JP2001050929A - Detection apparatus for concentration of oxygen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire the relationship between the temperature of a heater and the resistance value of the heater, in a short time without installing a separate routine. SOLUTION: An air/fuel ratio sensor 101, which is installed in the exhaust passage 6 of an engine 200, is provided. A heater 104 which heats the air/fuel ratio sensor is provided. A heater control means 100 which controls electric power supplied to the heater is provided. On the basis of the resistance value of the heater acquired in the specific operating state of the engine during the control of the electric power supplied to the heater by the feedback of the element impedance of the air-fuel ratio sensor performed after the activation of the air-fuel ratio sensor, the relationship between the temperature of the heater and the resistance value of the heater is acquired. When the relationship between the element temperature and the element impedance of the air-fuel ratio sensor is different from the same relationship at a time when the air-fuel ratio sensor is an initial product, the acquisition of the relationship between the temperature of the heater and the resistance value of the heater is inhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration detecting apparatus, and more particularly, to a method of detecting a heater resistance value before an air-fuel ratio sensor for detecting an exhaust air-fuel ratio of an internal combustion engine (hereinafter referred to as an engine) is activated. After the activation of the air-fuel ratio sensor, the element impedance of the air-fuel ratio sensor is fed back to the heater so as to maintain the element temperature of the air-fuel ratio sensor at the activation temperature. The present invention relates to an oxygen concentration detection device that controls electric power.

[0002]

2. Description of the Related Art In recent years, in an air-fuel ratio control of an engine, an air-fuel ratio sensor and a catalyst are disposed in an exhaust system of the engine, and harmful components (HC, CO, NOx, etc.) in exhaust gas are maximized by the catalyst. For purification, feedback control is performed so that the exhaust air-fuel ratio of the engine detected by the air-fuel ratio sensor becomes a target air-fuel ratio, for example, a stoichiometric air-fuel ratio. As this air-fuel ratio sensor, a limiting current type oxygen concentration detecting element (oxygen sensor) that outputs a limiting current in proportion to the oxygen concentration contained in exhaust gas discharged from the engine is used. The limiting current type oxygen concentration detecting element detects the exhaust air-fuel ratio of the engine in a wide range and linearly from the oxygen concentration, and improves the air-fuel ratio control accuracy, and rich or stoichiometric air-fuel ratio (stoichiometric).
This is useful for controlling the engine exhaust air-fuel ratio to be the target air-fuel ratio between the lean wide-area air-fuel ratios.

[0003] It is essential that the oxygen concentration detecting element is kept in an active state in order to maintain the detection accuracy of the air-fuel ratio. Usually, the oxygen concentration detecting element is energized by turning on a heater attached to the element from the start of the engine. Heating control is performed on the heater so that the element is heated and activated early to maintain the active state. The heater control device for an oxygen concentration detection sensor disclosed in Japanese Patent Application Laid-Open No. 4-248454 variably controls the power supplied to the heater so that the resistance value of the heater installed in the oxygen concentration detection sensor becomes a target resistance value. is there.

A heater control device for an oxygen sensor disclosed in Japanese Patent Application Laid-Open No. 8-278279 supplies all electric power to the heater until the heater temperature reaches a predetermined temperature for early activation of the sensor element at the beginning of energization of the heater. When the heater temperature reaches a predetermined temperature, power corresponding to the heater temperature is supplied to the heater, and when the temperature of the sensor element reaches the predetermined temperature, power corresponding to the element temperature of the oxygen sensor is supplied to the heater. The temperature of the sensor element is estimated from the element impedance value.

[0005]

However, in the heater control device for an oxygen concentration detecting sensor disclosed in Japanese Patent Application Laid-Open No. 4-248454, the method disclosed in Japanese Patent Application Laid-Open No. 8-27827 is disclosed.
In the case of controlling the power supply to the heater by feeding back the element impedance of the air-fuel ratio sensor to a target value as disclosed in Japanese Patent Application Laid-Open No. 9-209, for example, in order to prevent the heater from reaching a temperature limit, It is necessary to set the upper limit value of the heater resistance value and monitor the heater resistance value so that the heater resistance value does not exceed the heater resistance upper limit value, but if the relationship between the heater temperature and the heater resistance value is not obtained correctly However, it is necessary to execute another routine based on the heater supply power in order to acquire this relationship, and it takes a long time to acquire the relationship between the heater temperature and the heater resistance value.

