JP2023002072A - Engine control device - Google Patents

Abstract

To solve a problem that abnormal diagnosis of an air-fuel ratio sensor becomes hard to be executed in a state that a catalyst temperature is low.SOLUTION: An engine control device 10 calculates a first catalyst temperature by using a measurement value of an air-fuel ratio by a front air-fuel ratio sensor 26 and calculates a second catalyst temperature by using a calculation value of the air-fuel ratio calculated from amounts of intake air and a fuel supplied for combustion in a combustion chamber 12. The engine control device 10 determines presence or absence of establishment of execution conditions of abnormality diagnosis of the front air-fuel ratio sensor 26 by using the second catalyst temperature of them.SELECTED DRAWING: Figure 1

Description

The present invention relates to an engine control device that diagnoses an abnormality of an air-fuel ratio sensor installed in an exhaust passage.

As an engine control device for diagnosing an air-fuel ratio sensor as described above, a device described in Patent Document 1 is known. The engine control device of this document is applied to an engine in which a catalytic device for purifying exhaust gas is installed in a portion of the exhaust passage downstream of an air-fuel ratio sensor to be diagnosed. The engine control device performs abnormality diagnosis of the air-fuel ratio sensor while switching the air-fuel ratio of the air-fuel mixture combusted in the combustion chamber between a rich air-fuel ratio and a lean air-fuel ratio. The rich air-fuel ratio indicates an air-fuel ratio that is richer than the stoichiometric air-fuel ratio, and the lean air-fuel ratio indicates an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. Incidentally, in the same engine control system, the abnormality diagnosis of the air-fuel ratio sensor is performed on the condition that the catalyst temperature of the catalyst device is equal to or higher than a certain temperature.

Japanese Unexamined Patent Application Publication No. 2018-3606

During combustion at the rich air-fuel ratio/lean air-fuel ratio, the temperature of the exhaust gas is lower than that during combustion at the stoichiometric air-fuel ratio, and as a result, the catalyst temperature is also lowered. Thus, the air-fuel ratio is one of the factors that affect the catalyst temperature. Therefore, by adding the air-fuel ratio to the parameters used for estimation, the estimation accuracy of the catalyst temperature can be improved.

Here, it is considered to use the catalyst temperature estimated using the air-fuel ratio measured value by the air-fuel ratio sensor to determine whether or not the conditions for executing the abnormality diagnosis of the air-fuel ratio sensor are met. At this time, the air-fuel ratio sensor is in a state in which abnormality diagnosis has not been completed, and may not function normally. On the other hand, if the measured value of the air-fuel ratio sensor with an abnormality is used, the catalyst temperature may not be properly estimated. Therefore, if the measured value of the air-fuel ratio sensor is used to estimate the catalyst temperature and the estimated value of the catalyst temperature is used to determine whether to perform the abnormality diagnosis, the abnormality diagnosis of the air-fuel ratio sensor will be performed under inappropriate conditions. There is a risk of being

An engine control device for solving the above problems diagnoses an abnormality of an air-fuel ratio sensor in an engine in which an air-fuel ratio sensor and a catalytic device for purifying exhaust gas are installed in an exhaust passage through which exhaust gas generated by combustion of an air-fuel mixture in a combustion chamber flows. to implement. Further, the same engine control device includes, as processing for estimating the catalyst temperature of the catalyst device of the catalyst device, a first estimation processing for estimating the catalyst temperature using an air-fuel ratio measurement value obtained by an air-fuel ratio sensor; and a second estimation process of estimating the catalyst temperature using an air-fuel ratio calculated from the respective amounts of intake air and fuel used for combustion. In the engine control system, the execution condition of the abnormality diagnosis includes that the estimated value of the catalyst temperature obtained by the second estimation process is equal to or higher than a predetermined diagnosis lower limit temperature.

