JP3990902B2 - Control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for an internal combustion engine.
[0002]
[Prior art]
Various sensors for detecting the state of exhaust gas are arranged in the 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. Some types of sensors such as oxygen sensors have a relatively high activation temperature, and a long time is required from the start of the engine to the 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 provided with a heater that heats itself, and the sensor is activated early by operating the heater from the time of engine startup Has been proposed.
[0003]
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. When the condensed moisture adheres to the sensor heated by the heater, the sensor is rapidly cooled and may be mechanically damaged by the rapid temperature change.
[0004]
Japanese Patent Laid-Open No. 2001-41923 discloses that the heater provided in the sensor is not operated until the temperature of the engine exhaust system rises at the time of engine startup and moisture condensed in the engine exhaust system evaporates. . Thereafter, the sensor is controlled from the time when heating for a predetermined time necessary to activate the sensor by operating the heater is completed. Thereafter, the heater is energized and controlled so as to maintain the active state of the sensor.
[0005]
[Problems to be solved by the invention]
According to the above-described conventional technology, it is possible to prevent mechanical damage to 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 particulates are contained in exhaust gas, accurate control may not be realized even if the sensor is activated by heating for a predetermined time.
[0006]
Accordingly, 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 so that the heater is not operated for a while after the engine is started. In the control apparatus for an internal combustion engine, the sensor is activated by the heater operation, and accurate control by the sensor can be realized with certainty.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a control apparatus for an internal combustion engine, comprising: a sensor provided in an engine exhaust system through which exhaust gas containing particulates passes; and a heater for heating the sensor; In the control apparatus for an internal combustion engine that prevents the heater from being operated for a while, the sensor 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. The heating time of the heater is determined.
[0008]
According to a second aspect of the present invention, there is provided the control apparatus for an internal combustion engine according to the first aspect, wherein the amount of particulate adhering to the sensor when the heater is started is estimated. The heating time is longer as the estimated particulate adhesion amount is larger.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a diesel engine to which a control device according to the present invention is attached, and exhaust gas contains particulates. Reference numeral 1 denotes an engine main body, 2 an engine intake system that communicates with the cylinder via the intake valve 3, and 4 an engine exhaust system that communicates with the cylinder via the exhaust valve 5. Reference numeral 6 denotes a fuel injection valve for injecting fuel into the combustion chamber 7 a formed on the top surface of the piston 7. In the engine exhaust system, an oxygen sensor 8 whose output voltage changes depending on the oxygen concentration in the exhaust gas is disposed 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 changes suddenly when the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio is used. Further, in order to grasp the richness or leanness of the combustion air-fuel ratio, a linear output type oxygen sensor whose output voltage changes linearly according to the air-fuel ratio of the exhaust gas is used.
[0010]
All of the oxygen sensors have a relatively high activation temperature (about 650 ° C.), and a heater for raising the temperature to this activation temperature is provided. When the engine is started, the entire engine exhaust system is at a low temperature. In order to start combustion air-fuel ratio control (fuel injection amount control or intake air amount control) using an oxygen sensor, the above-mentioned heater must be operated. I must. Reference numeral 20 denotes a control device that performs the air-fuel ratio by the oxygen sensor 8 and controls the operation of the heater. A temperature sensor 9 for detecting the temperature in the vicinity of the position of the oxygen sensor 8 in the engine exhaust system 4 and a water temperature sensor 10 for detecting the temperature of the engine cooling water are electrically connected.
[0011]
FIG. 2 is a flowchart executed for operating the heater immediately after the engine is started by the control device. 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 or not the flag F is 1. The flag F is reset to 0 at the same time as the engine is stopped. At the beginning of the engine start, this determination is denied and the routine proceeds to step 102.
[0012]
In step 102, the temperature TH of the engine exhaust system is detected by the temperature sensor 9 described above. Next, at step 103, it is determined whether or not the detected temperature TH is equal to or higher than a set temperature TH1. When this judgment is denied, it is considered that water vapor in the exhaust gas is condensed in the engine exhaust system. Accordingly, if the oxygen sensor 8 is heated by operating the heater, moisture 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.
[0013]
In order to prevent this, in the flowchart, when the determination in step 103 is negative, the particulate adhesion amount S is increased by the set amount a in step 104 without activating the heater, and the process is terminated. As described above, the exhaust gas of the diesel engine contains particulates, and these 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 interval of this flowchart, and the particulate attachment amount S represents the amount of particulates currently attached to the oxygen sensor. The particulate adhesion amount S is stored without being reset even when the engine is stopped.
[0014]
While this series of processing is repeated, the engine exhaust system is heated by the passing exhaust gas, so that the temperature TH of the engine exhaust system becomes equal to or higher than the set temperature TH1, and the determination in step 103 is affirmed. At this time, moisture condensed in the engine exhaust system has not evaporated, and the heater is operated in step 105. Of course, in starting at a time when the outside air temperature is high or restarting immediately after stopping the engine, the determination in step 103 is affirmed from the beginning, and the heater is immediately operated in step 105.
