JP2913694B2 - Exhaust gas sensor failure detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a failure detection device for an exhaust gas sensor that detects a failure of a heater of an exhaust gas sensor with a heater used for feedback control of an air-fuel ratio.

[Conventional technology]

2. Description of the Related Art Conventionally, as disclosed in Japanese Patent Application Laid-Open No. 62-12382, an oxygen sensor (exhaust gas sensor) for detecting oxygen concentration in exhaust gas is provided in an exhaust passage of an engine, and an air-fuel ratio is determined in accordance with the output of the oxygen sensor. Feedback control, that is, if the air-fuel ratio detected by the output of the oxygen sensor is rich, the fuel supply amount is corrected in the decreasing direction, and if the air-fuel ratio is lean, the fuel supply amount is corrected in the increasing direction. An air-fuel ratio control device that is configured to be repeated is generally known.

In such a device, a heater-equipped exhaust gas sensor having a heater for activating the sensor attached to the oxygen sensor has been conventionally used.

[Problems to be solved by the invention]

When feedback control of the air-fuel ratio is performed by detecting the oxygen concentration using an exhaust gas sensor with a heater, even if the oxygen sensor itself is normal, if the heater fails, the sensor output characteristics change, and therefore, the air-fuel ratio that is feedback-controlled is reduced. There is a problem that it deviates from an appropriate value.

That is, when the heater is normal and the heater has not failed, the sensor output characteristic is shown by a solid line in FIG. 4, and at a predetermined threshold voltage Vs corresponding to the stoichiometric air-fuel ratio (λ = 1) at this time, Whether the air-fuel ratio is rich or lean is detected based on whether the output voltage of the sensor is higher or lower than the threshold, and feedback control is performed accordingly. However, when the heater fails, the output characteristics of the sensor change as shown by the broken line in FIG. 4, and a deviation occurs between the threshold voltage Vs and the stoichiometric air-fuel ratio (λ = 1). Therefore, when the heater fails, feedback control is performed to the air-fuel ratio that deviates from the request. If the air-fuel ratio shifts due to the failure of the heater in this way, the emission deteriorates. For example, as shown in FIG. 5, when the heater fails (shown by b) as compared with the normal state (shown by a). Problems such as an increase in NOx occur.

In order to cope with such a problem, it is necessary to accurately detect a failure of the heater.

In view of such circumstances, the present invention can accurately detect when a heater has failed even if the oxygen sensor itself is normal, and can detect a failure of the exhaust gas sensor that can cope with a heater failure. An apparatus is provided.

[Means for solving the problem]

In order to achieve the above object, the invention according to claim 1 includes an oxygen sensor that detects an oxygen concentration in exhaust gas and outputs a detection signal to a control unit that performs feedback control of an air-fuel ratio. An exhaust gas sensor failure detecting device for detecting a failure of the heater in an exhaust gas sensor having an attached heater for activating the sensor, a comparing means for comparing an output of the oxygen sensor with a set value, and the comparing means Based on the comparison, the sensor output rise time from the start of energization to the heater until the output of the oxygen sensor becomes equal to or more than the set value is measured. When the sensor output rise time is equal to or longer than a predetermined time, Failure determination means for determining that the heater has failed.

Further, the invention according to claim 2 is an oxygen sensor which detects an oxygen concentration in exhaust gas and outputs a detection signal to a control means for performing feedback control of an air-fuel ratio by a feedback correction amount corresponding to the oxygen concentration; An exhaust gas sensor failure detection device for detecting a failure of the heater in an exhaust gas sensor having a heater for sensor activation attached to the sensor, and a comparing means for comparing an output of the oxygen sensor with a set value. Failure determination for determining the presence or absence of a heater failure by measuring the sensor output rise time from the start of energization of the heater to the output of the oxygen sensor becoming equal to or greater than a set value based on the comparison by the comparing means. Means for correcting the calculation of the feedback correction amount by the control means when a failure is determined by the failure determination means. It is those with a door.

[Action]

According to the above configuration, when the heater fails, the failure is detected by utilizing the fact that the sensor output rise time is longer than normal. Further, as in the invention according to the second aspect, when a correction means for correcting the calculation of the feedback correction amount by the control means when it is determined that the heater has failed is provided, the output characteristic of the oxygen sensor due to the heater failure can be reduced. The air-fuel ratio is corrected for the change.

〔Example〕

 An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of an air-fuel ratio control device including a failure detection device according to the present invention. In this figure, an intake port 5 and an exhaust port 6 are formed in an engine body 1 and open to a combustion chamber 2 and opened and closed by intake valves 3 and exhaust valves 4, respectively. An intake passage 7 communicates with the intake port 5. An exhaust passage 8 communicates with the exhaust port 6.

