JP2022006360A - Air-fuel ratio control device - Google Patents

Abstract

To provide an air-fuel ratio control device capable of preventing cracking of an exhaust sensor due to exposure to water, and early raising a temperature of the exhaust sensor.SOLUTION: An air-fuel ration control device 1 comprises: an air-fuel ratio sensor 6; a heater 9 which raises a temperature of the air-fuel sensor; a sensor 8 which measures a temperature of the air-fuel ratio sensor; a sensor 11 which measures a temperature of cooling water at a start-up of an engine; a sensor 12 which measures a temperature of intake air of the engine; and an ECU 2 which controls the heater and determines predetermined time required to control the heater on the basis of the measured temperatures of the cooling water and the intake air. The ECU 2 controls the heater so as to increase the temperature of the air-fuel ratio sensor to a predetermined temperature lower than a target temperature during a period from when an ignition is turned on to when the engine is started up, and controls the heater so as to increase the temperature of the air-fuel ratio sensor to the target temperature when a period where a decrease in the temperature of the air-fuel ratio sensor is equal to or less than a predetermined value lasts for the predetermined period or longer after the engine is started up.SELECTED DRAWING: Figure 1

Description

The present invention relates to an air-fuel ratio control device.

There is known an air-fuel ratio control device for an internal combustion engine that activates the exhaust sensor as soon as possible after starting the engine and starts air-fuel ratio feedback control while preventing the exhaust sensor from cracking due to water exposure (for example, a patent). See Document 1).

In Patent Document 1, the air-fuel ratio control device reads the cooling water temperature Tw at the time of starting the engine, calculates the basic heater energization prohibition period Ls based on the cooling water temperature Tw, and cools the cooling water temperature at the time of stopping the engine operation and cooling at the time of starting the engine. The temperature difference ΔT with the water temperature is calculated. Further, the period correction coefficient H is calculated based on the temperature difference ΔT, and the basic heater energization prohibition period Ls is multiplied by the period correction coefficient H to calculate the final heater energization prohibition period L. After the heater energization prohibition period L has elapsed from the start of the engine, energization of the heater is started to perform air-fuel ratio feedback control.

Japanese Unexamined Patent Publication No. 2010-77848

The above method of calculating the energization prohibition period of the heater that heats the element of the exhaust sensor based on the information of the temperature difference ΔT and the cooling water temperature Tw does not reflect the information of the environmental temperature, and the engine and the exhaust manifold are cooled. It is not possible to calculate the energization prohibition period of the heater with high accuracy reflected. In addition, the heater prohibition period also differs depending on the difference in the operation pattern after the engine is started.

Therefore, it is necessary to take a large margin for the heater prohibition period, and it may take time to raise the temperature of the exhaust sensor.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an air-fuel ratio control device capable of preventing the exhaust sensor from cracking due to water exposure and raising the temperature of the exhaust sensor at an early stage.

In order to achieve the above object, the air-fuel ratio control device disclosed in the specification includes an engine exhaust sensor, a temperature raising device for raising the temperature of the exhaust sensor, and a first temperature sensor for measuring the temperature of the exhaust sensor. A second temperature sensor that measures the temperature of the cooling water at the start of the engine, a third temperature sensor that measures the temperature of the intake air of the engine, and the second temperature sensor that controls the temperature riser and the second temperature sensor. The control means comprises a control means for determining a predetermined time used for controlling the temperature raising device based on the temperature of the cooling water measured in the above and the temperature of the intake air measured by the third temperature sensor. During the period from the ignition on to the start of the engine, the temperature riser is controlled so as to raise the temperature to a predetermined temperature lower than the target temperature, and after the engine is started, the temperature of the exhaust sensor drops below a predetermined value. It is characterized in that the temperature raising device is controlled so as to raise the temperature of the exhaust sensor to the target temperature when a certain period continues for the predetermined time or more.

It is possible to prevent the exhaust sensor from cracking due to water exposure and to raise the temperature of the exhaust sensor at an early stage.

It is a block diagram of the air-fuel ratio control device which concerns on this embodiment. It is a figure which shows an example of 2D map data. It is a flowchart which shows the process of an ECU. It is a figure which shows an example of the time chart corresponding to the flowchart shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an air-fuel ratio control device according to the present embodiment. The air-fuel ratio control device 1 according to the present embodiment includes an A / F (air-fuel ratio) sensor 6 which is an exhaust sensor, an ECU (Electronic Control Unit) 2 (control means) that controls the A / F sensor 6, and an engine. The cooling water temperature sensor 11 (second temperature sensor) for measuring the temperature of the cooling water of the engine and the intake air temperature sensor 12 (third temperature sensor) for measuring the temperature of the intake air of the engine are provided. The exhaust sensor is not limited to the A / F sensor 6, and may be another sensor that detects a specific component in the exhaust.

