JP2005002974A - Heater controller for exhaust gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heater controller for an exhaust gas sensor which controller controls the temperature of the exhaust gas sensor element at a target temperature irrespective of temperature variation around the sensor. <P>SOLUTION: The controller comprises air-fuel ratio sensors maintained at a predetermined activation temperature by a heater in the exhaust channel of an internal-combustion engine. When a fuel is injected into the internal-combustion engine (except during fuel cut operation), a basic target value R<SB>N</SB>is employed as the control target impedance (Step 102). When the fuel injection into the combustion engine is stopped (during fuel cut-off), a high temperature target value R<SB>FC</SB>set lower than the basic target value R<SB>N</SB>is employed as the control target impedance (Step 104). The heater is operated to make the impedance of the air-fuel ratio sensor element the above-mentioned control target impedance in each case (Step 106). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas sensor heater control device, and more particularly to a control device suitable for controlling an exhaust gas sensor heater disposed in an exhaust passage of an internal combustion engine.
[0002]
[Prior art]
Conventionally, as disclosed in, for example, Japanese Patent Laid-Open No. 4-148856, there is known a system including an air-fuel ratio sensor for detecting an exhaust air-fuel ratio in an exhaust passage of an internal combustion engine. The air-fuel ratio sensor includes a heater. The conventional apparatus calculates the element impedance of the air-fuel ratio sensor and controls the heater so that the element impedance is constant. According to such a configuration, the element temperature of the air-fuel ratio sensor can be maintained at a predetermined activation temperature.
[0003]
[Patent Document 1]
JP-A-4-148856 [Patent Document 2]
Japanese Patent Laid-Open No. 3-42564
[Problems to be solved by the invention]
A part of the air-fuel ratio sensor arranged in the exhaust passage is exposed to gas flowing through the exhaust passage. For this reason, even if the temperature is controlled by the heater, the element temperature of the air-fuel ratio sensor may deviate from the target temperature depending on the temperature of the gas flowing through the exhaust passage.
[0005]
That is, when a fuel cut (hereinafter referred to as “F / C”) is performed in the vehicle, gas that has not been subjected to combustion in the cylinder is discharged into the exhaust passage. In this case, since the element temperature of the air-fuel ratio sensor decreases due to cooling with the gas, the sensor output decreases. As a result, there is a situation in which the sensor output is not stable for a while until the element temperature returns from the F / C to a predetermined temperature.
[0006]
In an eco-run vehicle or a hybrid vehicle, the internal combustion engine may be stopped even when the vehicle system is operating. In this case, immediately after the internal combustion engine is restarted from the stopped state, the exhaust gas having a low temperature flows through the exhaust passage. For this reason, the element temperature decreases on the same principle as in F / C, and then the sensor output is not stable until the element temperature returns to a predetermined temperature.
[0007]
The above-mentioned conventional apparatus controls the element impedance to be a constant target value regardless of the operating state of the internal combustion engine, and the element temperature of the air-fuel ratio sensor at the time of F / C or at the restart of the internal combustion engine There was no consideration for changes.
[0008]
The present invention has been made to solve the above-described problems, and controls the heater of an exhaust gas sensor to control the element temperature of the exhaust gas sensor to a target temperature regardless of changes in the temperature environment surrounding the exhaust gas sensor. An object is to provide an apparatus.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a first invention is a heater control device for an exhaust gas sensor that controls a heater so that an element temperature of an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine becomes a predetermined activation temperature. ,
Heater driving means for driving the heater so that the element impedance of the exhaust gas sensor becomes a target impedance during operation of the vehicle system;
First impedance setting means for setting a first target impedance used during operation of the vehicle system and execution of fuel injection to the internal combustion engine;
Second impedance setting means for setting a second target impedance used during operation of the vehicle system and when fuel injection to the internal combustion engine is stopped to be lower than the first target impedance;
It is characterized by providing.
[0010]
The second invention is characterized in that, in the first invention, the second impedance setting means sets the second target impedance based on an intake air temperature.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.
[0012]
Embodiment 1 FIG.
FIG. 1 shows an internal combustion engine 10 equipped with a heater control apparatus according to Embodiment 1 of the present invention. An intake passage 12 and an exhaust passage 14 communicate with the internal combustion engine 10. A catalyst 16 is disposed in the exhaust passage 14. Air-fuel ratio sensors 18 and 20 are disposed upstream and downstream of the catalyst 16.
[0013]
The air-fuel ratio sensors 18 and 20 are sensors that emit an output corresponding to the oxygen concentration in the exhaust gas. The oxygen concentration in the exhaust gas has a correlation with the exhaust air-fuel ratio. Therefore, the air-fuel ratio sensors 18 and 20 can detect the air-fuel ratio of the exhaust gas upstream and downstream of the catalyst 16. An ECU (Electronic Control Unit) 30 is connected to the air-fuel ratio sensors 18 and 20.