In the above case, the relationship between the element temperature and the element impedance of the air-fuel ratio sensor is an initial product such as when the exhaust temperature of the engine is low or when the air-fuel ratio sensor changes over time. When the relationship is different from the above, the element temperature and the element impedance change and become unstable, and the heater resistance becomes unstable, so that the relation between the heater temperature and the heater resistance is erroneously obtained. There is.

Therefore, the present invention solves the above-mentioned problem and eliminates the need for providing another routine for obtaining the relationship between the heater temperature and the heater resistance value. The main object of the present invention is to provide an oxygen concentration detection device capable of acquiring the relationship with the oxygen concentration detection device. Another object of the present invention is to prevent erroneous acquisition of the relationship between the heater temperature and the heater resistance when the relationship between the element temperature and the element impedance is broken.

[0008]

An oxygen concentration detecting apparatus according to the present invention for solving the above-mentioned problems includes an air-fuel ratio sensor provided in an exhaust passage of an internal combustion engine, a heater for heating the air-fuel ratio sensor, and a heater. And heater control means for controlling the supplied electric power.In the oxygen concentration detection device, the air-fuel ratio sensor is activated after the activation of the air-fuel ratio sensor. Acquiring a relationship between the temperature of the heater and the resistance value of the heater based on the resistance value of the heater acquired in a specific operation state of the internal combustion engine during control of the power supplied to the heater; It is characterized by.

With the above configuration, the relationship between the heater temperature and the heater resistance can be acquired in a short time without providing another routine for acquiring the relationship between the heater temperature and the heater resistance. In the above oxygen concentration detection device, when the relationship between the element temperature and the element impedance of the air-fuel ratio sensor is different from the same relationship when the air-fuel ratio sensor is an initial product, the relationship between the heater temperature and the resistance value of the heater Prohibit the acquisition of

With the above configuration, it is possible to avoid erroneous acquisition of the relationship between the heater temperature and the heater resistance value when the heater resistance value is unstable, such as aging of the air-fuel ratio sensor.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of an embodiment of an internal combustion engine provided with the oxygen concentration detecting device according to the present invention. In FIG. In FIG. 1, reference numeral 1 denotes a cylinder block, 2 denotes a piston, 3 denotes a cylinder head, 4 denotes a combustion chamber, 5 denotes an intake manifold, and 6 denotes an exhaust manifold. The intake manifold 5 is connected to an air cleaner 10 via a surge tank 7, an intake duct 8, and an air flow meter 9. A throttle valve 11 is disposed in the intake duct 8,
In the intake manifold 5, a fuel injection valve 12 is provided with an intake port 13.
It is arranged toward. The exhaust manifold 6 has an exhaust pipe 14.
And HC, CO, N
A catalytic converter 15 having a three-way catalyst that simultaneously purifies three components of Ox and has an oxygen storage effect is provided.

An electronic control unit (ECU) 100 is composed of a digital computer, and is connected to a ROM 42, a RAM 43 and a backup B.R. RAM 44, CPU 45, input port 46
And an output port 47, and the like. The air flow meter 9 generates an output voltage proportional to the amount of intake air, and outputs the output voltage signal to the input port 4 via the A / D converter 48.
Enter 6 An air-fuel ratio sensor 101 is disposed on the upstream side in the exhaust manifold 6, and the air-fuel ratio sensor 101 detects the oxygen concentration in the exhaust gas, and outputs the output signal to the air-fuel ratio sensor circuit 103 and the A / D converter 48. Input port 46 through
To enter.

The opening of the throttle valve 11 in the intake duct 8 is changed in conjunction with the depression of an accelerator pedal (not shown). The throttle valve 11 is provided with a throttle position sensor 18 having an idle switch for detecting a fully closed state of the throttle opening. The throttle position sensor 18 is connected to the ECU 100 and connected to the ECU 1.
In addition to inputting an on / off signal XIDLE of the idle switch to the input port 46 of 00, an analog voltage signal proportional to the throttle opening is input to the input port 46 via the A / D converter 48.

