JPH08110320A - Oxygen sensor heater diagnostic device - Google Patents

Abstract

(57) [Abstract] [Purpose] To diagnose the deterioration of the heater provided in the oxygen sensor with high accuracy. [Structure] The capacity of a heater provided in an oxygen sensor is calculated as heater capacity = heater current × heater applied voltage (S6). On the other hand, the engine speed Ne and the basic fuel injection amount T
The current exhaust gas temperature is estimated based on p (S4), and the heater capacity threshold value is set based on the exhaust gas temperature and the heater applied voltage (S5). Then, the calculated heater capacity is compared with a threshold value (S7), and if the current heater capacity is smaller than the threshold value, it is determined whether the heater is deteriorated (S).
8).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor heater diagnosing device, and more particularly, to a device for diagnosing heater deterioration.

[0002]

2. Description of the Related Art Conventionally, the air-fuel ratio of an engine intake air-fuel mixture is detected based on the oxygen concentration in exhaust gas, and the fuel supply amount to the engine is fed back so that the air-fuel ratio of the engine intake air-fuel mixture approaches a target air-fuel ratio. An air-fuel ratio feedback control for controlling is known (see Japanese Patent Laid-Open No. 60-240840).

As an oxygen sensor used for detecting the oxygen concentration, for example, electrodes are formed on the inner and outer surfaces of a zirconia tube, respectively, and the oxygen concentration in the atmosphere (reference oxygen concentration) introduced into the inside of the tube and the outside engine. Generate an electromotive force between the electrodes according to the ratio with the oxygen concentration in the exhaust gas,
By monitoring this electromotive force, there is one that indirectly detects the oxygen concentration in the exhaust gas, and thus the rich / lean ratio to the stoichiometric air-fuel ratio of the engine intake air-fuel mixture (Actual No. Sho 63-51).
273, etc.).

In the above oxygen sensor, the sensor element may become inactive at a low exhaust temperature and the desired output characteristics may not be obtained. Therefore, for example, in the above zirconia tube type oxygen sensor, the zirconia tube is used. The oxygen sensor is activated even during low temperature exhaust by inserting a rod-shaped heater into the hollow part of the engine and turning the heater on / off based on information such as engine speed and exhaust temperature, or by constantly energizing it. In some cases, the desired air-fuel ratio feedback control can be performed as in the high exhaust temperature state.

As the structure of the oxygen sensor, in addition to the tube type, there is a structure in which a plurality of sheets are laminated to form a sensor element. In the oxygen sensor having such a structure, a heater wire is sandwiched between the sheets. .

[0006]

By the way, in the oxygen sensor having the heater as described above, there is a method of diagnosing the deterioration of the heater based on the detection result of the heater capacity, but it is fixed with the detected heater capacity. Since the configuration is such that the presence or absence of heater deterioration is diagnosed by comparison with a threshold value, there is a risk of erroneous determination of heater deterioration.

That is, assuming that the heater capacity is heater capacity = heater current × heater applied voltage, the heater current (heater resistance) changes depending on the heater applied voltage and also changes depending on the exhaust temperature (FIGS. 8)), the heater capacity characteristic is actually as shown in FIG. Therefore, when comparing the heater capacity calculated based on the heater current and the heater applied voltage with a fixed threshold value, on the high exhaust temperature side where the heater capacity is small, even if there is no deterioration, a heater smaller than the threshold value is used. The capacity may be detected and the heater deterioration may be erroneously determined, and on the low exhaust temperature side where the heater capacity becomes large, a heater capacity larger than the threshold value is detected even though deterioration has occurred, There was a possibility that the judgment would be normal.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a diagnostic device capable of diagnosing heater deterioration with high accuracy without being affected by the heater applied voltage and exhaust temperature.

[0009]

Therefore, in the oxygen sensor heater diagnosing device according to the invention of claim 1, the heater provided in the oxygen sensor whose output value changes in response to the oxygen concentration in the engine exhaust is diagnosed. The device is configured as shown in FIG. In FIG. 1, the heater capacity calculation means calculates the capacity of the heater based on the current flowing through the heater and the voltage applied to the heater.

