by the catalyst from when the rich control is started until an air-fuel ratio of exhaust gas discharged from the catalyst becomes a rich air-fuel ratio; a second estimation unit that estimates an oxygen storage amount of the catalyst while the rich control is being executed; a stop unit that stops the rich control when the oxygen storage amount becomes less than a determination value that is smaller than the oxygen storable amount.

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