The surge tank 7 is provided with a pressure sensor 19 for detecting an absolute pressure in the intake passage. The pressure sensor 19 outputs an analog voltage signal proportional to the intake pressure to the A / D converter 4.
8 to the input port 46. A water temperature sensor 20 for detecting a cooling water temperature of the engine 200 in the water jacket is attached to the cylinder block 1. The water temperature sensor 20 outputs an analog voltage signal proportional to the cooling water temperature of the engine 200 to the A / D converter 48. And input to the input port 46 via the interface.

The voltage of the battery 105 is also connected to the ECU 100, and the voltage of the battery 105
The data is input to the input port 46 via the D converter 48. A vehicle speed sensor 21 for detecting the speed of the vehicle on which the engine 200 is mounted is also connected to the ECU 100.
Is input to the input port 46 via the A / D converter 48 in the ECU 100.

The distributor 16 is provided with two crank angle sensors 33 and 34.
Reference numeral 3 denotes a crank angle sensor which converts a crank angle into a reference position at every 720 ° CA and generates an output pulse signal.
Numeral 4 detects the position at every 30 ° CA in terms of the crank angle and generates an output pulse signal. These output pulse signals are input to the input port 46, and the output pulse signal of the crank angle sensor 34 is also input to the interrupt terminal of the CPU 45. From the output pulse signals of the crank angle sensors 33 and 34, for example, the rotation speed of the engine 200 is calculated.

On the other hand, the output port 47 is connected to the fuel injection valve 12 via a drive circuit 49. The amount of fuel injected into the intake passage 17 from the fuel injection valve 12 toward the intake port 13 is determined by the fuel that is opened by the drive circuit 49 so that the air-fuel ratio becomes the target air-fuel ratio, in this embodiment, the stoichiometric air-fuel ratio. It is controlled by varying the valve opening time of the injection valve 12.
The output port 47 is also connected to the alarm 22 via the drive circuit 49, and the alarm 22 is activated when it is determined that the air-fuel ratio sensor element 102 and the heater 104 have deteriorated.

The interruption of the CPU 45 occurs when the A / D conversion by the A / D converter is completed or when the output pulse signal of the crank angle sensor 34 is received. The digital data input to the input port 46 via the A / D converter 48 is
It is read every D conversion and stored in the RAM 43. Institution 2
The rotation number NE of 00 is also calculated and stored in the RAM 43 every time the output pulse signal of the crank angle sensor 34 is input to the interrupt terminal of the CPU 45. That is, the data of the engine 200 stored in the RAM 43 is constantly updated.

The heater 104 is connected to the air-fuel ratio sensor 101.
The digital data calculated by the CPU 45 by a process described later is output from the D / D converter through the output port 47.
The A converter 50 converts the voltage into an analog voltage, and the heater circuit 106
Is supplied to the heater 104 via the. FIG. 2 shows FIG.
FIG. 4 is a diagram showing control of an air-fuel ratio sensor 101 and a heater 104 shown in FIG. The air-fuel ratio sensor 101 for detecting the exhaust air-fuel ratio of the engine 200 shown in FIG. 1 includes an air-fuel ratio sensor element (hereinafter, referred to as a sensor element) 102 and a heater 104. Air-fuel ratio sensor circuit (hereinafter referred to as sensor circuit) 10
3 is provided in the ECU 100 and applies a voltage to the sensor element 102. The sensor circuit 103 receives an analog application voltage from the control unit A / FCU 110 which controls the air-fuel ratio sensor 1 in the ECU 100 composed of a digital computer, that is, the air-fuel ratio sensor control unit A / FCU 110, and outputs a voltage corresponding to the analog application voltage to the sensor element 102. Is applied. A
The / FCU 110 converts the digital data calculated according to the processing described later into an analog voltage by the D / A converter 50 provided therein and outputs the analog voltage to the sensor circuit 103.
With the application of this voltage, the A / FCU 110 detects a current flowing through the sensor element 102 that changes in proportion to the oxygen concentration in the gas to be detected, that is, the exhaust gas. A / FCU
110 is an A / A provided inside to detect this current.
The sensor element 1 is converted from the sensor circuit 103 by the D converter 48.
02 receives an analog voltage corresponding to the current flowing through the second circuit. A
The / FCU 110 converts this analog voltage into digital data, and uses the converted digital data for processing described later.

