JPH04272444A - Failure sensing device for oxygen sensor - Google Patents

Abstract

PURPOSE:To prevent misjudging resulting from the temp. dependency of the response time of oxygen sensor by varying the judging time in compliance with the response time of the oxygen sensor in case failure due to its deterioration is to be judged from the response time when the air-fuel ratio is changed. CONSTITUTION:The temp. of an oxygen sensor 8 to sense the air-fuel ratio of an engine 1 is sensed by a temp. sensor 11. A control device 10 calculates the feedback correction calculation value of air-fuel ratio on the basis of sensing signals of are air flow sensor 4, rotation sensor 9, and oxygen sensor 8. Judgement is made for the condition that the air-fuel ratio goes across the theoretical air-fuel ratio at the specified timing and varies between the lean and the rich. The fuel amount to the engine 1 is controlled on the basis of these conditions. When the air-fuel ratio at the stop of the corrective calculation has varied, judgement is placed that the oxygen sensor 8 goes failure if its response time has exceeded the response time judging value which is varied according to the sensed temp. by the temp. sensor 11.

Description

[Detailed description of the invention]

0001

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

0002

[Prior Art] Air-fuel ratio feedback control using a three-way catalyst and an oxygen sensor has been widely used to purify the exhaust gas of automobile engines. It has become necessary to detect abnormalities in oxygen sensors and warn drivers of deterioration of exhaust gas.

[0003] A known example proposed as a method for detecting such an abnormality will be described below. FIG. 8 is a configuration diagram of a conventional abnormality detection device for an oxygen sensor. In the figure, 1 is an engine, 2 is an intake pipe, 3 is an injector installed in the intake pipe 2 and supplies fuel to the engine 1, and 4 is an intake pipe. An air flow sensor that detects the amount of air, 5 a throttle valve that adjusts the amount of intake air, 6 an exhaust pipe, 7 a three-way catalyst provided in the exhaust pipe 6, 8 an oxygen sensor that responds to the exhaust gas in the exhaust pipe 6 sensor,
9 is a rotation sensor that detects the rotation speed of the engine 1; 10 is a rotation sensor that processes various input information, and based on the results calculates the basic amount of fuel to be supplied to the engine 1 to control the injector 3; This is a control device that performs feedback correction of the air-fuel ratio based on the air-fuel ratio.

Further, inside the control device 10, as shown in the block diagram of FIG. 9, there is an arithmetic unit 50 that reads various input information and performs arithmetic processing from that information, an RON 51 that stores arithmetic procedures and predetermined data, and a It consists of a RAM 52 for temporarily storing calculation results, and a drive circuit 53 that drives the injector 3 based on the output of the calculation device 50.

Next, the operation will be explained according to the flowchart shown in FIG. In this FIG. 10, in step S100, the signal of the air flow sensor 4 is input to the arithmetic unit 50.
In step S101, the signals from the rotation sensor 9 are read, and in step S102, the basic fuel amount is calculated based on these signals, and the basic drive pulse width of the injector 3 is calculated. This calculation method is widely known, so
Detailed explanation will be 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, and if it is rich,
Proceeding to step S106, a fuel reduction correction calculation is performed in step S106, and if the fuel is lean, step S106 is performed.
The process advances from step S104 to step S105, and this step S1
In step 05, a fuel increase correction calculation is performed.

As a result, the actual air-fuel ratio is as shown in FIG. 11(b).
As shown in FIG. 11(a), in response to the rich/lean signal from the oxygen sensor 8 shown in FIG. 11(a), the integral waveform alternately inverts while crossing the stoichiometric air-fuel ratio. Operation of oxygen sensor 8,
If the response is normal, the amplitude λR of the air-fuel ratio remains at a small value of 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 takes on a large value. As a result, the output of the oxygen sensor 8 shown in FIG. 12(b) decreases, and the purification efficiency of the three-way catalyst 7 decreases. Not only does this significantly worsen the air-fuel ratio, but it also has the adverse effect of hunting the engine speed due to air-fuel ratio fluctuations.

As a method for detecting such an abnormality in the oxygen sensor 8, it has been proposed to check the responsiveness of the oxygen sensor 8 in a steady state, rather than during transient times such as when the vehicle accelerates or decelerates (California, USA). State CARB
draft).

FIG. 13 is a flowchart illustrating the operation of this method. In FIG.
After determining the basic fuel amount in step S200 in the same manner as the procedure shown in FIG.
52, which is created in advance by a program.