[0014]
FIG. 2 is a circuit diagram equivalently showing the internal structure of the air-fuel ratio sensor 18 shown in FIG. The air-fuel ratio sensor 20 has the same structure as the air-fuel ratio sensor 18. Here, only the structure of the air-fuel ratio sensor 18 will be described as a representative example thereof. As shown in FIG. 2, the air-fuel ratio sensor 18 includes a sensor element 32. A heater 34 is incorporated in the air-fuel ratio sensor 18. The ECU 30 performs control for maintaining the element temperature of the air-fuel ratio sensor 18 at a predetermined activation temperature after the operation of the vehicle system is started (after the IG switch of the vehicle is turned on).
[0015]
In order for the air-fuel ratio sensor 18 to function normally, the sensor element 32 needs to be controlled to the above-described activation temperature. Since the temperature of the sensor element 32 has a correlation with the element impedance, the element temperature can be detected by calculating the element impedance. Therefore, the ECU 30 can control the temperature of the sensor element 32 to the target temperature by controlling the power supplied to the heater 34 so that the calculated value of the element impedance becomes the target value. More specifically, when the element impedance is lower than the target value, the ECU 30 can lower the element temperature by reducing the power supplied to the heater, and conversely, when the element impedance is higher than the target value. The element temperature can be increased by increasing the power supplied to the heater.
[0016]
Next, an outline of characteristic operations of the present embodiment will be described with reference to FIG.
FIG. 3 is a timing chart for explaining an operation in which the ECU 30 changes the target impedance during the F / C. Specifically, FIG. 3A shows an F / C period and a non-F / C period. FIG. 3B shows the target impedance of the sensor element 32 set according to the execution state of F / C. As shown in this figure, in this embodiment, a lower target impedance is set during F / C than during non-F / C. Hereinafter, the target impedance used during non-F / C is referred to as “basic target value R _N ”, and the target impedance used during F / C is referred to as “high temperature target value R _FC ”.
[0017]
FIG. 3C shows changes in the element temperature of the sensor element 32. The curve shown by a broken line in FIG. 3 (C), the shows the device temperature when the target impedance is maintained at all times to the basic target value R _N, while curve indicated by a solid line, in a non-F / C, the basic target value R _N is used as a target value, shown during F / C, the element temperature when the high temperature target value R _FC was used as a target value.
[0018]
During the fuel cut, a gas having a lower temperature than that during non-F / C is discharged to the exhaust passage 14. The air-fuel ratio sensor 18 is disposed so as to be exposed to the exhaust gas. For this reason, the amount of heat released from the sensor element 32 increases during F / C when the exhaust temperature decreases. Therefore, during F / C and non-F / C, when the heater is controlled while the target impedance is constant at the basic target value _RN , the temperature of the sensor element 32 tends to decrease. Under such circumstances, if the target impedance is set low (the target temperature is set high), a decrease in the element temperature can be avoided. Therefore, in the present embodiment, as described above, the target impedance is changed between F / C and non-F / C. According to such a configuration, as indicated by a solid line in FIG. 3C, the temperature of the sensor element 32 can be kept constant regardless of whether it is during F / C or non-F / C.
[0019]
Next, with reference to FIG. 4, the content of the process which ECU30 performs in this embodiment is demonstrated concretely.
FIG. 4 is a flowchart of a control routine executed by the ECU 30 shown in FIG. 1 to realize the above function. Note that the routine shown in FIG. 4 is always executed at predetermined intervals while the vehicle system is operating.
[0020]
In the routine shown in FIG. 4, it is first determined whether or not F / C is being performed (step 100).
As a result, when it is determined in step 100 that F / C is not being performed, it can be determined that high-temperature exhaust gas is being discharged into the exhaust passage 14. In this case, the basic target value _{R N} is used as the control target impedance (step 102). The basic target value _RN is a value set in advance by adaptation or the like as a target value for setting the temperature of the sensor element 32 to the activation temperature in a situation where fuel injection is being performed.
[0021]
Next, the element impedance of the sensor element 32 is calculated, and the heater is controlled so that the calculated value becomes the control target impedance (step 106). Here, in step 102, since the target impedance is the basic target value R _N, the processing of this step, the impedance of the sensor element 32 is a heater control is performed so that the basic target value R _N.
[0022]
On the other hand, when it is determined in step 100 that F / C is being performed, the high temperature target value R _FC is used as the control target impedance (step 104). The high temperature target value R _FC is a value set in advance by adaptation or the like as a target value for setting the temperature of the sensor element 32 to the activation temperature during F / C. Further, the high-temperature target value _{R FC satisfies} the relationship of _R FC <R _N.