The output of the air-fuel ratio sensor 101 cannot be used for air-fuel ratio control unless the sensor element 102 is activated. For this reason, the A / FCU 110 supplies power from the battery 105 to the heater
4, the sensor element 102 is activated early, and after the sensor element 102 is activated, power is supplied to the heater 104 so as to maintain the active state. The air-fuel ratio sensor circuit 103 has an integration circuit therein, and the A / FC
A voltage obtained by converting a rectangular pulse input from the U 110 to the air-fuel ratio sensor circuit 103 into a sine-wave pulse is applied to the sensor element 102. This prevents detection error of the output current of the sensor element due to high frequency noise.

FIG. 3 is a diagram showing a correlation between the temperature and the impedance of the oxygen concentration detecting element. The relationship between the temperature and the impedance of the oxygen concentration detecting element (hereinafter simply referred to as the element) has a correlation as shown by the thick line in FIG. 3, that is, the relation that the impedance of the element decreases as the element temperature increases. is there. Focusing on this relationship, in the above-described heater energization control, the element temperature is derived by detecting the element impedance, and feedback control is performed so that the element temperature becomes a desired activation temperature, for example, 700 ° C. Is going. For example, as shown by the thick line in FIG.
The element impedance Zac is 700 ° for the initial control element temperature.
When the impedance of the element corresponding to C is 30Ω or more (Z
ac ≧ 30), that is, when the element temperature is 700 ° C. or less,
When the heater is energized and Zac is smaller than 30Ω (Zac <3
0), that is, when the element temperature exceeds 700 ° C., by performing control to cancel the energization of the heater, the element temperature is maintained at an activation temperature of 700 ° C. or higher, and the active state of the element is maintained. When the heater is energized, the amount of energization required to eliminate the deviation (Zac-30) between the impedance of the element and its target value is determined, and duty control is performed to supply the amount of energization.

As shown in FIG. 3, attention is paid to the fact that the resistance of the sensor element 102 depends on the temperature of the sensor element 102, that is, the resistance of the sensor element 102 decreases as the sensor element temperature increases.
The temperature of the sensor element 102 is maintained at a target temperature, for example, 700 ° C. by supplying power to the heater 104 so that the resistance of the sensor element 102 becomes a resistance value corresponding to the temperature at which the sensor element 102 maintains the active state, for example, 30Ω. Control is performed. The A / FCU 110 receives an analog voltage corresponding to the voltage and current of the heater 104 from the heater circuit 106 by an A / D converter 48 provided therein, converts the analog voltage into digital data, and uses the digital data for processing described later. I do. For example, a resistance value of the heater 104 is calculated, and based on the resistance value, electric power is supplied to the heater 104 in accordance with an operation state of the engine, and the temperature of the heater 104 is controlled so as to prevent the heater 104 from overheating (OT). Do.

FIG. 4 is a time chart of the heater control. In FIG. 4, the horizontal axis represents time, the vertical axis represents the duty ratio of the power supplied to the heater, the middle level represents the heater temperature, and the lower level represents the element impedance. With the start of the engine, the entire energization control with a duty ratio of 100% is performed from time t0 when energization of the heater is started to time t1 until the heater reaches a target (upper limit) temperature, for example, 1200 ° C. The temperature at which the sensor element is activated from t1 7
Until time t2 when the impedance reaches 30 Ω corresponding to 00 ° C, the heater temperature feedback control for maintaining the heater temperature at the target temperature is performed, and after time t2, the temperature of the sensor element is maintained at the element activation temperature of 700 ° C. Element temperature feedback control is performed. This heater control routine will be described below based on a flowchart.