The ECU 2 includes a microcomputer (hereinafter, simply referred to as a microcomputer) 3 composed of a CPU (Central Processing Unit) (not shown), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, a sensor circuit 4, and a sensor circuit 4. It includes a heater control circuit 5, an A / D converter, a D / A converter, and the like (not shown).

The A / F sensor 6 includes a sensor element 7, an element temperature sensor 8 (first temperature sensor) for measuring the temperature of the sensor element 7, a heater 9 (heating device) for raising the temperature of the sensor element 7, and a sensor element. It is provided with a cover (not shown) that covers 7.

The A / F sensor 6 is provided in the exhaust system of an engine (not shown), and the engine and the ECU 2 are mounted in a vehicle (not shown). When the capacity of the battery 10 is large, preheat control for energizing the heater 9 can be preferably performed before the engine is started. Thereby, the activation of the sensor element 7 can be accelerated.

The sensor element 7 is exposed to water in the exhaust system of the engine as follows. For example, when the engine is stopped, water vapor condenses in the exhaust system as the temperature drops. After the engine is restarted, such dew condensation water rides on the exhaust and reaches the sensor element 7. That is, the sensor element 7 may be exposed to water in this way, for example. Further, after the engine is started, when the exhaust comes into contact with the cover of the A / F sensor 6, the water vapor in the exhaust is cooled by the cover and dew condensation occurs. The dew condensation water generated in this way enters the cover together with the exhaust gas and reaches the sensor element 7. That is, the sensor element 7 may be exposed to water in this way.

In order to detect the output of the A / F sensor 6, the microcomputer 3 inputs a predetermined signal to the sensor circuit 4, and the sensor circuit 4 applies a voltage to the sensor element 7 based on the input signal. The microcomputer 3 detects the current flowing through the sensor element 7 through the sensor circuit 4 according to the oxygen concentration in the exhaust gas when the voltage is applied.

The heater control circuit 5 controls the energization of the heater 9 under the control of the microcomputer 3. When the heater control circuit 5 is controlled so that the microcomputer 3 energizes the heater 9, electric power is supplied from the battery 10 to the heater 9. At the same time, the microcomputer 3 controls the heater control circuit 5 to duty-control the energization of the heater 9. Further, the microcomputer 3 detects the current and voltage of the heater 9 via the heater control circuit 5.

As described above, the A / F sensor 6 (more specifically, the heater 9) is electrically connected to the ECU 2 as a control target. Further, the cooling water temperature sensor 11 and the intake air temperature sensor 12 are electrically connected to the ECU 2.

The ROM stores programs, map data, and the like in which various processes executed by the CPU are described. Based on the program stored in the ROM, the CPU executes processing while using the temporary storage area of the RAM as needed, so that the ECU 2 functions as a control means.

The ECU 2 starts energizing the heater 9 when the ignition is turned on, for example. That is, the ECU 2 performs preheat control to energize the heater 9 before starting the engine.

After that, the ECU 2 starts fine energization to the heater 9 after the engine is started. During the period of preheat control and micro-energization, energization control is executed so that the temperature of the sensor element 7 is lower than the temperature at which element cracking due to water exposure occurs (allowable limit temperature).

After the engine is started, the ECU 2 monitors the presence or absence of water on the sensor element 7 from the transition of the temperature of the sensor element 7. If the sensor element 7 is covered with water, the temperature of the sensor element 7 drops. If the sensor element 7 is not covered with water for a predetermined time (specifically, a specified value specified in the two-dimensional map data of FIG. 2 to be described later), the ECU 2 fully energizes the heater 9. The start is made so that the sensor element 7 is activated promptly, and then feedback (FB) control is performed. In the FB control, the heater 9 is energized to control the temperature of the sensor element 7 to the target temperature according to the full energization. The target temperature is set to a predetermined active temperature of the sensor element 7.

FIG. 2 is a diagram showing an example of two-dimensional map data that defines a determination value (predetermined time) for starting full energization of the heater 9. This two-dimensional map data is stored in a ROM (not shown) in the microcomputer 3. The two-dimensional map data defines a determination value (predetermined time) for starting full energization of the heater 9 based on the temperature of the cooling water at the start of the engine and the temperature of the intake air of the engine. “A001, a002, ..., Axxx” in FIG. 2 indicate a determination value (predetermined time).

The ECU 2 (specifically, the microcomputer 3) uses the cooling water temperature at the start of the engine measured by the cooling water temperature sensor 11, the temperature of the intake air of the engine measured by the intake air temperature sensor 12, and the two-dimensional map data. Based on this, a predetermined time for starting full energization is determined, and if the sensor element 7 is not covered with water for the determined predetermined time or longer after the engine is started, full energization of the heater 9 is started.