In both the first estimation process and the second estimation process performed by the engine control device, it is possible to estimate the catalyst temperature reflecting the influence of the air-fuel ratio. Of these, the second estimation process does not use the measured value of the air-fuel ratio sensor, so even when the air-fuel ratio sensor is abnormal, an inappropriate value that deviates greatly from the actual value will not occur. Therefore, if the catalyst temperature estimated in the second estimating process is used to determine whether the execution conditions for abnormality diagnosis are satisfied, it becomes difficult to perform abnormality diagnosis in an inappropriate state even if there is an abnormality in the air-fuel ratio sensor.

1 is a diagram schematically showing the configuration of an embodiment of an engine control device; FIG. FIG. 3 is a control block diagram showing the flow of processing relating to estimation of a first catalyst temperature THC1 in a first estimation processing performed by the engine control device; FIG. 5 is a control block diagram showing the flow of processing relating to estimation of a second catalyst temperature THC2 in a second estimation processing performed by the engine control device;

An embodiment of the engine control device will be described in detail below with reference to FIGS. 1 to 3. FIG.
<Configuration of Engine 11>
First, referring to FIG. 1, the configuration of an engine 11 to which an engine control device 10 of this embodiment is applied will be described. Note that the engine 11 is mounted on the vehicle. The engine 11 has a combustion chamber 12 in which an air-fuel mixture is combusted. The engine 11 also includes an intake passage 13 that is a passage for introducing intake air into the combustion chamber 12 and an exhaust passage 14 that is a passage for exhaust from the combustion chamber 12 . The intake passage 13 is provided with a throttle valve 15 that is a flow control valve for intake air. An injector 16 for injecting fuel into intake air is installed in a portion of the intake passage 13 downstream of the throttle valve 15 . An ignition device 17 that ignites the air-fuel mixture by spark discharge is installed in the combustion chamber 12 into which the air-fuel mixture, that is, the air-fuel mixture is introduced through the intake passage 13 . On the other hand, the exhaust passage 14 is provided with a catalyst device 18 for purifying exhaust gas. A filter device 19 for collecting particulate matter in exhaust gas is installed in a portion of the exhaust passage 14 downstream of the catalyst device 18 . The catalyst device 18 and the filter device 19 carry a three-way catalyst that simultaneously oxidizes HC and CO and reduces NOx in the exhaust gas. The catalyst device 18 and the filter device 19 also carry an oxygen storage agent as a co-catalyst for enhancing the catalytic action of the three-way catalyst.

<Configuration of engine control device 10>
Next, the configuration of the engine control device 10 that controls the engine 11 will be described. The engine control device 10 is configured as an electronic control unit including an arithmetic processing device 20 and a storage device 21 . The arithmetic processing device 20 is a device that executes arithmetic processing for engine control. The storage device 21 is a device that stores programs and data for engine control.

Various sensors are connected to the engine control device 10 to detect state quantities indicating the operating state of the engine 11 . Such sensors include an air flow meter 22 , a throttle opening sensor 23 , an intake pressure sensor 24 , a crank angle sensor 25 , a front air-fuel ratio sensor 26 and a rear air-fuel ratio sensor 27 . Furthermore, an accelerator pedal sensor 28, a vehicle speed sensor 29, an outside air temperature sensor 30, and a water temperature sensor 31 are also included in the above sensors. The airflow meter 22 is a sensor that detects the intake flow rate GA of the intake passage 13 . The intake pressure sensor 24 is a sensor that detects an intake pressure PM, which is the pressure of intake air in a portion of the intake passage 13 downstream of the throttle valve 15 . The throttle opening sensor 23 is a sensor that detects the throttle opening TA, which is the opening of the throttle valve 15 . The crank angle sensor 25 is a sensor that detects a crank angle θ that is the rotation angle of the crankshaft that is the output shaft of the engine 11 . The front air-fuel ratio sensor 26 is a sensor that detects the air-fuel ratio of the exhaust flowing into the catalyst device 18 . The rear air-fuel ratio sensor 27 is a sensor that detects the air-fuel ratio of exhaust gas flowing out from the catalyst device 18 . The accelerator pedal sensor 28 is a sensor that detects the accelerator pedal opening ACC, which is the amount of operation of the accelerator pedal by the driver. The vehicle speed sensor 29 is a sensor that detects the running speed V of the vehicle. The outside air temperature sensor 30 is a sensor that detects the outside air temperature THA, which is the temperature of the air outside the vehicle. The water temperature sensor 31 is a sensor that detects an engine water temperature THW, which is the temperature of engine cooling water. Note that the engine control device 10 obtains the engine speed NE from the detection result of the crank angle θ by the crank angle sensor 25 . The engine control device 10 also obtains the engine load factor KL from the intake air flow rate GA, the throttle opening TA, the engine speed NE, and the like. The engine load factor KL represents the filling rate of intake air in the combustion chamber 12 .