An air flow meter 9, a throttle valve 10, and a fuel injection valve 11 are arranged in the intake passage 7.

On the other hand, the exhaust passage 8 is provided with an exhaust gas sensor having an oxygen sensor 12 and a sensor activation heater 13 attached thereto. The oxygen sensor 12 detects the air-fuel ratio of the air-fuel mixture by detecting the oxygen concentration in the exhaust gas. In this embodiment, the oxygen sensor 12 is formed of a λ sensor having a λ characteristic as shown in FIG. 4 as an output characteristic with respect to the air-fuel ratio. The characteristics of the oxygen sensor 12 are as shown by the solid line in FIG. 4 when the heater 13 is ON, and are as shown by the broken line in FIG. 4 when the heater 13 is OFF (failure).

The output of the oxygen sensor 12 is input to a control unit (ECU) 15 shown in FIG. The control unit 15 includes an air-fuel ratio control unit 16 that feedback-controls the air-fuel ratio by a feedback correction amount corresponding to the oxygen concentration detected by the oxygen sensor 12,
Comparison means 17 and failure determination means 18 constituting the failure detection device
And correction means 19 for correcting the calculation of the feedback correction amount by the air-fuel ratio control means 16 when a failure is determined by the failure determination means.

The air-fuel ratio control unit 16 obtains a basic injection amount based on an intake air amount detection unit from the air flow meter 9 and an engine speed detection signal from a speed sensor 20.
The fuel injection amount is increased or decreased by increasing or decreasing the feedback correction amount according to the output of the oxygen sensor 12, obtaining the final injection amount from the basic injection amount and the feedback correction amount, and outputting an injection pulse corresponding thereto to the fuel injection valve 11. Control. The increase / decrease of the feedback correction amount according to the output of the oxygen sensor 12 is performed, for example, as shown in FIG.
That is, the output voltage V ₀ of the oxygen sensor 12 becomes the threshold voltage Va.
(0.45V), the specified delay time T
After dr, the feedback correction amount is changed in the fuel decreasing direction by proportional and differential control, and the output voltage V ₀ is changed to the threshold voltage Va.
When it becomes lower, the feedback correction amount is changed in the fuel increasing direction by proportional and differential control after a predetermined delay time Tdl. The above delay time Tdr, Tdl
Is provided to prevent erroneous control due to noise and the like.

Further, the comparing means 17 compares the output of the oxygen sensor 12 with a set value after the power supply to the heater 13 and when the output becomes equal to or higher than the set value (when the sensor output rises), and detects the failure. Reference numeral 18 denotes the oxygen sensor 12 based on the comparison by the comparing means 17 after the energization of the heater 13 is started.
The rise time of the sensor output until the output becomes equal to or more than the set value is measured, and when the rise time of the sensor output exceeds the predetermined time, it is determined that the heater 13 has failed. When this failure is detected, the correcting means 19 causes the ratio (Tdr / Td) of the two delay times Tdr and Tdl to be detected.
l) is changed with respect to the normal state. Specifically, as shown by the broken line in FIG. 3, the change in the feedback correction amount after the sensor output exceeds the threshold voltage Vs is changed in the fuel decreasing direction. The delay time Tdr before switching to is changed to be longer.

The heater 13 by the comparing means 17 and the failure determining means 18
FIG. 2 is a flowchart showing a specific example of the detection of a failure and the correction processing by the correction means 19 in accordance with the detection.

The routine shown in this flowchart is started with the ignition on, the first output voltage V ₀ which the oxygen sensor 12 in step S ₁ as compared to the threshold voltage (set value) Vs, the by whether exceeds the threshold voltage Vs It is checked whether or not the output voltage V ₀ has risen. Until the output voltage V ₀ rises, the process returns to step S ₁ via an open loop main routine (step S ₂ ) for performing open loop control of both fuel injections.

Output voltage V ₀ which the oxygen sensor 12 in step S ₁ is the threshold voltage
When it is determined that exceeds Vs, in step S _3, the time up to this point from the start (sensor output rise time) a predetermined time Tt for failure determination of T _0, which corresponds to the sensor output rise time at normal Compare with Then, if it is within the sensor output rise time T ₀ is a predetermined time, in step S _4, the delay time Tdr, the ratio of Tdl (Tdr / Tdl) the normal value A / A '(for example, 90 ms / 40 ms) Suruga, the sensor output rise time T ₀ is determined that the failure of the heater 13 if exceeds a predetermined time, in step S _5, the ratio (Tdr / Tdl) the normal value a / a 'is greater than a predetermined value B / B '(for example, 135ms /
40ms).