[0023]
Next, the process of step 106 is executed. Here, since the target impedance is set to the high temperature target value R _FC in step 104, the heater control is performed by the processing of this step so that the impedance of the sensor element 32 becomes the high temperature target value R _FC .
[0024]
According to the processing of the above routine, the element temperature of the sensor element 32 can be kept constant even during F / C. As a result, the element temperature of the sensor element 32 is kept constant regardless of whether it is during F / C or non-F / C, so that the ECU 30 can always acquire a stable sensor output.
[0025]
Incidentally, in the first embodiment described above, although the high-temperature target value R _FC used in F / C a constant value, the present invention is not limited thereto. That is, the temperature of the sensor element 32 during F / C tends to decrease greatly as the intake air becomes colder. For this reason, the high temperature target value R _FC may be set based on the intake air temperature.
[0026]
In the first embodiment described above, the ECU 30 executes the process of step 106, so that the “heater driving means” in the first invention executes the process of step 102. The “first impedance setting means” in the present invention realizes the “second impedance setting means” in the first invention by executing the processing of step 104 described above. The "first target impedance" in the basic target value R _N is the first invention, the "second target impedance" in the high-temperature target value R _FC is the first aspect of the present invention, and corresponds respectively.
[0027]
Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. 5 and FIG. In the present embodiment, an example in which the present invention is applied to an eco-run vehicle (a vehicle having an idling stop function) and a hybrid (HV) vehicle is shown. The apparatus of the present embodiment can be realized by causing the ECU 30 to execute the routine shown in FIG. 6 using the configuration of the first embodiment.
[0028]
FIG. 5 is a timing chart for explaining an operation in which the ECU 30 changes the target impedance while the operation of the internal combustion engine is stopped. Specifically, FIG. 5A shows a stop period and an operation period of the internal combustion engine. FIG. 5B shows the timing for changing the target impedance of the sensor element 32. Further, FIG. 5C shows a change in the element temperature of the sensor element 32.
[0029]
In an eco-run vehicle or an HV vehicle, even when the vehicle system is operating (a state where the key switch of the vehicle is turned on), the fuel injection may be stopped and the internal combustion engine 10 may be stopped (hereinafter referred to as “the fuel injection”). Such an operation state is referred to as “internal combustion engine stop operation”). As shown in FIG. 5 (B), in this embodiment, during engine shutdown, low target impedance is used than the basic target value R _N used during operation of the internal combustion engine. Hereinafter, the target impedance is referred to as “high temperature target value R _STP ”.
[0030]
Curve indicated by a broken line in FIG. 5 (C) shows a change of the element temperature when the heater is driven remains constant unchanged the target impedance R _N even during engine stop operation. During the internal combustion engine stop operation, the sensor element 32 is exposed to the atmosphere. That is, in this case, the sensor element 32 is placed in a low temperature environment. However, since the atmosphere in the exhaust passage 14 does not flow during the internal combustion engine stop operation, the amount of heat released from the sensor element 32 is not significantly different from that during normal operation of the internal combustion engine. For this reason, even if the target impedance is constant, the temperature of the sensor element 32 does not drop significantly compared with the normal time during the stop operation of the internal combustion engine.
[0031]
Immediately after the internal combustion engine 10 is restarted from the stopped state, the exhaust gas having a low temperature flows through the exhaust passage 14. When a large amount of low-temperature exhaust gas flows, the amount of heat released from the sensor element 32 increases abruptly, and as shown by a broken line in FIG. Therefore, in the present embodiment, in anticipation of a decrease in the element temperature accompanying the restart of the internal combustion engine, the element temperature during the internal combustion engine stop operation is set higher than the normal element temperature in advance. And the target impedance is changed during operation of the internal combustion engine. According to such a configuration, as indicated by a solid line in FIG. 5C, it is effective that the temperature of the sensor element 32 greatly falls below the target temperature immediately after the internal combustion engine in a stopped state is restarted. It can be avoided.
[0032]
Next, with reference to FIG. 6, the content of the process which ECU30 performs in this embodiment is demonstrated concretely.
FIG. 6 is a flowchart of a control routine executed by the ECU 30 shown in FIG. 1 in order to realize the above function. Note that the routine shown in FIG. 6 is always executed at predetermined intervals while the vehicle system is operating.
[0033]
In the routine shown in FIG. 6, first, it is determined whether or not the internal combustion engine is stopped (step 108).
As a result, if it is determined in step 108 that the internal combustion engine is not stopped, it can be determined that high-temperature exhaust gas is being discharged into the exhaust passage 14. In this case, the basic target value _{R N} is used as the control target impedance (step 102).
[0034]
Next, the element impedance of the sensor element 32 is calculated, and the heater is controlled so that the calculated value becomes the control target impedance (step 106). Here, in step 102, since the target impedance is the basic target value R _N, the processing of this step, the impedance of the sensor element 32 is a heater control is performed so that the basic target value R _N.