The engine control device 10 determines each operation amount of the engine 11 according to the operating state of the engine 11 ascertained from the detection results of these sensors. The operation amount of the engine 11 determined by the engine control device 10 includes the throttle opening TA, the fuel injection amount Q of the injector 16, and the ignition timing SA of the air-fuel mixture by the ignition device 17. FIG. Then, the engine control device 10 controls the engine by driving the throttle valve 15, the injector 16, the ignition device 17, etc. according to the determined operation amount. The engine control device 10 performs air-fuel ratio feedback control as part of engine control. In the air-fuel ratio feedback control, the engine control device 10 feedback-adjusts the fuel injection amount Q of the injector 16 so that the output λf of the front air-fuel ratio sensor 26 approaches the value indicating the stoichiometric air-fuel ratio.

<Diagnosis of abnormality of front air-fuel ratio sensor 26>
The engine control device 10 performs abnormality diagnosis of the front air-fuel ratio sensor 26 as part of engine control. During this abnormality diagnosis, the engine control device 10 changes the air-fuel ratio of the air-fuel mixture combusted in the combustion chamber 12 from the stoichiometric air-fuel ratio to a rich air-fuel ratio or a lean air-fuel ratio. The rich air-fuel ratio indicates an air-fuel ratio that is richer than the stoichiometric air-fuel ratio, and the lean air-fuel ratio indicates an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. Then, the engine control device 10 performs abnormality diagnosis based on changes in the output λf of the front air-fuel ratio sensor 26 with respect to changes in the air-fuel ratio.

The engine control device 10 executes such an abnormality diagnosis of the front air-fuel ratio sensor 26 in response to establishment of a predetermined execution condition. An execution condition is met when all of a plurality of preset requirements are satisfied. Requirements for establishment of such execution conditions include the following requirements (a) to (d). Requirement (a) is that the abnormality diagnosis of the catalyst device 18 has not been completed in the current trip. Requirement (b) is that the engine 11 has been warmed up. Requirement (c) is that the operating conditions of the engine 11 are stable, that is, that the change in the engine speed NE and the engine load factor KL is small. Requirement (d) is that the catalyst temperature of the catalyst device 18 is equal to or higher than a predetermined diagnostic lower limit temperature. The diagnosis lower limit temperature is set to a temperature higher than the lower limit of the catalyst temperature range at which the catalyst supported by the catalyst device 18 and the oxygen storage agent are sufficiently activated.

<Estimation of catalyst temperature>
Next, the details of the catalyst temperature estimation process performed by the engine control device 10 will be described. The engine control device 10 obtains two temperatures, the first catalyst temperature THC1 and the second catalyst temperature THC2, as estimated values of the catalyst temperature. The first catalyst temperature THC1 is the catalyst temperature estimated using the air-fuel ratio detected by the front air-fuel ratio sensor 26 . On the other hand, the second catalyst temperature THC2 is the catalyst temperature estimated using the air-fuel ratio calculated from the respective amounts of intake air and fuel used for combustion in the combustion chamber 12 .

