Engine control device

Abstract

To provide an engine control device ensuring effective frequency of an abnormality diagnosis of an exhaust sensor.SOLUTION: An engine control device includes: a catalyst purifying exhaust air; and an exhaust air sensor detecting a status value related to an air fuel ratio of the exhaust air. The engine control device is provided with: a calculation part calculating a target air fuel ratio of the engine on the basis of a demand value to the engine; a compensation part compensating the target air fuel ratio on the basis of the detected value of the exhaust air sensor; a control part controlling the engine on the basis of the target air fuel ratio after compensation; an estimation part estimating a temperature of the catalyst on the basis of the target air fuel ratio before compensation; and a diagnosis part executing the abnormality diagnosis of the exhaust air sensor on the condition that the temperature of the catalyst is an activation temperature or higher.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an engine control device. [Background technology]

[0002] There is a technique for estimating the catalyst temperature based on the air-fuel ratio of the exhaust gas detected by an exhaust sensor (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-125478 Summary of the Invention [Problem to be solved by the invention]

[0004] If an abnormality occurs in the exhaust sensor, the accuracy of the exhaust sensor's detection of the exhaust air-fuel ratio decreases, and the accuracy of estimating the catalyst temperature also decreases. Therefore, in such a case, it is possible to estimate the catalyst temperature based on the engine's target air-fuel ratio. However, the engine's target air-fuel ratio is corrected based on the air-fuel ratio detected by the exhaust sensor, and the engine is controlled based on the corrected target air-fuel ratio. If the catalyst temperature is estimated based on such a corrected target air-fuel ratio, the accuracy of estimating the catalyst temperature may decrease.

[0005] In this case, an abnormality diagnosis may be performed to determine whether the exhaust sensor is abnormal. The condition for performing the exhaust sensor abnormality diagnosis is that the catalyst temperature is equal to or higher than the activation temperature, in order to prevent a decrease in exhaust emissions. As described above, if an abnormality occurs in the exhaust sensor, the accuracy of estimating the catalyst temperature decreases. As a result, the estimated catalyst temperature may not be equal to or higher than the activation temperature, and the effective frequency of performing the exhaust sensor abnormality diagnosis may decrease.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an engine control device that ensures an effective frequency of abnormality diagnosis of an exhaust sensor. [Means for solving the problem]

[0007] The above object can be achieved by an engine control device equipped with a catalyst for purifying exhaust gas and an exhaust sensor for detecting a state value related to the air-fuel ratio of the exhaust gas, the engine control device comprising: a calculation unit that calculates a target air-fuel ratio for the engine based on the operating state of the engine; a correction unit that corrects the target air-fuel ratio based on the detection value of the exhaust sensor; a control unit that controls the engine based on the corrected target air-fuel ratio; an estimation unit that estimates the temperature of the catalyst based on the target air-fuel ratio before correction; and a diagnosis unit that performs an abnormality diagnosis of the exhaust sensor on the condition that the temperature of the catalyst is equal to or higher than an activation temperature. [Effects of the Invention]

[0008] It is possible to provide an engine control device that ensures an effective frequency of abnormality diagnosis of the exhaust sensor. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of an engine. [Figure 2] 3 is a flowchart illustrating a control executed by an ECU. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Engine outline] FIG. 1 is a schematic diagram of an engine 10. The engine 10 is mounted on, for example, a vehicle and functions as a power source for driving the vehicle. The engine 10 has an engine body 11, an intake passage 20, and an exhaust passage 24. The engine body 11 is, for example, a multi-cylinder engine having multiple cylinders. The engine body 11 is provided with an in-cylinder injection valve 12 and a spark plug 14. The in-cylinder injection valve 12 directly injects fuel into the combustion chamber of the engine 10. Note that a port injection valve may be provided instead of or in addition to the in-cylinder injection valve 12. The spark plug 14 ignites a mixture of fuel and air.

[0011] A throttle valve 22 is provided in the intake passage 20. The throttle valve 22 is driven, for example, by an actuator (not shown) to adjust the amount of intake air. An air flow meter 21 is provided in the intake passage 20 upstream of the throttle valve 22. The air flow meter 21 detects the amount of intake air.

[0012] A first catalyst 26 and a second catalyst 28 are provided in the exhaust passage 24, downstream of the first catalyst 26. The first catalyst 26 and the second catalyst 28 are three-way catalysts that contain catalytic metals of platinum (Pt), palladium (Pd), and rhodium (Rh), respectively, and have oxygen storage capacity. The three-way catalyst has catalytic action and oxygen storage capacity, and therefore has the effect of purifying NOx and HC according to the amount of oxygen stored.

[0013] An exhaust sensor 25 is provided in the exhaust passage 24 upstream of the first catalyst 26, and an exhaust sensor 27 is provided upstream of the second catalyst 28 and downstream of the first catalyst 26. An air-fuel ratio sensor or an oxygen concentration sensor can be used as the exhaust sensors 25 and 27. The air-fuel ratio sensor outputs a linear signal corresponding to the air-fuel ratio of the exhaust gas and detects the air-fuel ratio (A / F) as a status value. The oxygen concentration sensor outputs a signal corresponding to the oxygen concentration in the gas and detects the oxygen concentration as a status value. The exhaust sensors 25 and 27 are connected to the ECU 100.

[0014] The ECU 100 is an electronic control unit that includes a processing circuit for performing various calculations related to vehicle driving control and a memory that stores control programs and data. The ECU 100 is an example of an engine control device, and functionally realizes a calculation unit, a correction unit, a control unit, an estimation unit, and a diagnosis unit, which will be described in detail later. The ECU 100 is electrically connected to the direct injection valve 12, the spark plug 14, the air flow meter 21, the throttle valve 22, and the exhaust sensors 25 and 27.