FIG. 3 is a flowchart showing the processing of the ECU 2. The ECU 2 repeatedly executes the process shown in the flowchart of FIG. 3 at very short time intervals. This flowchart is started after the engine is stopped.

First, the ECU 2 determines whether or not the ignition is ON (IG-ON) (S1). If NO in S1, this process ends. If YES in S1, the ECU 2 determines whether or not the engine has been started (S2). If NO in S2, it means that the engine has not been started, so the ECU 2 starts preheat control (S3). The ECU 2 starts measuring the temperature of the sensor element 7 using the element temperature sensor 8 (S4), and ends this process.

If YES in S2, it means that the engine has been started, so the ECU 2 starts fine energization to the heater 9 (S5). During the period of preheat control and micro-energization, energization control is executed so that the temperature of the sensor element 7 is lower than the temperature at which element cracking due to water exposure occurs (allowable limit temperature).

Next, the ECU 2 determines whether or not the temperature drop of the sensor element 7 is equal to or less than a predetermined value (S6). The temperature drop of the sensor element 7 indicates, for example, the difference between the temperature of the sensor element 7 before the engine is started and the temperature of the sensor element 7 which is lowered due to the water exposure after the engine is started. That is, if the temperature drop of the sensor element 7 due to water exposure exceeds a predetermined value after the engine is started, the determination of S6 becomes NO. If the temperature drop of the sensor element 7 is not more than a predetermined value due to drying after the engine is started, the determination of S6 is YES. If NO in S6, the sensor element 7 is not yet dried, and this process is terminated. If YES in S6, the ECU 2 determines whether or not the period (T1) in which the temperature drop of the sensor element 7 is equal to or less than a predetermined value continues for a predetermined time or more specified in the two-dimensional map data (S7). ). In S7, it is determined whether or not the period in which the dew condensation water evaporates and the sensor element 7 is dry continues for a predetermined time or longer. If NO in S7, this process ends.

If YES in S7, the ECU 2 starts full energization of the heater 9, performs FB control so that the temperature of the sensor element 7 reaches the target temperature (S8), and ends this process.

FIG. 4 is a diagram showing an example of a time chart corresponding to the flowchart shown in FIG.

When the ignition is turned on, preheat control is started. Then, after the engine is started, micro-energization is started. During the period of preheat control and micro-energization, energization control is executed so that the temperature of the sensor element 7 becomes lower than the allowable limit temperature.

After the engine is started, when the period (T1) in which the temperature drop of the sensor element 7 is equal to or less than a predetermined value continues for a predetermined time or more specified in the two-dimensional map data, the ECU 2 fully energizes the heater 9. Start and perform FB control so that the temperature of the sensor element 7 reaches the target temperature.

As described above, according to the present embodiment, the period during which the sensor element 7 is presumed to be flooded (for example, the temperature of the intake air of the engine) is estimated with reference to the information on the environmental temperature (for example, the temperature of the intake air of the engine). During the period T1), the fine energization is continued until the dew condensation water evaporates, and the temperature of the sensor element 7 is maintained at the limit allowable temperature at which the element crack does not occur, so that the element crack can be prevented. Further, since the start timing of full energization of the heater 9 is determined with reference to the information on the environmental temperature, the temperature of the sensor element 7 can quickly reach a predetermined target temperature (active temperature), and the sensor can be used. The element 7 can be activated at an early stage.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiment, and various modifications are made within the scope of the gist of the present invention described in the claims.・ Can be changed.

1 air-fuel ratio controller, 2 ECU, 3 microcomputer, 4 sensor circuit 4, 5 heater control circuit, 6 A / F sensor, 7 sensor element, 8 element temperature sensor, 9 heater, 11 cooling water temperature sensor, 12 intake air temperature sensor

Claims (1)

The exhaust sensor of the engine and
A temperature raising device that raises the temperature of the exhaust sensor, and
The first temperature sensor that measures the temperature of the exhaust sensor and
A second temperature sensor that measures the temperature of the cooling water when the engine is started,
A third temperature sensor that measures the temperature of the intake air of the engine,
A predetermined time used to control the temperature riser and to control the temperature riser based on the temperature of the cooling water measured by the second temperature sensor and the temperature of the intake air measured by the third temperature sensor. With control means to determine,
The control means controls the temperature riser so as to raise the temperature to a predetermined temperature lower than the target temperature from the ignition on to the start of the engine.
After starting the engine, when the period in which the temperature drop of the exhaust sensor is equal to or less than a predetermined value continues for the predetermined time or longer, the temperature raising device is controlled so as to raise the temperature of the exhaust sensor to the target temperature. An air-fuel ratio control device characterized by.

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