JP2695294B2 - Oxygen sensor abnormality detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor abnormality detecting device for detecting an abnormality in an exhaust gas purifying device for an automobile engine.

[0002]

2. Description of the Related Art Air-fuel ratio feedback control using a three-way catalyst and an oxygen sensor has been widely used to purify exhaust gas from automobile engines, and is a key part of these exhaust gas purification systems. It has become necessary to detect the abnormality of the oxygen sensor and warn the driver of the deterioration of exhaust gas.

A known example proposed as a method for detecting such an abnormality will be described below. FIG. 8 is a block diagram of a conventional oxygen sensor abnormality detection device. In the figure, 1 is an engine, 2 is an intake pipe, 3 is an injector installed in the intake pipe 2 to supply fuel to the engine 1, and 4 is an intake pipe. An air flow sensor for detecting the amount of air, 5 a throttle valve for adjusting the amount of intake air, 6 an exhaust pipe, 7 a three-way catalyst provided in this exhaust pipe 6, 8 oxygen sensitive to the exhaust gas in the exhaust pipe 6. Sensor,
Reference numeral 9 is a rotation sensor for detecting the rotation speed of the engine 1, 10 is processing various input information, calculates the basic fuel amount to be supplied to the engine 1 based on the result, controls the injector 3, and outputs the signal from the oxygen sensor 8. This is a control device that performs feedback correction of the air-fuel ratio based on the above.

Further, as shown in the block diagram of FIG. 9, the inside of the control device 10 reads various input information and performs a calculation process from the information, a calculation device 50, a ROM 51 for storing a calculation procedure and predetermined data, and a calculation time. A RAM 52 for temporarily storing the calculation result and a drive circuit 53 for driving the injector 3 based on the output of the calculation device 50.

Next, the operation will be described with reference to the flowchart of FIG. In FIG. 10, the signal from the air flow sensor 4 is sent to the arithmetic unit 50 in step S100.
Then, the signal from the rotation sensor 9 is read in step S101, the basic fuel amount is calculated based on these signals in step S102, and the basic drive pulse width of the injector 3 is calculated. Since this calculation method is widely known,
Detailed description is omitted.

Next, in step S103, the output signal of the oxygen sensor 8 is read, and in step S104 it is determined whether the value is rich or lean.
In step S106, the fuel amount reduction correction calculation is performed in step S106. If the fuel amount is lean, step S106 is performed.
From step 104 to step S105, this step S1
At 05, the fuel amount increase correction calculation is performed.

As a result, as shown in FIG. 11B, the actual air-fuel ratio responds to the rich / lean signal of the oxygen sensor 8 shown in FIG. Press to invert alternately. If the operation and responsiveness of the oxygen sensor 8 are normal, the air-fuel ratio amplitude λR remains as small as about 1%, and the purification efficiency of the three-way catalyst 7 is maintained in a good state.

However, when the oxygen sensor 8 is attacked by impurities such as lead contained in the fuel, the responsiveness deteriorates,
As shown in FIG. 12 (b), the amplitude λR of the air-fuel ratio becomes a large value, and as a result, the output of the oxygen sensor 8 shown in FIG. 12 (b) is reduced, and the purification efficiency of the three-way catalyst 7 is reduced. Not only worsens, but also has the adverse effect of hunting the engine speed due to air-fuel ratio fluctuations.

As a method of detecting such an abnormality of the oxygen sensor 8, it has been proposed to check the responsiveness of the oxygen sensor 8 in a steady state, not during a transient state such as acceleration / deceleration (California, USA). State CARB
Plan). In addition, the abnormality determination of the oxygen sensor 8 is performed as shown in FIG.
Fuel correction calculation feedback is temporarily stopped forcibly.
It will be done.

FIG. 13 is a flow chart for explaining the operation of this method. In FIG. 13, step S
After performing the basic fuel amount in 200 in the same manner as the procedure shown in FIG. 10, in step S203, the timer {calculation device (hereinafter referred to as CPU) 50 in control device 10, ROM 51, RAM
52, which has been created in advance by a program by 52, is set (started).