[0015] [Engine control and abnormality diagnosis control] 2 is a flowchart illustrating engine control and abnormality diagnosis control executed by ECU 100. Note that the abnormality diagnosis control will be described by taking an example of diagnosing whether or not the exhaust sensor 25 is abnormal. ECU 100 calculates a target air-fuel ratio based on the operating state of engine 10 (step S1). The operating state of engine 10 includes the engine speed and engine load factor. Next, ECU 100 corrects the calculated target air-fuel ratio based on the detection value of exhaust sensor 25 (step S2). For example, if the air-fuel ratio detected by exhaust sensor 25 is richer than the target air-fuel ratio, the target air-fuel ratio is corrected to be leaner, and if the detected air-fuel ratio is leaner than the target air-fuel ratio, the target air-fuel ratio is corrected to be richer.

[0016] Next, the ECU 100 controls the engine 10 based on the corrected target air-fuel ratio (step S3). For example, the amount of fuel injected from the in-cylinder injection valve 12 is feedback-controlled so that the actual air-fuel ratio of the exhaust gas matches the corrected target air-fuel ratio. This allows the actual air-fuel ratio of the exhaust gas to be controlled with high precision, preventing deterioration of exhaust emissions and fuel economy.

[0017] Next, the ECU 100 estimates the temperature of the first catalyst 26 based on the target air-fuel ratio before correction (step S4). For example, the temperature of the first catalyst 26 is estimated as follows: The exhaust gas temperature is calculated based on the engine speed, the engine load factor, and the target air-fuel ratio before correction. Next, the exhaust gas flow rate is calculated based on the intake air amount and the fuel injection amount. The temperature of the exhaust gas flowing into the first catalyst 26 is calculated based on the exhaust gas temperature, the exhaust gas flow rate, and the amount of heat removed from the exhaust gas before it flows into the first catalyst 26. The amount of heat removed from the exhaust gas before it flows into the first catalyst 26 is, for example, the amount of heat removed by the exhaust passage 24 or the turbocharger turbine. This amount of heat is obtained in advance through experiments. Next, the heat of an oxidation-reduction reaction in the first catalyst 26 is calculated based on the target air-fuel ratio before correction. For example, if the target air-fuel ratio before correction is a rich air-fuel ratio, heat of a reduction reaction is generated in the first catalyst 26. If the target air-fuel ratio before correction is a lean air-fuel ratio, heat of an oxidation reaction is generated in the first catalyst 26. These reaction heats are obtained in advance through experiments. Next, the temperature of the first catalyst 26 is calculated based on the temperature of the exhaust gas flowing into the first catalyst 26 and the heat of the oxidation-reduction reaction in the first catalyst 26. Note that the method for estimating the temperature of the first catalyst 26 is not limited to the above example, and other known methods may be used.

[0018] Next, the ECU 100 determines whether or not the estimated temperature of the first catalyst 26 is equal to or higher than the activation temperature, which is one of the conditions for executing the abnormality diagnosis of the exhaust sensor 25 (step S5). This execution condition is established to suppress deterioration of exhaust emissions due to the execution of the abnormality diagnosis. If the determination in step S5 is No, this control ends.

[0019] If the answer is Yes in step S5, the ECU 100 determines whether or not other conditions for performing abnormality diagnosis are met (step S6). The conditions for performing other abnormality diagnosis include, for example, that the engine speed, engine load, and engine coolant temperature are within predetermined ranges, that the engine 10 is not in an idling state, etc. If the answer is No in step S6, this control ends.

[0020] If the answer in step S6 is Yes, the ECU 100 executes an abnormality diagnosis of the exhaust sensor 25 (step S7). The abnormality diagnosis is performed by, for example, increasing or decreasing the fuel injection amount to increase or decrease the air-fuel ratio of the exhaust. At this time, based on the amount of change in the detection value of the exhaust sensor 25, it is diagnosed whether or not the exhaust sensor 25 is abnormal.

[0021] As described above, the temperature of the first catalyst 26 is estimated based on the pre-correction target air-fuel ratio, not the post-correction target air-fuel ratio. Therefore, even if an abnormality occurs in the exhaust sensor 25, a decrease in the accuracy of estimating the temperature of the first catalyst 26 is suppressed. This ensures that the frequency of performing abnormality diagnosis of the exhaust sensor 25 is maintained.

[0022] In the above embodiment, an example has been described in which an abnormality diagnosis is performed on the exhaust sensor 25, but the same may be performed when an abnormality diagnosis is performed on the exhaust sensor 27. When an abnormality diagnosis is performed on the exhaust sensor 27, a condition is that the temperature of the second catalyst 28 estimated based on the uncorrected target air-fuel ratio is equal to or higher than the activation temperature.

[0023] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0024] 10 Engine 11 Engine body 25 Exhaust sensor 26 First catalyst 100 ECU (controller, calculation unit, correction unit, control unit, estimation unit, diagnosis unit)

Claims

[Claim 1] 1. A control device for an engine equipped with a catalyst for purifying exhaust gas and an exhaust sensor for detecting a state value related to an air-fuel ratio of the exhaust gas, a calculation unit that calculates a target air-fuel ratio of the engine based on an operating state of the engine; a correction unit that corrects the target air-fuel ratio based on a detection value of the exhaust sensor; a control unit that controls the engine based on the corrected target air-fuel ratio; an estimation unit that estimates a temperature of the catalyst based on the target air-fuel ratio before correction; a diagnosis unit that executes an abnormality diagnosis for the exhaust sensor on the condition that the temperature of the catalyst is equal to or higher than an activation temperature.

Images