JP2003161202A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To activate a sensor by heater operation and to control an engine accurately by the sensor in a control device for an internal combustion engine equipped with the sensor installed in an engine exhaust system through which exhaust gas containing particulates passes and a heater for heating the sensor, while prohibiting the operation of the heater for a while after starting of the engine. <P>SOLUTION: The heating time by the heater required for providing an accurate output of the sensor is determined in consideration (step 107 and 108) of the adhesion of the particulates to the sensor at the time of starting the heater (step 105). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine.

[0002]

2. Description of the Related Art Various sensors for detecting the state of exhaust gas are arranged in an engine exhaust system. For example, in order to grasp the combustion air-fuel ratio, an oxygen sensor for detecting the oxygen concentration in the exhaust gas is arranged in the engine exhaust system. Certain sensors, such as oxygen sensors, have a relatively high activation temperature and require a long time from engine start to activation using the heat of the exhaust gas. In order to activate the sensor early and enable control using the sensor immediately after engine startup, the sensor is equipped with a heater that heats itself, and the heater is activated from engine startup to activate the sensor early. Is proposed.

When the engine is started, the temperature of the entire engine exhaust system is low, and water vapor in the exhaust gas is condensed in the engine exhaust system. If the condensed water adheres to the sensor heated by the heater, the sensor may be cooled rapidly and may be mechanically damaged by the rapid temperature change.

Japanese Unexamined Patent Publication No. 2001-41923 discloses that a heater provided in a sensor is not operated until the temperature of the engine exhaust system rises at the time of engine startup and the water condensed in the engine exhaust system evaporates. is doing. After that, the control by the sensor is performed when the heating for a predetermined time required to activate the heater and activate the sensor is completed. After that, the heater is energized and controlled so as to keep the sensor active.

[0005]

According to the above-mentioned conventional technique, it is possible to prevent mechanical damage of the sensor due to a sudden temperature change. However, in an internal combustion engine such as a diesel engine and a direct injection gasoline engine in which exhaust gas contains particulates, accurate control may not be realized even if a sensor is activated by heating for a predetermined time.

Therefore, an object of the present invention is to provide a sensor provided in an engine exhaust system through which exhaust gas containing particulates passes, and a heater for heating the sensor, and activate the heater for a while after the engine is started. In a control device for an internal combustion engine that does not allow it, the sensor is activated by the operation of the heater, and accurate control by the sensor can be surely realized.

[0007]

A control device for an internal combustion engine according to a first aspect of the present invention includes a sensor provided in an engine exhaust system through which exhaust gas containing particulates passes,
A controller for an internal combustion engine, comprising: a heater for heating the sensor, wherein the heater is not operated for a while after the engine is started, in order to prevent particulate adhesion to the sensor at the time of starting the operation of the heater. In consideration of the above, the heating time of the heater until the sensor provides an accurate output is determined.

According to a second aspect of the present invention, there is provided a control device for an internal combustion engine according to the first aspect, wherein the particulate matter adheres to the sensor at the time of starting the operation of the heater. The amount of heat is estimated, and the heating time is lengthened as the estimated amount of particulate adhesion increases.

[0009]

1 shows a diesel engine equipped with a control device according to the present invention, and exhaust gas contains particulates. Reference numeral 1 is an engine body, 2 is an engine intake system communicating with the cylinder through an intake valve 3, and 4 is an engine exhaust system communicating with the cylinder through an exhaust valve 5. 6 is a combustion chamber 7a formed on the top surface of the piston 7.
A fuel injection valve for injecting fuel into the interior. An oxygen sensor 8 whose output voltage changes according to the oxygen concentration in the exhaust gas is arranged in the engine exhaust system in order to grasp the combustion air-fuel ratio. In order to grasp only whether the combustion air-fuel ratio is rich or lean, a step output type oxygen sensor in which the output voltage suddenly changes when the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio is used. Further, in order to grasp the degree of combustion air-fuel ratio rich or lean, a linear output type oxygen sensor whose output voltage changes linearly according to the air-fuel ratio of exhaust gas is used.

Each of the oxygen sensors has a relatively high activation temperature (about 650 ° C.), and a heater for raising the activation temperature is provided. When the engine is started, the temperature of the entire engine exhaust system is low, and in order to start the combustion air-fuel ratio control (fuel injection amount control or intake air amount control) that uses the oxygen sensor, the above heater must be operated. I have to. Reference numeral 20 denotes a control device, which controls the operation of the heater while performing the air-fuel ratio by the oxygen sensor 8. A temperature sensor 9 for detecting the temperature near the position of the oxygen sensor 8 in the engine exhaust system 4, a water temperature sensor 10 for detecting the temperature of the engine cooling water, etc. are electrically connected.