Next, in step S204, the amount of fuel is changed stepwise from rich to lean, then in step S205 the output signal V ₀ of the oxygen sensor 8 is read, and in step S206 the output signal V ₀ is determined to a predetermined value. level V _e less to determine whether (a lean signal) value, V _0>
If it is V _e , the process proceeds from step S206 to step S205.
Returning, the output signal V ₀ of the oxygen sensor 8 is repeatedly read, and when V ₀ <V _e , step S203.
The response time T _d from when the fuel amount is changed stepwise by the timer started in 1 to when the signal of the oxygen sensor 8 is inverted to the lean side is measured.

Next, at step S208, the response time T
_{If d} is not larger than the predetermined value T _d1 set in advance, it is determined to be normal, and if it is larger, it is determined to be abnormal and the result is stored or alarmed.

The above operation is similarly performed when the fuel amount is changed from lean to rich (in this case, step S206 satisfies T _o > T _e ). FIG. 14 shows these operations in a chart. FIG. 14 (a) shows the supplied fuel amount, FIG. 14 (b) shows the oxygen sensor output, and the relationship between the temperature of the oxygen sensor 8 and the response time. FIG. 15 is a characteristic diagram relating to abnormality determination.

In the characteristic diagram of FIG. 15, a solid curve a is a characteristic of the oxygen sensor 8 having a fast response, that is, a normal oxygen sensor.
The broken curve b indicates a poor response, that is, an abnormal oxygen sensor 8
It is the characteristic of. If the level T _d1 is set in advance as the threshold value of the response time T _d , the oxygen sensor 8 deteriorates at a temperature (eg, 300 ° C.) normally used and exhibits a characteristic curve showing an abnormal response time. b is judged to be abnormal when the temperature of the oxygen sensor 8 is about 400 ° C. or lower.
Further, as shown by the characteristic curve c, the one whose response is deteriorated is determined to be abnormal regardless of the temperature of the oxygen sensor.

[0015]

Since the conventional oxygen sensor abnormality detecting device is constructed as described above, the oxygen sensor when the air-fuel ratio is forcibly changed from lean to rich or vice versa. Since the response time of No. 8 is determined with a certain discriminant value, if the temperature of the oxygen sensor 8 becomes high, it is difficult to determine the abnormality even if the temperature is low. There was a risk that it would be erroneously determined to be abnormal.

The temperature of the oxygen sensor depends on the operating conditions (e.g., the time elapsed from the start of the engine, the number of revolutions, the load, the cooling by the running wind).
The above-mentioned misjudgment is difficult to avoid because it fluctuates greatly depending on.

The present invention has been made in order to solve the above problems, and can prevent erroneous determination of normality as abnormality caused by the temperature dependence of the response time of the oxygen sensor, and also in a wide temperature range. An object of the present invention is to obtain an abnormality detecting device for an oxygen sensor that enables determination of abnormality in the oxygen sensor.

[0018]

Means for Solving the Problems] abnormality detecting apparatus for an oxygen sensor in accordance with the present invention detects the temperature of the oxygen sensor, a temperature sensor to input the detection signal to the arithmetic unit of the control device
Provided, the response time of the oxygen sensor is a judgment value according to the detected temperature
It is judged to be abnormal when the value exceeds. In addition, this departure
The oxygen sensor abnormality detection device according to Ming
It is designed to stop when the engine accelerates or decelerates.
You.

[0019]

According to the present invention, the control device corrects the determination level of the response time of the oxygen sensor based on the detection signal of the temperature of the oxygen sensor detected by the temperature sensor, and determines the abnormality of the oxygen sensor in a wide temperature range. It acts to prevent misjudgment. In addition, according to the present invention,
Is not set when the engine is accelerating or decelerating.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an oxygen sensor abnormality detecting device of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment. In FIG. 1, the same parts as those of the conventional example shown in FIG. Mainly the parts different from.

As is apparent from a comparison between FIG. 1 and FIG. 8, the portions indicated by reference numerals 1 to 10 in FIG. 1 are the same as those in FIG. 8, and the portion indicated by reference numeral 11 is different from FIG. is there.
That is, the embodiment of FIG. 1 is characterized in that the temperature sensor 11 is newly provided in the configuration of FIG.