FIG. 2 shows the processing flow of the engine control device 10 for estimating the first catalyst temperature THC1. FIG. 3 shows the processing flow of the engine control device 10 for estimating the second catalyst temperature THC2. As shown in FIGS. 2 and 3, both the first catalyst temperature THC1 and the second catalyst temperature THC2 are determined by the engine exit gas temperature estimation process P1, the exhaust flow rate calculation process P2, the catalyst entrance gas temperature estimation process P3, and the catalyst temperature estimation process P3. It is estimated through four processes of the temperature estimation process P4.

In the engine output gas temperature estimation process P1, the engine control device 10 first calculates a steady engine output gas temperature T1 based on the engine speed NE and the engine load factor KL. The steady engine exhaust gas temperature T1 is the temperature of the exhaust discharged from the combustion chamber 12 to the exhaust passage 14 when the engine 11 is in steady operation under the current engine speed NE and engine load factor KL. represents the temperature. Steady operation here refers to an operating state that meets all of the following states (i) to (ni). State (i) is a state in which warming up of the engine 11 is completed. In the state (b), the outside air temperature THA is the standard temperature. The state (ha) is a state in which retardation control of the ignition timing SA is not performed in order to promote warm-up of the catalyst device 18 or the like. The (in) state is a state in which the air-fuel ratio of the air-fuel mixture burning in the combustion chamber 12 is the stoichiometric air-fuel ratio. The engine control device 10 uses a calculation map M1 stored in advance in the storage device 21 to calculate the steady-state engine output gas temperature T1. The calculation map M1 stores the relationship between the engine speed NE and the engine load factor KL, which are obtained in advance by experiments or the like, and the steady engine output gas temperature T1.

Further, in the engine output gas temperature estimation process P1, the engine control device 10 corrects the steady engine output gas temperature T1 based on the engine water temperature THW, the outside air temperature THA, the ignition timing SA, and the air-fuel ratio, It is calculated as the value of the exit gas temperature T2.

On the other hand, in the exhaust flow rate calculation process P2, the engine control device 10 calculates the exhaust flow rate GE, which is the flow rate of the exhaust discharged from the combustion chamber 12 to the exhaust passage 14 . The exhaust flow rate GE is calculated as the sum of the intake flow rate GA and the fuel flow rate GF. The fuel flow rate GF is the total amount of fuel injected per unit time. The value of the fuel flow rate GF is obtained from the fuel injection amount Q and the engine speed NE.

Further, in the catalyst inlet gas temperature estimation process P3, the engine control device 10 calculates the catalyst inlet gas temperature T4 based on the engine outlet gas temperature T2, the exhaust flow rate GE, the outside air temperature THA, the running speed V, and the like. The catalyst inlet gas temperature T4 represents the temperature of the exhaust gas flowing into the catalyst device 18 . Note that the engine control device 10 uses a heat balance model for heat exchange between the exhaust passage 14 and the exhaust gas flowing therein, and heat exchange between the exhaust passage 14 and the outside air flowing around the exhaust passage 14 to determine the catalyst-containing gas temperature T4. calculating.

Then, in the catalyst temperature estimation process P4, the engine control device 10 calculates the first catalyst temperature THC1 based on the catalyst inlet gas temperature T4, the exhaust gas flow rate GE, the outside air temperature THA, the traveling speed V, the air-fuel ratio, and the like. The engine control device 10 controls heat exchange between the catalyst device 18 and the exhaust gas flowing inside it, heat exchange between the catalyst device 18 and the outside air flowing around it, and heat generation due to combustion of unburned fuel components in the catalyst device 18. The catalyst temperature is calculated using the heat balance model of

As shown in FIG. 2, when estimating the first catalyst temperature THC1, the engine control device 10 obtains a measured air-fuel ratio AFM, which is a measured value of the air-fuel ratio, from the output λf of the front air-fuel ratio sensor 26 . The engine control device 10 inputs the measured air-fuel ratio AFM as the air-fuel ratio used for calculating the engine output gas temperature T2 in the engine output gas temperature estimation process P1. Further, the engine control device 10 inputs the measured air-fuel ratio AFM as the air-fuel ratio used for calculating the catalyst temperature in the catalyst temperature estimation process P4. Then, in the catalyst temperature estimation process P4, the engine control device 10 obtains the catalyst temperature calculated using the measured air-fuel ratio AFM as the value of the first catalyst temperature THC1. In this embodiment, a series of processes shown in FIG. 2 correspond to the first estimation process.