FIG. 2 is a flowchart which is executed by the present controller to operate the heater immediately after the engine is started. This flowchart is started at the same time when the engine start is completed, and is repeated every predetermined time. First, in step 101, it is determined whether the flag F is 1. The flag F is reset to 0 at the same time when the engine is stopped. At the beginning of the engine start, this determination is denied and the routine proceeds to step 102.

In step 102, the temperature T of the engine exhaust system is
H is detected by the temperature sensor 9 described above. Then
In step 103, it is determined whether the detected temperature TH is equal to or higher than the set temperature TH1. When this judgment is denied, it is considered that the water vapor in the exhaust gas is condensed in the engine exhaust system. As a result, if the heater is operated to heat the oxygen sensor 8, the water condensed in the engine exhaust system adheres to the oxygen sensor 8 and the oxygen sensor 8 is rapidly cooled, and this rapid temperature change occurs. As a result, the oxygen sensor 8 is mechanically damaged.

In order to prevent this, when the determination in step 103 is negative in this flowchart, the particulate adhesion amount S is increased by the set amount a in step 104 without activating the heater, and the process ends. As described above, the exhaust gas of the diesel engine contains particulates, and the particulates adhere to the oxygen sensor 8. The set amount a is
The amount of particulates newly attached to the oxygen sensor at the execution intervals of this flowchart, and the amount S of particulates attached represents the amount of particulates currently attached to the oxygen sensor. This particulate adhesion amount S is stored without being reset even when the engine is stopped.

While this series of processes is repeated, the temperature TH of the engine exhaust system is heated by the passing exhaust gas and is raised.
Becomes equal to or higher than the set temperature TH1 and the determination in step 103 is affirmed. At this time, the water condensed in the engine exhaust system has not evaporated and the step 105
The heater is activated at. Of course, in the start when the outside air temperature is high or the restart immediately after the engine is stopped, the determination in step 103 is affirmed from the beginning, and the heater is immediately activated in step 105.

Next, at step 106, it is judged if the elapsed time t from the heater operation is equal to or longer than the set time t1. Initially, this determination is denied, and in step 104, the amount S of particulates adhering to the oxygen sensor 8 is integrated and the process ends. The particulates adhering to the oxygen sensor 8 are the activation temperature of the oxygen sensor 8 (650
Since it does not ignite and burn unless the temperature reaches the same level as (° C), at the beginning of heating the oxygen sensor 8 by the heater,
Particulates in the exhaust gas newly attach to the oxygen sensor 8.

When this series of processes is repeated, the heater is operated for the set time t1 and the determination in step 106 is affirmed. At this time, the oxygen sensor 8 is at the activation temperature. However, at this time, the oxidation of SOF adhering to the oxygen sensor 8 and the combustion of particulates have started, and even if the combustion air-fuel ratio control of the internal combustion engine by the oxygen sensor is started at this point, accurate control cannot be realized. is there. This is because even if the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, oxygen is consumed around the oxygen sensor 8 as the particulates burn, so that the oxygen sensor 8 has a true air-fuel ratio of the exhaust gas. It is not always output that the value is richer than the value and that it is leaner than the theoretical air-fuel ratio.

In this flowchart, the control of the internal combustion engine by the oxygen sensor 8 is not started immediately when the determination in step 106 is affirmative, but step 107 is performed.
At step 108, the set amount b is reduced from the accumulated amount S of particulates adhering to the oxygen sensor 8, and it is determined in step 108 whether or not the amount S of particulates adhering becomes 0 or less. This set amount b is the amount of particulates burned on the oxygen sensor 8 at the execution intervals of this flowchart.

When the determination in step 108 is negative, the oxygen sensor 8 has particulates adhering to it, and the particulates are in the process of burning. At this time also, the particulates in the exhaust gas are fresh. Adhere to the oxygen sensor 8. Thereby, step 104
At the particulate adhesion amount S, the above-mentioned set amount a
Is added and the process ends. Of course, the amount of particulates burned on the oxygen sensor per unit time is considerably larger than the amount of particulates newly attached to the oxygen sensor 8. If this series of processes is repeated, the determination in step 108 is surely made. Affirmed.

When the determination in step 108 is affirmative, in step 109, the combustion air-fuel ratio control of the internal combustion engine using the oxygen sensor 8 is started. At this point, the particulates on the oxygen sensor 8 have been completely burned down, so the output of the oxygen sensor is accurate, and accurate combustion air-fuel ratio control using the oxygen sensor 8 is possible. Next, at step 110, the above-mentioned flag F is set to 1. After that, step 101
Since the determination in (1) is affirmed, unless the flag F is reset to 0 by the engine stop, the processing of this flowchart described so far is not repeated.