The temperature sensor 11 detects the temperature of the oxygen sensor 8, and the detection signal of the temperature sensor 11 is E.
It is designed to be sent to the CU 10. This ECU 10
Although the internal structure is shown in FIG. 4, it is the same as the conventional example shown in FIG. 9, and the arithmetic unit 50 (CPU) in the ECU 10 is included.
Further, as shown in FIG. 4, the detection signal of the temperature sensor 11 is input. The operation using the temperature sensor 11 will be described below based on the flowchart shown in FIG. 2 and the characteristic diagram shown in FIG.

The operation shown in the flow chart of FIG. 2 is performed by the microcomputer (CPU, CPU) in the control device 10 shown in FIG.
ROM, Ru performed by configured) in RAM. Ma
In addition, the abnormality determination of the oxygen sensor 8 is because the vehicle is accelerating or decelerating.
It is executed in steady state, not during such transient time,
The correction calculation feedback of the fuel in FIG. 10 is temporarily forced.
It is done by stopping at. In FIG. 2, first, step S
After calculating the basic fuel amount in 200, the value T _emp of the temperature sensor 11 of the oxygen sensor 11 is read in step S201, and in step S202 the response time determination value T _{do (t} ) of the oxygen sensor 8 according to this temperature T _{emp. )} Is calculated by a preset calculation formula or a table lookup. As shown in FIG. 3, the characteristic of the response time determination value T _{do (t)} with respect to the temperature T _emp becomes smaller as the temperature of the oxygen sensor 8 becomes higher. Curves a and b in FIG. 3 correspond to curves a and b in FIG. 15, respectively.

Next, from step S203 to step S2
The operation up to 07 is the same as step S203 to step S207 of FIG.
After measuring the response time T _d of the oxygen sensor 8 in step S207 in FIG. 13, it is determined in step S208a whether the response time T _d is larger than the response time determination value T _{do (t)} calculated in step S202. If it is large, it is judged as abnormal, and if it is small, it is judged as normal.

The same operation as described above when the amount of fuel stepwise varied from lean to rich is performed (step S206 becomes V _o> V _e).

When the temperature of the oxygen sensor 8 is lower than the activation temperature, it is necessary to stop the abnormality determination. This operation is step S2 in the flowchart of FIG.
This can be easily done by setting the value of the response time determination value T _{do (t)} in the temperature T _emp of 02.

By the way, as a concrete temperature detecting method by the temperature sensor 11, the following two methods can be considered. The first method is a type in which an electrothermal heater that has recently been put into practical use is built in an oxygen sensor.
This is a method of utilizing the temperature dependence of the resistance value of this heater, and when a platinum resistance is used for the heater, it can be used as a good temperature sensor. An example of this characteristic is shown in FIG. 5, and an example of the structure is shown in FIGS.

As a specific method for detecting the temperature from the resistance value of the heater, there is a method of measuring the resistance value of the heater by temporarily stopping energization of the heater during temperature measurement. Further, it can be obtained from the voltage applied to the heater and the energization current in the energized state of the heater.

The second method is the most general one,
As shown in FIG. 6, a temperature sensor 11 such as a thermistor or platinum is added inside or outside the oxygen sensor 8. FIG. 7 is a cross-sectional view of FIG. 6, showing the internal configuration of the oxygen sensor 8.

As is apparent from FIG. 7, a case 8a having a plurality of holes is brought into contact with the exhaust gas A, and a flange 8b is attached near the upper end of the case 8. By attaching this flange 8b to the exhaust pipe, the exhaust gas A exhausted through the exhaust pipe 6
Oxygen ions in the exhaust gas A are detected by the zirconia element 8c (the ceramic is coated with a solid electrolyte) inside the case 8a through the hole a. An atmosphere side platinum electrode 8d is provided on the inner surface of the zirconia element 8c, and an exhaust side platinum electrode 8d is provided on the outer surface.
e is provided. A heater 8f is inserted at a predetermined distance from the atmosphere-side platinum electrode 8d. This heater 8f
And the atmosphere side platinum electrode 8d, the atmosphere flows between the heater 8 and
The temperature of f is detected by the temperature sensor 11.