On the other hand, the threshold value setting means sets the heater capacity threshold value based on the exhaust gas temperature of the engine detected by the exhaust gas temperature detecting means and the voltage applied to the heater.
The deterioration diagnosing means determines the deterioration of the heater based on a comparison between the threshold value set by the threshold value setting means and the heater capacity calculated by the heater capacity calculating means.

In the oxygen sensor heater diagnosing device according to the second aspect of the present invention, the exhaust gas temperature detecting means estimates the exhaust gas temperature of the engine based on the engine operating conditions.
In the oxygen sensor heater diagnosing device according to the invention of claim 3, the exhaust gas temperature detecting means is configured to directly detect the exhaust gas temperature by an exhaust gas temperature sensor that detects the exhaust gas temperature in the vicinity of the oxygen sensor. .

In the oxygen sensor heater diagnosing device according to the fourth aspect of the present invention, the threshold value setting means sets the threshold value smaller as the exhaust gas temperature is higher.

[0013]

According to the heater diagnosing device for an oxygen sensor of the first aspect of the present invention, the heater capacity is compared with a threshold value set based on the heater applied voltage and the exhaust temperature to diagnose the deterioration of the heater. Therefore, it is possible to eliminate the fluctuation of the heater capacity due to the change of the applied voltage or the exhaust temperature and diagnose only the change of the heater capacity due to the deterioration of the heater.

According to the diagnosing device for the heater for the oxygen sensor of the second aspect of the present invention, the exhaust temperature is estimated from the engine operating conditions, so that even in a system that does not have a sensor for directly detecting the exhaust temperature, the system can be adapted to the exhaust temperature. The threshold can be set. According to the diagnosing device of the heater for an oxygen sensor of the third aspect, the exhaust gas temperature is directly detected in the vicinity of the oxygen sensor, so that the exhaust gas temperature can be detected with high accuracy.

In the oxygen sensor heater diagnosing device according to the fourth aspect of the present invention, the threshold value is set smaller as the exhaust gas temperature is higher. Therefore, the threshold value is set in accordance with the increase in the heater resistance as the exhaust gas temperature rises. Can be set.

[0016]

Embodiments of the present invention will be described below. In FIG. 2 showing an embodiment, air is drawn into an internal combustion engine 1 from an air cleaner 2 through an intake duct 3, a throttle valve 4 and an intake manifold 5. At each branch portion of the intake manifold 5, a fuel injection valve 6 is provided for each cylinder. This fuel injection valve 6 is an electromagnetic fuel injection valve that is energized by a solenoid to open the valve, and deenergized to close the valve, which is energized by a drive pulse signal from a control unit 12 described later to open the valve. Fuel, which is pumped from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator, is injected and supplied to the engine 1.

Each combustion chamber of the engine 1 is provided with an ignition plug 7, which ignites a spark to ignite and burn an air-fuel mixture. Exhaust gas is discharged from the engine 1 through the exhaust manifold 8, the exhaust duct 9, the three-way catalyst 10, and the muffler 11. The control unit 12 is a CPU, RO
An M, RAM, an A / D converter, a microcomputer including an input / output interface, and the like are provided, input signals from various sensors are received, and arithmetic processing is performed as described later to operate the fuel injection valve 6. To control.

As the various sensors, the intake duct 3 is used.
An air flow meter 13 is provided therein and outputs a signal according to the intake air flow rate Q of the engine 1. Further, the crank angle sensor 14 is provided, and in the case of the four cylinders of the present embodiment, the reference crank angle signal REF for each crank angle of 180 °.
And a unit crank angle signal P for each crank angle of 1 ° or 2 °
And OS are output. Here, the reference crank angle signal REF
The engine rotation speed Ne can be calculated by measuring the number of the unit crank angle signals POS generated in the cycle or in a predetermined time.

A water temperature sensor 15 for detecting a cooling water temperature Tw of the water jacket of the engine 1 is provided.
Further, an oxygen sensor 16 is provided in the collecting portion of the exhaust manifold 8, and the output of the oxygen sensor 16 changes in response to the oxygen concentration in the exhaust gas so that the air-fuel ratio of the engine intake air-fuel mixture can be detected. Has become.