Following the heater operation control according to this flowchart, the normal heater operation control is executed. This normal heater operation control is to maintain the oxygen sensor in the vicinity of the activation temperature by operating the heater or the like when it is determined that the temperature of the exhaust gas has decreased based on the engine operating state. In this way, since the oxygen sensor 8 is maintained at the activation temperature, the particulates adhering to the oxygen sensor 8 are immediately burned out thereafter. This momentary burning of a small amount of particulates hardly changes the oxygen concentration around the oxygen sensor 8.

In the above-mentioned flow chart, the temperature TH of the engine exhaust system is detected and used to judge whether water is condensed in the engine exhaust system, but this does not limit the present invention. For example, when starting the engine, the water temperature sensor 1
0 to detect the engine cooling water temperature, or to detect the outside air temperature and the like, and based on this detected temperature, the temperature T of the engine exhaust system.
H may be estimated and used, or the detected cooling water temperature or outside air temperature may be directly used. As described above, when the engine is restarted immediately after it is stopped, the temperature of the engine exhaust system is high and no dew condensation occurs in the engine exhaust system. Accordingly, when the difference between the engine cooling water temperature detected at the engine start and the outside air temperature is equal to or higher than the predetermined temperature, it may be determined that the engine is restarted immediately after the engine is stopped and the heater may be operated immediately. Further, in this flow chart, the temperature TH of the engine exhaust system is also detected and used to determine whether or not the moisture condensed in the engine exhaust system is evaporated, but it is detected, for example, when the engine is started. Based on the engine cooling water temperature or the outside air temperature, it may be determined whether or not the dew condensation water in the engine exhaust system has evaporated, in consideration of the operating state and the elapsed time immediately after the engine is started. Here, the lower the engine cooling water temperature or the outside air temperature, the longer the elapsed time until this determination is affirmed, and the higher the exhaust gas temperature based on the operating state after engine start, this determination is affirmed. The elapsed time to become shorter. Further, when the difference between the engine cooling water temperature and the outside air temperature becomes equal to or higher than a predetermined temperature, it may be determined that the temperature of the engine exhaust system is sufficiently increased and the dew condensation water is not evaporated.

In this flowchart, the oxygen sensor 8
The operating time of the heater until the temperature reaches the activation temperature is set as the set time t1.
If the determination in 03 is affirmative, the higher the engine exhaust system temperature TH, the higher the temperature of the oxygen sensor itself from the beginning, so the set time t1 may be shortened.

Further, in this flow chart, the amount S of particulates adhering to the oxygen sensor at the time of starting the operation of the heater, if the combustion air-fuel ratio control by the oxygen sensor is started at the previous engine start (step 1
If the engine is stopped before the determination of step 08 is affirmed), the particulate adhesion amount S at this time is stored, and thus the stored particulate adhesion amount S is stored at the time of the engine startup this time. Used as the initial value.
Therefore, even in such a case, step 10
When the determination in 8 is affirmative, the oxygen sensor 8 is not attached with particulates.

As described above, this flowchart estimates the amount of particulates adhering to the oxygen sensor at the time of starting the operation of the heater, and the more the estimated amount of particulates adhering to the oxygen sensor, the more accurate the oxygen sensor outputs. The operation time of the heater before providing is determined to be long. Practically, in this flowchart, the amount of particulates adhering to the oxygen sensor at each time from the engine startup to the start of the combustion air-fuel ratio control by the oxygen sensor is accurately grasped. However, since the time for burning off the particulate matter adhering to the oxygen sensor does not become so long, for example, while the heater is operating for the set time t1, the accumulation of the particulate matter adherence amount S may be omitted. That is, while the determination in step 106 is denied, the process may end as it is.

To estimate the amount of particulate adhered, the amount of particulate newly attached at each execution interval of the flow chart is set as the set amount a at step 104, and this is added up. It may be changed in consideration of the difference in the particulate discharge amount discharged from the combustion chamber based on the state.

Further, when the heater is not operated for a while after the engine is started, rather than accurately grasping the amount of particulates adhering to the oxygen sensor at each time, it is determined that the particulates are adhering to the oxygen sensor. , Even if the heating time of the heater until the oxygen sensor provides an accurate output is simply lengthened by a predetermined time, the particulates can be burnt out in this predetermined time, and good combustion air-fuel ratio control by the oxygen sensor is possible. Can be realized.