FIG. 5 is a flowchart of a heater control routine. This routine has a predetermined period, for example, 100 ms.
Executed every ec. First, in step 501, it is determined whether an ignition switch (not shown) is ON or OFF, and if the ignition switch is ON, step 5 is executed.
The routine proceeds to step 02, and when the ignition switch is OFF, this routine ends. In step 502, the heater resistance RH is calculated from the voltage applied to the heater and the current supplied to the heater. In step 503, the heater resistance RH calculated in step 502 is compared with the heater resistance learning value RHG, and if RH ≧ RHG, the process proceeds to step 504, where RH
If <RHG, the process proceeds to step 505. Here, the heater resistance learning value RHG means that the heater temperature is the target temperature (120
The resistance value at the time of 0 ° C) is a value learned so as to be able to eliminate the variation due to each product or a change with time, and the heater full energization target heater resistance learning value stored in the backup RAM in step 1008 of FIG. HTRLMT. In addition, even if the heater resistance is kept at the target resistance value in consideration of the temperature limit of the heater (until the air-fuel ratio sensor is activated) in consideration of the heater temperature limit, the heater resistance learning value is calculated based on the heater life. The resistance value determined to have little effect on the resistance is learned as the target resistance value.

In step 504, the element impedance Zac is read. In step 506, the read Zac is compared with 30Ω corresponding to the activation temperature of the sensor element, and Zac>
If it is 30, it is determined that the sensor element is in the active state, and the process proceeds to step 508. If Zac ≦ 30, it is determined that the sensor element is in the inactive state, and the process proceeds to step 507. In step 505, full energization (100% duty) control is performed, in step 507, heater temperature feedback control is performed, and in step 508, element temperature feedback control is performed.

In the heater control shown in FIGS. 4 and 5, the overheating of the heater and the sensor element (Over Tempe) is performed.
In order to prevent the occurrence of the characteristic, the air-fuel ratio impedance Zac for the specific frequency of 5 KHz exceeds a predetermined value, for example, 5Ω from the element temperature control target value Zactg after the deterioration correction (Z
ac ≦ Zactg-5 (Ω)), and the result of the determination is YE
If S, it is determined that the temperature is normal, that is, the heater and the sensor element are not overheated, and the heater control routine shown in the flowchart of FIG. 5 is executed. Then, it is determined that the temperature of the sensor element is excessively high, and a process of setting DUTY (i) = 0 is performed.

Next, a description will be given of a routine for correcting element deterioration at the time of engine idling and a heater resistance learning routine for calculating a heater resistance learning value. FIG. 6 is a first half flowchart of the element deterioration correction and heater resistance learning routine during engine idling, and FIG. 7 is a second half flowchart of the routine. This routine is executed at a predetermined cycle, for example, every 128 msec. First, in step 601, the current HTWi, which is the current flowing through the heater resistor, the voltage HTVi applied to the heater resistor, and the duty ratio DUTYi of the heater power supply are read and the heater HTW is supplied to the heater.
i (= HTIi × HTVi × DUTYi) is calculated.

In step 602, it is determined whether or not a learning condition at the time of engine idling is satisfied. If the result of the determination is YES, the process proceeds to step 603, and if the result of the determination is NO, the present routine is terminated. . The learning condition when the engine is idle is considered to be satisfied when the following conditions indicating that the engine is in a fully warm-up steady idling state are satisfied. The engine-starting water temperature THWst is within a predetermined temperature range (THW1
≤ THWst ≤ THW2)-The battery voltage BAT is equal to or higher than a predetermined value KBAT (KBAT).
≤ BAT)-The impedance Zac (Ω) of the air-fuel ratio sensor is within a predetermined value range (KZac1 ≤ Zac ≤ KZac2)-The engine speed NE (rpm) is equal to or less than a predetermined value (NE ≤ KN)
E) ・ The engine intake pressure PM (mmHg) is equal to or less than a predetermined value (PM ≦ KP
M) ・ The vehicle speed SPD (km / h) is equal to or less than a predetermined value (SPD ≦ KSP)
D) The engine idle switch is turned on In step 603, it is determined whether or not a predetermined time has elapsed after the learning condition is satisfied. If the result of the determination is YES, the process proceeds to step 604. If the result of the determination is NO, the process proceeds to step 604. End the routine. In step 604, the learning condition satisfaction flag (XZACG) is turned on.

In step 605, it is determined whether the learning condition satisfaction flag (XZACG) is on or off in the previous processing cycle. When it is off (XZACG = 0), the process proceeds to step 606, and when it is on (XZACG = 1), step 607. Proceed to. In step 606, the integrated power amount ΣHTWi is cleared to 0, the integrated heater resistance value ΣHTri is cleared to 0, and the learning area elapsed time counter CZACGT is cleared to 0.