In step S ₆ Following Step S ₄ or step S _5, to perform a feedback control routine for feedback controlling the air-fuel ratio in accordance with the output of the oxygen sensor 12 as described above. Then, step in step S ₇ until it became a control end condition of the ignition off or the like is determined
Repeat S _6, to the end if the control end condition.

According to the apparatus of this embodiment, steps S ₁ and S ₂
By examining the time T ₀ from the start until the output of the oxygen sensor 12 rises, the failure of the heater 1 is accurately determined. That is, if the heater 13 is turned off due to the failure, the sensor output rise time Since T ₀ becomes longer, this failure is detected by the above determination.

Further, at the time of failure detection, delay time Tdr in the feedback control of the air-fuel ratio, by the ratio of Tdl (Tdr / Tdl) is larger than normal (step S _5), the deviation of the air-fuel ratio at the time of heater fault is corrected You. That is, when the heater fails, the characteristics of the oxygen sensor 12 change as indicated by the broken line in FIG. 4, and the air-fuel ratio corresponding to the threshold voltage Vs shifts to the lean side. The controlled air-fuel ratio is biased toward the lean side. On the other hand, if the ratio (Tdr / Tdl) is increased at the time of a heater failure, as is clear from FIG. 3, the time during which the feedback correction amount is in the fuel increasing direction is increased, so that the air-fuel ratio becomes rich. Corrected in the direction. This improves emissions.

In FIG. 5, the horizontal axis represents the amount of NOx in the exhaust gas, and the vertical axis represents the amount of CO in the exhaust gas. The same feedback is obtained when the exhaust gas component is normal (point a) and when the heater fails. When the control is performed (point b), and when the above correction is performed when the heater fails (point c).
As is apparent from this figure, when the same feedback control as in normal operation is performed when the heater fails, NOx increases due to lean air-fuel ratio. On the other hand, when the above correction is made, NOx and CO fall within the allowable range ( (Shaded area).

〔The invention's effect〕

As described above, the present invention detects a failure of the heater in the exhaust gas sensor in which the heater is attached to the oxygen sensor, and the output of the oxygen sensor becomes equal to or more than the set value after the power supply to the heater is started. Since the sensor output rise time is measured until the sensor output rise time is longer than a predetermined time, it is determined that the heater is faulty. When the characteristic of the sensor changes, the failure can be accurately detected. Therefore, in the air-fuel ratio feedback control using the exhaust gas sensor with a heater, it is possible to cope with a heater failure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an embodiment of an air-fuel ratio control device including a failure detection device according to the present invention, FIG. 2 is a flowchart showing an example of processing such as failure detection, and FIG. FIG. 4 is an explanatory diagram showing a relationship between a change in the output of the oxygen sensor and a change in the feedback correction amount, FIG. 4 is a diagram showing characteristics of the oxygen sensor output with respect to the air-fuel ratio, and FIG. FIG. 5 is a diagram showing exhaust gas components when the air-fuel ratio control is modified when the heater is normal, when the heater fails, and when the heater fails. 11 ... fuel injector, 12 ... oxygen sensor, 13 ... heater,
15 ... control unit, 16 ... air-fuel ratio control means,
17: comparison means, 18: failure determination means.

Claims (2)

(57) [Claims] An exhaust gas having an oxygen sensor for detecting a concentration of oxygen in the exhaust gas and outputting a detection signal to control means for feedback-controlling an air-fuel ratio, and a heater for activating the sensor attached to the oxygen sensor. A failure detection device for an exhaust gas sensor that detects a failure of the heater in the sensor, comprising: a comparing unit that compares an output of the oxygen sensor with a set value; and starting power supply to the heater based on the comparison by the comparison unit. And a failure determination unit that measures a sensor output rising time from when the output of the oxygen sensor becomes equal to or more than the set value and determines that the heater is faulty when the sensor output rising time is equal to or longer than a predetermined time. A failure detection device for an exhaust gas sensor, comprising: 2. An oxygen sensor for detecting an oxygen concentration in exhaust gas and outputting a detection signal to control means for feedback-controlling an air-fuel ratio based on a feedback correction amount corresponding to the oxygen concentration, and an oxygen sensor attached to the oxygen sensor. An exhaust gas sensor failure detector for detecting a failure of the heater in an exhaust gas sensor having a heater for sensor activation,
Comparing means for comparing the output of the oxygen sensor with a set value;
Based on the comparison by the comparing means, a failure to determine the presence / absence of a failure of the heater by measuring a sensor output rise time from the start of energization to the heater to the output of the oxygen sensor becoming equal to or more than a set value. A failure detection device for an exhaust gas sensor, comprising: a determination unit; and a correction unit that corrects the calculation of the feedback correction amount by the control unit when the failure determination unit determines that a failure has occurred.