According to the present embodiment, as shown in the time chart of FIG. 3, the oxygen sensor is operated by the dew condensation in the engine exhaust system in the shortest time after stopping the operation of the heater from the timing A when the engine start is completed. From the time when this is realized, the heater is activated to activate the oxygen sensor, and the particulates on the oxygen sensor are burned off. Based on the accurate output of the oxygen sensor from time C when this is realized. The combustion air-fuel ratio control is started. In comparison with this, conventionally, since the adherence of particulates to the oxygen sensor is not taken into consideration, the output of the oxygen sensor is inaccurate at the time C ′ when the heater is activated and the oxygen sensor is activated from the time B. Nevertheless, the combustion air-fuel ratio control by the oxygen sensor was started.

In another conventional technique, as shown in the time chart of FIG. 4, for example, it is predetermined that the combustion air-fuel ratio control by the oxygen sensor is started when the cooling water temperature reaches a predetermined temperature. In the engine controller,
The combustion air-fuel ratio control start timing is set so that the oxygen sensor is activated in synchronization with this combustion air-fuel ratio control start (timing C) in order to secure the longest possible time for removing the water condensed in the engine exhaust system. Since then, the heater is activated (timing B ′) as soon as necessary for activation. When the present invention is applied to such a control device for an internal combustion engine, in order to enable accurate combustion air-fuel ratio control, it is necessary to activate the oxygen sensor from the start time (time C) of the combustion air-fuel ratio control. That is, the heater is activated (timing B) earlier than the total time required for burning out the particulates adhering to the oxygen sensor.

So far, the case where the oxygen sensor is arranged in the engine exhaust system has been described. However, this does not limit the present invention.For example, even when another sensor such as a pressure sensor exposed to exhaust gas is arranged in the engine exhaust system, this sensor activates itself at an activation temperature. It has a heater to raise the temperature, and to prevent mechanical damage due to dew condensation water, this heater is not activated for a while after the engine is started, and the adherence of particulates to this sensor If it interferes with the accurate output of the heater, the heating time of the heater until the sensor provides the accurate output is determined in consideration of the adherence of particulates to the sensor when the heater is started. By doing so, accurate control by the sensor becomes possible. Further, the internal combustion engine to which the present invention is applicable,
The present invention is not limited to the diesel engine, and may be a spark ignition internal combustion engine capable of stratified combustion, for example, as long as the exhaust gas contains particulates.

[0030]

The control device for an internal combustion engine according to the present invention comprises a sensor provided in an engine exhaust system through which exhaust gas containing particulates passes, and a heater for heating this sensor. In an internal combustion engine control device that does not operate the heater for a while, determines the heating time of the heater until the sensor provides an accurate output in consideration of the adhesion of particulates to the sensor at the time of starting the operation of the heater. It is supposed to do. While the heater is not activated, particulate matter in the exhaust gas adheres to the sensor, and even if the sensor is activated, it cannot provide an accurate output until the particulate matter is burned out. According to the control device of the engine, since the heating time of the heater is determined in consideration of the adhesion of particulates to the sensor, the particulates can be burned out after this heating time, and accurate control by the sensor can be performed. It is possible to realize it without fail.

[Brief description of drawings]

1 is a schematic view of an internal combustion engine equipped with a control device according to the present invention.

FIG. 2 is a flowchart showing a heater operation control executed by a control device according to the present invention.

FIG. 3 is a time chart comparing the heater operation control in the control device according to the present invention with the conventional heater operation control.

FIG. 4 is another time chart comparing the heater operation control in the control device according to the present invention with the conventional heater operation control.

[Explanation of symbols]

1 ... Engine body 2 ... Engine intake system 3 ... Engine exhaust system 8 ... Oxygen sensor 20 ... Control device

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masaaki Kobayashi             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Satoshi Nakamura             14 Iwatani Shimohakaku-cho, Nishio-shi, Aichi Stock Association             Company Japan Auto Parts Research Institute F term (reference) 3G084 AA00 AA01 BA00 BA09 CA01                       CA02 DA00 DA04 DA30 EB03                       FA20 FA27 FA29

Claims (2)

[Claims] 1. A sensor provided in an engine exhaust system through which exhaust gas containing particulates passes, and a heater for heating the sensor, and the heater is not operated for a while after the engine is started. In a control device for an internal combustion engine, the heating time of the heater is determined until the sensor provides an accurate output in consideration of particulate adhesion to the sensor at the time of starting the operation of the heater. Control device for internal combustion engine. 2. The amount of particulates adhered to the sensor at the time of starting the operation of the heater is estimated, and the heating time is lengthened as the estimated amount of particulates adhered increases. The control device for an internal combustion engine according to claim 1.