In step 607, the elapsed time counter CZACGT in the learning area is incremented (CZACGT
= CZACGT + 1). In step 608, the integrated power amount ΣHTWi in the current processing cycle is calculated from the following equation. ΣHTWi = ΣHTWi-1 + HTWi Here, ΣHTWi-1 indicates the integrated power amount of the previous processing cycle, and is cleared to 0 immediately after the ignition switch is turned on and the engine is started.

In step 609, the integrated heater resistance value Σ
HTRi is calculated from the following equation. ΣHTri = ΣHTri-1 + HTri Here, ΣHTri-1 indicates the heater resistance value in the previous processing cycle, and is cleared to 0 immediately after the ignition switch is turned on and the engine is started. In step 610,
The elapsed time counter CZACGT in the learning area is set to a predetermined value KZ.
It is determined whether or not ACGT or more (CZACGT ≧ KZACGT). If the determination result is YES, step 611 is executed.
If the result of the determination is NO, step 7 in FIG.
Go to 01. In step 611, the learning completion flag (XZAC
GE) on. After execution of step 611, the process proceeds to step 701 of the flowchart shown in FIG.

At step 701 in FIG. 7, it is determined whether the learning completion flag (XZACGE) is on or off. When the learning completion flag is on (XZACGE = 1), the process proceeds to step 702.
When the learning completion flag is off (XZACGE = 0), this routine ends. In step 702, a failure determination of the air-fuel ratio sensor is performed. That is, the integrated power amount of the current processing cycleΣ
It is determined whether HTWi is equal to or greater than a predetermined value K 値 HTW (ＷH
TWi ≧ KΣHTW) If the result of the determination is YES, it is determined that the air-fuel ratio sensor has failed, and the routine proceeds to step 703. If the result of the determination is NO, the routine proceeds to step 704. In step 703, a failure flag (XA
FSF) is set to ON, and this routine ends.

In step 704, a routine for calculating the element temperature control target learning value Zactgg from the heater integrated power amount ΣHTWi described later with reference to FIG. 8 is executed. Step 7
At 05, a heater resistance learning value HTRG is calculated from the integrated heater resistance value ΣHTri (FIG. 10). In step 706, the learning completion flag (XZACGE) is cleared to off. Next, the processing of step 704 in FIG. 7, that is, the routine for calculating the element temperature control target value from the integrated heater power will be described.

FIG. 8 is a flowchart of an element temperature control target learning value calculation routine. This routine has a predetermined cycle,
For example, it is executed every 128 msec. First, step 80
In step 1, the average power amount HTWAV is calculated from the following equation based on the integrated power amount of the heater ΣHTWi. In step 802, the correction amount ZACOT of the element temperature control target learning value Zactgg for estimating the deterioration of the sensor element from the average power amount HTWAV (watt · h) using the map shown in FIG.
(Ω) is calculated. In step 803, the target temperature learning value Zactggi for the current processing cycle is calculated from the following equation.

Zactggi = Zactggi-1 + ZACOT Here, Zactggi-1 is the element temperature control target learning value in the previous processing cycle. In step 804, the element temperature control target learning value Zactggi learned as described above is updated and stored in the battery backup SRAM as in the following equation. Zactggb = Zactggi FIG. 9 is a map for calculating the correction amount of the element temperature control target learning value from the heater average power amount. As can be seen from the map of FIG. 9, the correction amount ZACOT is set to a larger value as the average power amount HTWAV increases. This is because, with the deterioration of the air-fuel ratio sensor, the impedance characteristic of the sensor element changes, and control for raising the temperature of the sensor element, that is, control for lowering the element temperature control target learning value Zactggi, is performed. The amount of power to be supplied is large. The present invention
Therefore, by calculating the average amount of power supplied to the heater and controlling the element impedance to increase when the calculated average amount of power increases, it is possible to prevent overheating of the sensor element and the heater resistance. I have. Further, by preventing overheating of the sensor element and the heater resistor, it is possible to prevent early deterioration of the sensor element and the heater resistor and extend the life. Next, the processing of step 705 in FIG. 7, that is, the routine for calculating the heater resistance learning value from the integrated heater resistance value will be described below.