As shown by an equivalent circuit in FIG. 2, the oxygen sensor 16 is a kind of concentration battery that generates an electromotive force according to the ratio of the oxygen concentration in the exhaust gas to the oxygen concentration in the atmosphere. It is a known method for detecting the rich lean of the actual air-fuel ratio with respect to the theoretical air-fuel ratio by utilizing the fact that the oxygen concentration in the inside suddenly changes at the stoichiometric air-fuel ratio. In the present embodiment, the oxygen sensor 16 is provided with a heater 16a for activating the sensor element even in a low exhaust gas temperature state and maintaining a desired detection characteristic (activated state).
A power supply voltage (battery voltage) is applied via the ignition switch 17.

The oxygen sensor 16 may be constructed by laminating sheet-like members other than the zirconia tube type, and is not limited to the structure for detecting only the stoichiometric air-fuel ratio as described above. It may be a sensor that can detect the air-fuel ratio in a wide range. Here, the CPU of the microcomputer built in the control unit 12 is based on the output of the oxygen sensor 16 when the predetermined air-fuel ratio feedback control condition is satisfied, and the actual air-fuel ratio (target air-fuel ratio) is actually calculated. The rich lean of the air-fuel ratio of
Based on the discrimination result, the air-fuel ratio feedback correction coefficient LMD is, for example, proportionally / integral controlled so that the actual air-fuel ratio approaches the stoichiometric air-fuel ratio. Then, the basic fuel injection amount Tp calculated based on the intake air flow rate Q and the engine rotation speed Ne.
Is corrected and set by the air-fuel ratio feedback correction coefficient LMD, and the fuel injection valve 6 is set based on the corrected injection amount.
Control the valve opening time of.

Further, the control unit 12 diagnoses the deterioration of the heater 16a of the oxygen sensor 16 as shown in the flowchart of FIG. In this example,
As shown in the flow chart of FIG. 3, the control unit 12 has software functions of the heater capacity calculating means, the exhaust temperature detecting means, the threshold setting means, and the deterioration diagnosing means.

In the flowchart of FIG. 3, first, in step 1 (denoted as S1 in the figure, the same applies hereinafter),
It is judged whether the ignition switch 17 is ON or OFF.
When it is N, the routine proceeds to step 2, where it is judged whether or not the engine is operating based on the engine speed Ne and the intake air flow rate Q. Then, when the engine is operating, the routine proceeds to step 3, where the voltage applied to the heater 16a (battery voltage) is detected.

In the next step 4, the exhaust gas temperature under the present operating conditions is estimated based on the basic fuel injection amount Tp representing the engine load and the engine rotation speed Ne (FIG. 4).
reference). As described above, if the exhaust temperature is estimated based on the engine operating condition, the heater 16a can be diagnosed for deterioration based on the exhaust temperature even if the exhaust temperature sensor is not provided, and the system configuration is inexpensive. Becomes

Here, an exhaust gas temperature sensor for directly detecting the exhaust gas temperature in the vicinity of the oxygen sensor 16 may be provided. In this case, the exhaust gas temperature can be detected with high accuracy. In step 5, as shown in FIG. 5, a threshold value corresponding to the current exhaust gas temperature and applied voltage is set by referring to a map in which the threshold value of the heater capacity is stored in advance using the exhaust gas temperature and the heater applied voltage as parameters. .

The map is set corresponding to the change in the heater capacity due to the heater applied voltage and the exhaust temperature,
The threshold value is set to a smaller value when the exhaust gas temperature is high and the heater capacity is small because the heater resistance increases. In step 6, the current heater capacity is calculated as: heater capacity = heater current × heater applied voltage.

Then, in step 7, step 6
The current heater capacity calculated in step 5 is compared with the threshold value obtained in step 5 by referring to the map. Here, when the current heater capacity is smaller than the threshold value, it is determined that the heater is deteriorated, and the process proceeds to step 8 to perform the deterioration determination. On the other hand, when the current heater capacity is equal to or greater than the threshold value, it is determined that the heater has not deteriorated, and the process proceeds to step 9 to determine whether the heater 16a is normal.