[0015]
Next, in step 106, it is determined whether or not 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 particulate adhering amount S to the oxygen sensor 8 is integrated and the process ends. Since the particulates adhering to the oxygen sensor 8 do not ignite and burn unless the temperature is equal to the activation temperature (650 ° C.) of the oxygen sensor 8, the oxygen sensor 8 is initially heated by the heater. Particulates in the exhaust gas are newly attached to 8.
[0016]
When this series of processing 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, oxidation of SOF adhering to the oxygen sensor 8 and combustion of particulates are started. At this time, even if the combustion air-fuel ratio control of the internal combustion engine by the oxygen sensor is started, 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 as the particulates burn around the oxygen sensor 8, so that the oxygen sensor 8 has a true air-fuel ratio of the exhaust gas. It is not always output that it is richer than the value and that it is leaner than the stoichiometric air-fuel ratio.
[0017]
In this flowchart, as soon as the determination in step 106 is affirmed, the control of the internal combustion engine by the oxygen sensor 8 is not started, but in step 107, the particulate adhering amount S to the oxygen sensor 8 accumulated so far is determined. The set amount b is decreased, and it is determined in step 108 whether the particulate adhesion amount S has become 0 or less. This set amount b is the amount of particulates burned on the oxygen sensor 8 at the execution interval of this flowchart.
[0018]
When the determination in step 108 is negative, particulates are attached to the oxygen sensor 8 and the particulates are being burned. At this time, the particulates in the exhaust gas are newly added to the oxygen sensor 8. 8 adheres. As a result, in step 104, the set amount a described above is added to the particulate adhesion amount S, and the processing ends. Of course, the amount of particulates burned out on the oxygen sensor per unit time is considerably larger than the amount of particulates newly adhering to the oxygen sensor 8, and if this series of processing is repeated, the judgment in step 108 is surely made. Affirmed.
[0019]
When the determination in step 108 is affirmed, in step 109, the combustion air-fuel ratio control of the internal combustion engine using the oxygen sensor 8 is started. Since the particulates on the oxygen sensor 8 are completely burned out at this time, the output of the oxygen sensor is accurate, and accurate combustion air-fuel ratio control using the oxygen sensor 8 becomes possible. Next, in step 110, the flag F described above is set to 1. Thereafter, since the determination in step 101 is affirmed, the processing of this flowchart described so far is not repeated unless the flag F is reset to 0 by the engine stop.
[0020]
After the heater operation control according to this flowchart, normal heater operation control is performed. This normal heater operation control is to maintain the oxygen sensor in the vicinity of the activation temperature by, for example, operating the heater when it is determined that the temperature of the exhaust gas has decreased based on the engine operating state. Thus, since the oxygen sensor 8 is maintained at the activation temperature, thereafter, the particulates adhering to the oxygen sensor 8 are immediately burned off. This momentary slight amount of particulate burnout hardly changes the oxygen concentration around the oxygen sensor 8.
[0021]
In the flowchart described above, the temperature TH of the engine exhaust system is detected and used to determine whether or not moisture is condensed in the engine exhaust system. However, this does not limit the present invention. The engine cooling water temperature is detected by the water temperature sensor 10 at the time of start-up, or the outside air temperature or the like is detected, and the temperature TH of the engine exhaust system is estimated based on the detected temperature and used, or the detected cooling The water temperature or the outside air temperature may be used directly. As described above, in the restart immediately after the engine is stopped, the temperature of the engine exhaust system is high, and condensation does not occur in the engine exhaust system. Thereby, when the difference between the engine coolant temperature detected at the time of starting the engine and the outside air temperature is equal to or higher than a predetermined temperature, it may be determined that the engine is restarted immediately after the engine is stopped and the heater may be operated immediately. In this flowchart, the temperature TH of the engine exhaust system is detected and used to determine whether or not the moisture condensed in the engine exhaust system has been evaporated. Based on the engine cooling water temperature or the outside air temperature, it may be determined whether or not moisture condensed in the engine exhaust system has been evaporated in consideration of the operating state immediately after engine startup, elapsed time, and the like. 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 startup is, the more affirmative this determination is. The elapsed time until is shortened. 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 has sufficiently increased and the condensed moisture has not evaporated.
[0022]
In this flowchart, the heater operating time until the oxygen sensor 8 reaches the activation temperature is set time t1, but if the determination in step 103 is affirmative from the beginning when the engine is started, the temperature of the engine exhaust system The higher the TH, the higher the temperature of the oxygen sensor itself from the beginning, so the set time t1 may be shortened.
[0023]
Further, in this flowchart, the particulate adhering amount S to the oxygen sensor at the time of starting the heater operation is the value before starting the combustion air-fuel ratio control by the oxygen sensor at the time of the previous engine start (determination of step 108). If the engine is stopped before the affirmative), the particulate adhesion amount S at this time is stored, so that the stored particulate adhesion amount S is the initial value at the time of engine startup this time. used. Thus, even in such a case, when the determination in step 108 is affirmative, no particulates are attached to the oxygen sensor 8.