FIG. 10 is a flowchart of a heater resistance learning value calculation routine. In step 1001, it is determined whether or not the average electric power amount HTWAV of the heater based on the element impedance feedback of the air-fuel ratio sensor is within a predetermined range. The average power amount HTWAV of the heater uses the value calculated in step 801 of FIG. Whether the HTWAV is within the predetermined range is determined by determining whether the HTWAV when the engine exhaust temperature is stabilized, for example, when the learning condition at the time of engine idling is satisfied, is determined by the heater at the time of the initial product of the air-fuel ratio sensor. Heater supply power amount HTW corresponding to control temperature
Is determined based on whether or not the wattage is within the range. When the above determination result is YES, that is, when a specific operating state of the engine, for example, a learning condition at the time of engine idling is satisfied, the exhaust temperature of the engine is estimated to be stable. Stable without. Therefore, since it is determined that the heater resistance is also stable, step 10
In steps 1002 to 1008, an update process of the heater resistance learning value HTRG and the total energization target heater resistance learning value HTRLMT is executed. On the other hand, when the determination result is NO, that is, when the learning condition at the time of engine idling is not satisfied, the exhaust temperature of the engine is estimated to be unstable, so that the element impedance and the element temperature change and become unstable. Therefore, since it is determined that the heater resistance is also unstable, the routine ends without executing the update processing of the heater resistance learning value HTRG and the full energization target heater resistance learning value HTRLMT.

In step 1002, step 6 in FIG.
Heater integrated resistance value up to the current processing cycle calculated in 06Σ
From HTR _i and the number of integrations, the average resistance value HTRA of the heater
V is calculated from the following equation. In HTRAV = ΣHTR _i / integration count step 1003, when the learning condition is satisfied, that is, by calculating moderation heater resistance learning value HTRG _i at the time of engine idling is calculated from the following equation.

HTRG _i = (HTRG _i−1 × 31 + HT)
RAV) / 32 This heater resistance learning value HTRG _i is used as the heater temperature upper limit guard value during the element temperature feedback control in step 508 in FIG. 5 after the air-fuel ratio sensor is warmed up, that is, used as the RHG in step 503 in FIG. Is done. In other words, when the engine is idling, the temperature of the exhaust gas stabilizes at a low temperature, so the power supplied to the heater is constant and the heater stabilizes at a high temperature. Therefore, the heater resistance at this time is set to the upper limit guard value to prevent overheating of the heater. To prevent disconnection of the heater.

In step 1004, a heater full energization target heater resistance value HTR 1200 at the time of starting the engine is calculated from the following equation. HTR1200 = HTRG × k where k is a temperature coefficient. The heater resistance value HTR1 corresponding to 1200 ° C, which is a control target when the air-fuel ratio sensor is warmed up with respect to the heater temperature under the learning condition in which the heater resistance learning value HTRG is calculated by the above equation, for example, 850 ° C.
200 is required. In this case, the temperature coefficient k is k = H
TR1200 / HTR850.

In step 1005, it is determined whether or not the HTR 1200 is equal to or less than a predetermined value KHTR1200GD.
Step 1 when R1200 ≦ KHTR1200GD
Go to 006, HTR1200> KHTR1200GD
If so, the process proceeds to step 1007. At step 1006, the heater full energization target heater resistance learning value H at the time of starting the engine is set.
TRLMT is calculated from the following equation.

HTRLMT = HTR1200 In step 1007, a predetermined value KHTR12 is added to the heater full energization target heater resistance learning value HTRLMT as shown in the following equation.
Set 00GD and guard the upper limit. In HTRLMT = KHTR1200GD step 1008, stores the heater resistance learning value HTRG _i and heater full energization target heater resistance learning value HTRLMT the backup RAM.

The heater resistance learning value HTRG _i is used as an upper limit heater temperature guard value after the air-fuel ratio sensor is warmed up.
T is used as an upper limit heater temperature guard value during warm-up of the air-fuel ratio sensor. In the embodiment of the present invention described above with reference to the drawings, as the acquisition of the relationship between the heater temperature and the heater resistance value, the control of the power supply to the heater by the heater resistance feedback performed before the activation of the air-fuel ratio sensor is performed. Although the acquisition of the heater resistance learning value as the target resistance value of the heater has been described as an example, the present invention is not limited to this.