Thus, according to this embodiment, the heater 16a
By setting the threshold value based on the heater applied voltage and the exhaust temperature that cause the heater capacity to change regardless of the deterioration of the heater capacity, even if the heater applied voltage or the exhaust temperature changes, the heater capacity due to the deterioration of the heater 16a It is possible to discriminate only the decrease of the above, and it is possible to provide a highly accurate diagnostic result. When the deterioration determination is performed in step 8, the fail to stop the air-fuel ratio feedback control using the oxygen sensor 16 at a predetermined low exhaust temperature at which the oxygen sensor 16 cannot be activated unless it is heated by the heater 16a. To run safe,
Alternatively, the driver may be warned of the occurrence of deterioration of the heater 16a.

[0029]

As described above, according to the diagnostic device for an oxygen sensor heater according to the first aspect of the present invention, fluctuations in the heater capacity due to changes in applied voltage and exhaust temperature are eliminated,
There is an effect that only the change in the heater capacity due to the deterioration of the heater can be accurately diagnosed.

According to the oxygen sensor heater diagnosing device of the second aspect of the present invention, it is possible to set the threshold value according to the exhaust temperature even in a system that does not include a sensor for directly detecting the exhaust temperature. According to the diagnosing device of the heater for an oxygen sensor of the third aspect, the exhaust gas temperature is directly detected in the vicinity of the oxygen sensor, so that the exhaust gas temperature can be detected with high accuracy.

In the oxygen sensor heater diagnosing device according to the fourth aspect of the present invention, the threshold value is set smaller as the exhaust gas temperature is higher. Therefore, the threshold value is set in correspondence with the increase in the heater resistance as the exhaust gas temperature rises. The effect is that it can be set.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of a diagnostic device according to the invention of claim 1.

FIG. 2 is a diagram showing a system configuration showing an embodiment.

FIG. 3 is a flowchart showing deterioration diagnosis control of the embodiment.

FIG. 4 is a diagram showing estimation control of exhaust temperature according to operating conditions.

FIG. 5 is a diagram showing how the heater capacity changes based on exhaust temperature and applied voltage.

FIG. 6 is a diagram showing a change in heater surface temperature due to exhaust temperature and applied voltage.

FIG. 7 is a diagram showing changes in heater surface temperature due to exhaust temperature and applied voltage.

FIG. 8 is a diagram showing a correlation between heater surface temperature and heater resistance.

[Explanation of symbols]

 1 Engine 12 Control Unit 13 Air Flow Meter 14 Crank Angle Sensor 16 Oxygen Sensor 16a Heater 17 Ignition Switch

Claims (4)

[Claims] 1. A heater diagnostic device for an oxygen sensor for diagnosing a heater provided in an oxygen sensor, the output value of which changes in response to an oxygen concentration in engine exhaust gas, the capacity of the heater flowing to the heater. Heater capacity calculating means for calculating based on current and voltage applied to the heater, exhaust temperature detecting means for detecting the exhaust temperature of the engine, exhaust temperature detected by the exhaust temperature detecting means and voltage applied to the heater Threshold value setting means for setting the threshold value of the heater capacity based on the above, and the deterioration determination of the heater based on the comparison between the threshold value set by the threshold value setting means and the heater capacity calculated by the heater capacity calculating means. A diagnostic device for an oxygen sensor heater, comprising: a deterioration diagnosing means for performing. 2. The oxygen sensor heater diagnostic device according to claim 1, wherein the exhaust temperature detecting means estimates the exhaust temperature of the engine based on engine operating conditions. 3. The exhaust gas temperature detecting means directly detects the exhaust gas temperature by an exhaust gas temperature sensor which detects the exhaust gas temperature at a position near the oxygen sensor.
The heater diagnostic device for the oxygen sensor described above. 4. The diagnostic device for an oxygen sensor heater according to claim 1, wherein the threshold value setting means sets the threshold value smaller as the exhaust gas temperature is higher.