On the other hand, as shown in FIG. 3, when estimating the second catalyst temperature THC2, the engine control device 10 calculates the air-fuel ratio of the air-fuel mixture combusted in the combustion chamber 12 from the engine load factor KL and the fuel injection amount Q. Specifically, the amount of air flowing into the cylinder, which is the amount of intake air used for combustion in the combustion chamber 12, is obtained from the engine load factor KL, and the ratio of the amount of air flowing into the cylinder to the fuel injection amount Q is used to calculate the air-fuel ratio. It is obtained as a calculated air-fuel ratio AFC value. The engine control device 10 inputs the calculated air-fuel ratio AFC as the air-fuel ratio used for calculating the engine output gas temperature T2 in the engine output gas temperature estimation process P1. Further, the engine control device 10 inputs the calculated air-fuel ratio AFC as the air-fuel ratio used for calculating the catalyst temperature in the catalyst temperature estimation process P4. Then, in the catalyst temperature estimation process P4, the engine control device 10 obtains the catalyst temperature calculated using the calculated air-fuel ratio AFC as the value of the second catalyst temperature THC2. In this embodiment, a series of processes shown in FIG. 3 correspond to the second estimation process.

The engine control device 10 uses the second catalyst temperature THC2 calculated in this way to determine whether the condition for executing abnormality diagnosis of the catalyst device 18 is met. That is, the success or failure of requirement (d) for fulfillment of the execution condition described above is actually determined based on whether or not the second catalyst temperature THC2 is equal to or higher than the diagnostic lower limit temperature.

On the other hand, the engine control device 10 uses the first catalyst temperature THC1 as the catalyst temperature to be referred to in other engine control. For example, the first catalyst temperature THC1 is used to determine whether catalyst warm-up acceleration control and catalyst OT prevention control are to be performed. The catalyst warm-up acceleration control is to warm up the catalyst device 18 by increasing the exhaust gas temperature by retarding the ignition timing SA or the like when the catalyst of the catalyst device 18 is in an inactive state such as immediately after the cold start of the engine 11 . It is a control that promotes the machine. The catalyst OT prevention control is a control that restricts the output of the engine 11 to prevent the catalyst device 18 from overheating when the temperature of the catalyst device 18 becomes too high. The engine control device 10 also uses the first catalyst temperature THC1 as the catalyst temperature for calculating the oxygen storage amount OSA described above.

<Functions and effects of the embodiment>
As described above, in the present embodiment, two temperatures, the first catalyst temperature THC1 and the second catalyst temperature THC2, are obtained as estimated values of the catalyst temperature THC. The first catalyst temperature THC1 is estimated using a measured air-fuel ratio AFM, which is an air-fuel ratio measured by the front air-fuel ratio sensor 26 . On the other hand, the second catalyst temperature THC2 is estimated using a calculated air-fuel ratio AFC, which is an air-fuel ratio calculated from the respective amounts of intake air and fuel used for combustion in the combustion chamber 12 .

On the other hand, in this embodiment, the air-fuel ratio for combustion in the combustion chamber 12 is changed from the stoichiometric air-fuel ratio to an air-fuel ratio other than the stoichiometric air-fuel ratio, and the abnormality diagnosis of the front air-fuel ratio sensor 26 is performed. Until such an abnormality diagnosis is completed and it is confirmed that there is no abnormality, it cannot be denied that the front air-fuel ratio sensor 26 is abnormal. On the other hand, the first catalyst temperature THC1 is obtained using the measured air-fuel ratio AFM, which is the measured value of the air-fuel ratio of the front air-fuel ratio sensor 26 . Therefore, when there is an abnormality in the front air-fuel ratio sensor 26, there is a possibility that a value deviating from the actual catalyst temperature may be obtained as the value of the first catalyst temperature THC1. Therefore, if the first catalyst temperature THC1 is used to determine whether or not the execution condition is satisfied, there is a possibility that the front air-fuel ratio sensor 26 will be diagnosed for abnormality when the actual catalyst temperature is below the diagnosis lower limit temperature. On the other hand, in the present embodiment, whether or not the condition for executing the abnormality diagnosis of the front air-fuel ratio sensor 26 is satisfied is determined using the calculated air-fuel ratio AFC. Therefore, even if there is an abnormality in the front air-fuel ratio sensor 26, abnormality diagnosis is performed under appropriate conditions.