To obtain the relationship between the temperature of the heater and the resistance value of the heater: If the heater temperature is at a certain temperature (eg, 850 ° C., 1200
1), and obtain the heater resistance value at the time of When the heater is at the temperature limit (a state where abnormalities such as disconnection occur when the temperature is increased by supplying more power, or a state where it is not desirable to supply more power considering the life of the heater) Obtaining a heater resistance value;
Or, 3. Acquiring the upper limit guard value of the heater resistance value during the element impedance feedback control of the air-fuel ratio sensor.

In the above 3, even if the heater resistance continues to be at the target resistance value, the resistance value determined to have little effect on the heater life is set as the target resistance value as the upper limit guard value. You. As another embodiment of the present invention, for example, (1) in a device for estimating the sensor element temperature based on the sensor element impedance and controlling the heater supply power even before the air-fuel ratio sensor is activated, the heater resistance feedback control is performed. Without the heater resistance value
Guarding so as not to exceed a resistance value corresponding to a predetermined temperature, for example, 1200 ° C .; and (2) heater resistance learning without using a heater resistance learning value for an upper limit heater resistance value before activation of the air-fuel ratio sensor. A configuration is conceivable in which the value is used only as the upper limit heater resistance value during normal element impedance feedback control of the air-fuel ratio sensor.

[0045]

As described above, according to the oxygen concentration detecting device of the present invention, the above relationship can be obtained in a short time without providing another routine for acquiring the relationship between the heater temperature and the heater resistance value. Can be obtained. Further, according to the oxygen concentration detection device of the present invention, when the relationship between the element temperature and the element impedance of the air-fuel ratio sensor is different from the same relationship when the air-fuel ratio sensor is an initial product, the relationship between the heater temperature and the heater resistance value Therefore, it is possible to avoid erroneous acquisition of the relationship between the heater temperature and the heater resistance value when the heater resistance value is unstable such that the air-fuel ratio sensor changes over time.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an internal combustion engine including an oxygen concentration detection device according to the present invention.

FIG. 2 is a diagram showing control of an air-fuel ratio sensor and a heater shown in FIG.

FIG. 3 is a diagram showing a correlation between temperature and impedance of an oxygen concentration detecting element.

FIG. 4 is a time chart of heater control.

FIG. 5 is a flowchart of a heater control routine.

FIG. 6 is a first half flowchart of an element deterioration correction and heater resistance learning routine during engine idling.

FIG. 7 is a flowchart of the latter half of an element deterioration correction and heater resistance learning routine during engine idling.

FIG. 8 is a flowchart of an element temperature control target learning value calculation calculation routine.

FIG. 9 is a map for calculating a correction amount of an element temperature control target learning value from a heater average power amount.

FIG. 10 is a flowchart of a heater resistance learning value calculation routine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cylinder block 9 ... Air flow meter 18 ... Throttle position sensor 19 ... Intake pressure sensor 20 ... Water temperature sensor 21 ... Vehicle speed sensor 33, 34 ... Crank angle sensor 100 ... Electronic control unit (ECU) 101 ... Air-fuel ratio sensor 102 ... Sensor element 103 sensor circuit 104 heater 105 battery 106 heater circuit 110 air-fuel ratio sensor control unit (A / FCU) 200 engine

Claims (2)

[Claims] 1. An oxygen concentration detection device comprising: an air-fuel ratio sensor provided in an exhaust passage of an internal combustion engine; a heater for heating the air-fuel ratio sensor; and heater control means for controlling electric power supplied to the heater. In the specific operation of the internal combustion engine during control of power supplied to the heater by element impedance feedback of the air-fuel ratio sensor, which is performed to maintain an active state of the air-fuel ratio sensor after activation of the air-fuel ratio sensor An oxygen concentration detection device, wherein a relationship between a temperature of the heater and a resistance value of the heater is acquired based on a resistance value of the heater acquired in a state. 2. Obtaining a relationship between a temperature of the heater and a resistance value of the heater when a relationship between an element temperature and an element impedance of the air-fuel ratio sensor is different from the same relationship when the air-fuel ratio sensor is an initial product. The oxygen concentration detecting device according to claim 1, wherein the oxygen concentration detecting device is prohibited.