[0031]

As described above, according to the present invention, when the abnormality due to the deterioration of the oxygen sensor is discriminated from the response time when the air-fuel ratio is stepwise changed, the discrimination time is determined by the oxygen sensor. Since it is configured to change depending on the temperature, it is possible to prevent erroneous determination (determining normal as abnormal) that occurs due to the temperature dependence of the response time of the oxygen sensor, and it is possible to determine the abnormality of the oxygen sensor in a wide temperature range. There is. Further, according to the present invention, the abnormality determination of the oxygen sensor
The output of the oxygen sensor
Since this is done in a stable state,
Regular judgment can be performed accurately.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an abnormality detecting device for an oxygen sensor according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a flow of operation of the abnormality detection device for the oxygen sensor of FIG.

3 is an abnormality determination characteristic diagram of an oxygen sensor used in the oxygen sensor abnormality detection device of FIG.

4 is a block diagram showing an internal configuration of a control device in the oxygen sensor abnormality detection device of FIG. 1. FIG.

5 is a characteristic diagram of a heater resistance value of an oxygen sensor with a built-in heater used in the abnormality detecting device for the oxygen sensor of FIG.

6 is a front view showing an arrangement example of temperature sensors in the oxygen sensor applied to the abnormality detection device for the oxygen sensor of FIG. 1. FIG.

7 is a cross-sectional view showing the configuration of the oxygen sensor of FIG.

FIG. 8 is a block diagram showing a configuration of a conventional oxygen sensor abnormality detection device.

9 is a block diagram showing an internal configuration of a control device in the oxygen sensor abnormality detection device of FIG. 8. FIG.

10 is a flowchart showing a calculation procedure of a control device in the abnormality detection device of the oxygen sensor of FIG.

11 is a waveform chart showing the relationship between the output of the oxygen sensor and the air-fuel ratio, for explaining the operation of the abnormality detection device for the oxygen sensor of FIG.

FIG. 12 is a waveform diagram showing the relationship between the output of the oxygen sensor and the air-fuel ratio for explaining the operation of the abnormality detection device for the oxygen sensor of FIG.

13 is a flowchart showing a flow of operations for detecting abnormality in the oxygen sensor in the abnormality detecting device for oxygen sensor in FIG.

14 is a waveform diagram of the oxygen sensor in the abnormality detection device for the oxygen sensor of FIG.

15 is a characteristic diagram of oxygen sensor abnormality determination in the oxygen sensor abnormality detection device of FIG.

[Explanation of symbols]

 1 Engine 2 Intake Pipe 3 Injector 4 Air Flow Sensor 5 Throttle Valve 6 Exhaust Pipe 7 Three-way Catalyst 8 Oxygen Sensor 9 Rotation Sensor 10 Control Device 11 Temperature Sensor 50 Computing Device 51 ROM 52 RAM 53 Drive Circuit

Claims (2)

(57) [Claims] 1. An oxygen sensor for detecting an air-fuel ratio from an exhaust gas component of an engine, an air flow sensor for detecting an intake air amount of the engine, a rotation sensor for detecting an engine speed, and a fuel for supplying the engine. a temperature sensor for detecting an injector, a temperature of the oxygen sensor, the upper
Calculate the basic fuel amount from the intake air amount and the above speed
Then, based on the signal from the oxygen sensor,
Fuel to the above engine by correcting the feedback
A means for controlling the amount of fuel and a predetermined amount when the fuel control is stopped.
At the timing, the air-fuel ratio is rich across the stoichiometric air-fuel ratio.
Steps from lean to lean or vice versa
Let the oxygen sensor rich to lean or vice versa.
The response time until it changes to
When the response time judgment value changed according to
An abnormality detection device for an oxygen sensor, comprising: means for determining that the sensor is abnormal . 2. The abnormality determination is such that the operation is stopped when the engine is accelerated or decelerated.
Abnormality detection device for the oxygen sensor described.