According to the engine control device 10 of the present embodiment described above, the following effects can be obtained.
(1) In the present embodiment, the second catalyst temperature THC2 obtained by using the calculated air-fuel ratio AFC is used to determine whether or not the conditions for executing abnormality diagnosis of the front air-fuel ratio sensor 26 are satisfied. Therefore, even if the front air-fuel ratio sensor 26 is abnormal, the front air-fuel ratio sensor 26 can be diagnosed under appropriate conditions.

(2) During the abnormality diagnosis of the front air-fuel ratio sensor 26, the air-fuel ratio is changed from the stoichiometric air-fuel ratio to another air-fuel ratio. Therefore, if the abnormality diagnosis is performed in a state in which the activity of the catalyst of the catalyst device 18 is insufficient, there is a risk that the properties of the exhaust gas that is released to the outside air will deteriorate. In this regard, in the present embodiment, even if there is an abnormality in the front air-fuel ratio sensor 26, the abnormality diagnosis is not performed when the catalyst temperature is below the diagnosis lower limit temperature. Therefore, it is possible to appropriately suppress the deterioration of the exhaust property during the abnormality diagnosis.

This embodiment can be implemented with the following modifications. This embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
・If the measured air-fuel ratio AFM is used to calculate the first catalyst temperature THC1 and the calculated air-fuel ratio AFC is used to calculate the second catalyst temperature THC2, the details of the estimation logic may be changed as appropriate. good.

The second catalyst temperature THC2 may be used for purposes other than the determination of whether or not the execution conditions for diagnosing an abnormality of the front air-fuel ratio sensor 26 are met. For example, the engine is controlled using the second catalyst temperature THC2 until the abnormality diagnosis is completed. After the abnormality diagnosis is completed and it is confirmed that the front air-fuel ratio sensor 26 is functioning normally, the first catalyst temperature THC1 may be used for engine control.

DESCRIPTION OF SYMBOLS 10... Engine control apparatus 11... Engine 12... Combustion chamber 13... Intake passage 14... Exhaust passage 15... Throttle valve 16... Injector 17... Ignition device 18... Catalyst device 19... Filter device 20... Processing unit 21... Storage device 22... Airflow meter 23 Throttle opening sensor 24 Intake pressure sensor 25 Crank angle sensor 26 Front air-fuel ratio sensor 27 Rear air-fuel ratio sensor 28 Accelerator pedal sensor 29 Vehicle speed sensor 30 Water temperature sensor

Claims (1)

An engine control device for diagnosing an abnormality of an air-fuel ratio sensor in an engine in which an air-fuel ratio sensor and a catalytic device for purifying exhaust gas are installed in an exhaust passage through which exhaust gas generated by combustion of an air-fuel mixture in a combustion chamber flows, wherein ,
The engine control device performs, as processing for estimating the catalyst temperature of the catalyst device,
a first estimation process of estimating the catalyst temperature using the air-fuel ratio measured by the air-fuel ratio sensor;
a second estimation process for estimating the catalyst temperature using an air-fuel ratio calculated from each amount of intake air and fuel used for combustion in the combustion chamber;
and the condition for executing the abnormality diagnosis of the air-fuel ratio sensor includes that the estimated value of the catalyst temperature obtained by the second estimation process is equal to or higher than a predetermined diagnostic lower limit temperature. Engine control device .

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