[0024]
Thus, this flowchart estimates the amount of particulate adhering to the oxygen sensor at the time of starting the heater operation, and the larger the estimated amount of particulate adhering, the more until the oxygen sensor provides an accurate output. The operation time of the heater is determined to be long. Actually, in this flowchart, the amount of particulate adhering to the oxygen sensor at each time from the start of the engine to the start of the combustion air-fuel ratio control by the oxygen sensor is accurately grasped. However, since the time for burning out the particulate adhering to the oxygen sensor does not become so long, for example, the accumulation of the particulate adhesion amount S may be omitted while the heater is operated for the set time t1. That is, the determination may be terminated while the determination in step 106 is negative.
[0025]
In the estimation of the particulate adhesion amount, in step 104, the amount of particulate newly adhering at every execution interval of the flowchart is set as the set amount a, and this is integrated. This set amount a is based on the engine operating state. You may make it change in consideration of the difference in the particulate discharge amount discharged | emitted from a combustion chamber.
[0026]
In addition, if the amount of particulate adhering to the oxygen sensor at each time is not accurately grasped and the heater is not operated for a while after the engine is started, it is assumed that the particulate has adhered to the oxygen sensor. Even if the heating time of the heater until it provides an accurate output is simply increased by a predetermined time, the particulates can be burned out in this predetermined time, and good combustion air-fuel ratio control by the oxygen sensor can be realized It becomes.
[0027]
In this embodiment, as shown in the time chart of FIG. 3, the operation of the heater is stopped from time A when the engine start is completed, and the oxygen sensor is mechanically damaged due to moisture condensation in the engine exhaust system in the shortest time. And at the time B when this is realized, the heater is activated to activate the oxygen sensor and the particulates on the oxygen sensor are burned out. From the time C at which this is realized, the combustion air-fuel ratio is based on the accurate output of the oxygen sensor. Control is started. Compared to this, in the past, since particulate adhesion to the oxygen sensor is not taken into consideration, the output of the oxygen sensor is inaccurate at time C ′ when the oxygen sensor is activated by operating the heater from time B. Nevertheless, the combustion air-fuel ratio control by the oxygen sensor was started.
[0028]
In another prior art, as shown in the time chart of FIG. 4, for example, the control of the internal combustion engine that is determined in advance to start the combustion air-fuel ratio control by the oxygen sensor when the coolant temperature reaches a predetermined temperature, for example. In the apparatus, the combustion air-fuel ratio is activated so that the oxygen sensor is activated in accordance with the start of the combustion air-fuel ratio control (timing C) in order to secure the longest possible time to eliminate the moisture condensed in the engine exhaust system. The heater is started to operate (time B ′) earlier than the control start time by a time required 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 combustion air-fuel ratio control. Thus, the heater is started to operate earlier (time B) by a total time including the time required for burning out the particulates adhering to the oxygen sensor.
[0029]
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, when another sensor such as a pressure sensor exposed to exhaust gas is disposed in the engine exhaust system, this sensor activates itself. In order to prevent mechanical damage due to condensed moisture, etc., the heater is not operated for a while after starting the engine, and particulates adhere to this sensor. If the output of the sensor is obstructed, the heating time of the heater until the sensor provides an accurate output is determined in consideration of the particulate adhering 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 is not limited to a diesel engine, and may be any engine that includes particulates in the exhaust gas, such as a spark ignition internal combustion engine capable of stratified combustion.
[0030]
【The invention's effect】
An internal combustion engine control apparatus according to the present invention includes a sensor provided in an engine exhaust system through which exhaust gas containing particulates passes and a heater for heating the sensor, and operates the heater for a while after the engine is started. In a control device for an internal combustion engine that is not allowed to be controlled, the heating time of the heater until the sensor provides an accurate output is determined in consideration of particulate adhesion to the sensor at the time of starting the heater. Yes. While the heater is not in operation, particulates in the exhaust gas adhere to the sensor, and even if the sensor is activated until the particulates are burned out, accurate output cannot be provided. According to the engine control device, the heating time of the heater is determined in consideration of the adhesion of the particulates to the sensor. Therefore, the particulates can be burned out after this heating time, and accurate control by the sensor is possible. It is possible to achieve with certainty.
[Brief description of the drawings]
FIG. 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 heater operation control performed by the 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 for comparing the heater operation control in the control device according to the present invention with the conventional heater operation control.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine main body 2 ... Engine intake system 3 ... Engine exhaust system 8 ... Oxygen sensor 20 ... Control apparatus

Claims (2)

A control device for an internal combustion engine, comprising a sensor provided in an engine exhaust system through which exhaust gas containing particulates passes, and a heater for heating the sensor, so that the heater is not operated for a while after the engine is started In the control of an internal combustion engine, the heating time of the heater until the sensor provides an accurate output is determined in consideration of particulate adhering to the sensor at the time of starting the operation of the heater apparatus. 2. The particulate adhesion amount to the sensor at the time of starting the operation of the heater is estimated, and the heating time is increased as the estimated particulate adhesion amount increases. Control device for internal combustion engine.

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