[0035]
On the other hand, if it is determined in step 108 that the internal combustion engine is stopped, the high temperature target value _RSTP is used as the control target impedance (step 110). The high temperature target value _RSTP is a value set in advance as a target value for allowing the temperature of the sensor element 32 to converge to the target temperature after the internal combustion engine 10 is restarted. Further, the high-temperature target value _{R STP satisfies} the relationship of _R STP _{<R N.}
[0036]
Next, the process of step 106 is executed. Here, since the target impedance is set to the high temperature target value _RSTP in step 110, the heater control is performed by the processing in this step so that the impedance of the sensor element 32 becomes the high temperature target value _RSTP .
[0037]
According to the processing of the above routine, the temperature of the sensor element 32 during the internal combustion engine stop operation can be made higher than the target temperature during normal internal combustion engine operation. For this reason, even if the temperature of the sensor element 32 is lowered by the low-temperature exhaust gas flowing in large quantities after the internal combustion engine 10 is restarted, the element temperature can be controlled to the target temperature. For this reason, after the internal combustion engine 10 is restarted, the ECU 30 can acquire a stable sensor output.
[0038]
In the second embodiment described above, the timing for changing from the basic target value _RN to the high temperature target value _RSTP is set to be at the start of the internal combustion engine stop operation. It is not limited. That is, in the HV vehicle, it may be possible to predict the next restart of the internal combustion engine in advance. In this case, the temperature of the sensor element 32 during the internal combustion engine stop operation only needs to be high in advance so that the element temperature after the restart becomes a predetermined target temperature. That is, it is not always necessary to increase the element temperature over the entire area during the internal combustion engine stop operation. Therefore, when the restart time of the internal combustion engine can be predicted in advance, the timing for starting the change to the high temperature target value _RSTP may be set to a time point that is an appropriate period after the restart time of the internal combustion engine 10.
[0039]
In the second embodiment described above, the “second impedance setting means” according to the first aspect of the present invention is implemented when the ECU 30 executes the processing of step 110 described above. Further, the high temperature target value _RSTP corresponds to the “second target impedance” in the first invention.
[0040]
In the first and second embodiments described above, the control target of the ECU 30 is limited to an air-fuel ratio sensor (a sensor that generates an output corresponding to the oxygen concentration in the exhaust gas) provided with a heater. It is not limited to. That is, the present invention is not limited to an air-fuel ratio sensor provided with a heater, but may be applied to an oxygen sensor that emits an output according to whether the exhaust air-fuel ratio is rich or lean.
[0041]
【The invention's effect】
Since the present invention is configured as described above, the following effects can be obtained.
According to the first aspect, the target value of the element temperature of the exhaust gas sensor can be set to a target value suitable for the operating state of the vehicle system. Therefore, according to the present invention, the element temperature of the exhaust gas sensor can be controlled to the target temperature regardless of the change in the temperature environment surrounding the exhaust gas sensor.
[0042]
According to the second aspect of the invention, the second target impedance used while stopping fuel injection to the internal combustion engine can be appropriately changed based on the intake air temperature. Therefore, according to the present invention, the element temperature of the exhaust gas sensor can be more accurately controlled to the target temperature without being affected by the intake air temperature during and immediately after the recovery from the F / C. .
[Brief description of the drawings]
FIG. 1 is a diagram showing an internal combustion engine equipped with a heater control apparatus according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram equivalently showing the internal structure of the air-fuel ratio sensor shown in FIG.
FIG. 3 is a timing chart for explaining an operation in which the ECU shown in FIG. 1 changes a target impedance during F / C.
FIG. 4 is a flowchart of a control routine executed in Embodiment 1 of the present invention.
FIG. 5 is a timing chart for explaining an operation in which the ECU shown in FIG. 1 changes a target impedance during an internal combustion engine stop operation;
FIG. 6 is a flowchart of a control routine executed in the second embodiment of the present invention.
[Explanation of symbols]
10 Internal combustion engine 14 Exhaust passage 18, 20 Air-fuel ratio sensor 30 ECU
32 Sensor element 34 Heater

Claims (2)

An exhaust gas sensor heater control device for controlling a heater so that an element temperature of an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine becomes a predetermined activation temperature,
Heater driving means for driving the heater so that the element impedance of the exhaust gas sensor becomes a target impedance during operation of the vehicle system;
First impedance setting means for setting a first target impedance used during operation of the vehicle system and execution of fuel injection to the internal combustion engine;
Second impedance setting means for setting a second target impedance used during operation of the vehicle system and when fuel injection to the internal combustion engine is stopped to be lower than the first target impedance;
A heater control device for an exhaust gas sensor. The exhaust gas sensor heater control device according to claim 1, wherein the second impedance setting means sets the second target impedance based on an intake air temperature.

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