Next, in step S204, the fuel amount is changed stepwise from rich to lean, and then, in step S205, the output signal Vo of the oxygen sensor 8 is read,
In step S206, it is determined whether the output signal Vo is smaller (lean signal) than a predetermined discrimination level Ve. If Vo > Ve, the process proceeds from step S206 to step S207, and the output signal Vo of the oxygen sensor 8 is repeated. When Vo < Ve, the timer activated in step S203 changes the fuel amount in steps and measures the response time Td from when the signal of the oxygen sensor 8 is reversed to the lean side. .

Next, in step S208, this response time T
If d is not larger than a predetermined value Td1, it is determined to be normal; if it is, it is determined to be abnormal, and the result is stored or alarmed as a diagnosis result.

The above operation is performed in the same way when the fuel amount is changed from lean to rich (in this case, To > Te in step S206). Figure 14 shows these operations in a chart, where Figure 14(a) shows the amount of supplied fuel, Figure 14(b) shows the oxygen sensor output,
Further, FIG. 15 is a characteristic diagram relating to the relationship between the temperature and response time of the oxygen sensor 8, as well as abnormality determination.

In the characteristic diagram of FIG. 15, the solid curve a is the characteristic of the fast-responsive, normal oxygen sensor 8;
The broken line curve b indicates a poor response, that is, an abnormal oxygen sensor 8.
It is a characteristic of If the level Td1 is set in advance as the threshold value of the response time Td, the characteristic curve b that shows an abnormal response time due to deterioration at a temperature higher than the temperature at which the oxygen sensor 8 is normally used (for example, 300°C) will be It is determined that there is an abnormality when the operating condition is such that the temperature of the oxygen sensor 8 is approximately 400° C. or lower. Furthermore, a characteristic curve c in which the responsiveness deteriorates is determined to be abnormal regardless of the temperature of the oxygen sensor.

[0015]

[Problem to be Solved by the Invention] Since the conventional oxygen sensor abnormality detection device is configured as described above, the oxygen sensor detects abnormality when the air-fuel ratio is forcibly changed from lean to rich or vice versa. Since the response time of the oxygen sensor 8 is determined based on a certain discrimination value, when the temperature of the oxygen sensor 8 becomes high, it is difficult to determine whether the oxygen sensor 8 is abnormal even if it is abnormal. There was a risk that it would be incorrectly determined to be abnormal.

The temperature of the oxygen sensor depends on the operating conditions (temperature elapsed since starting, rotation speed, load, cooling by running wind, etc.)
The above-mentioned erroneous judgment is difficult to avoid because the value varies greatly depending on the situation.

The present invention was made to solve the above-mentioned problems, and can prevent erroneous determination of normality as abnormality caused by the temperature dependence of the response time of an oxygen sensor, and can operate in a wide temperature range. An object of the present invention is to obtain an oxygen sensor abnormality detection device that enables abnormality determination of an oxygen sensor.

[0018]

[Means for Solving the Problems] An abnormality detection device for an oxygen sensor according to the present invention is provided with a temperature sensor that detects the temperature of the oxygen sensor and inputs the detection signal to a calculation section of a control device. .

[0019]

[Operation] In this invention, the control device corrects the discrimination 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 performs abnormality judgment of the oxygen sensor in a wide temperature range. It acts to prevent misjudgments.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an abnormality detection device for an oxygen sensor according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment. In FIG. 1, the same parts as those in the conventional example shown in FIG. I will mainly discuss the parts that differ from the above.

As is clear from comparing FIG. 1 with FIG. 8, in FIG. 1, the parts indicated by numerals 1 to 10 are the same as in FIG. 8, and the part indicated by numeral 11 is different from FIG. 8. be. That is, the embodiment shown in FIG. 1 is characterized in that a temperature sensor 11 is newly provided in the structure shown in FIG.

This temperature sensor 11 detects the temperature of the oxygen sensor 8, and the detection signal of the temperature sensor 11 is E
The data is sent to the CU10. This ECU10
The internal configuration is shown in FIG. 4, and is similar to the conventional example shown in FIG.
As shown in FIG. 4, the detection signal of the temperature sensor 11 is input. The operation using this temperature sensor 11 will be explained below based on the flowchart shown in FIG. 2 and the characteristic diagram shown in FIG. 3.

The operation shown in the flowchart of FIG. 2 is performed by a microcomputer (CPU,
(consisting of ROM and RAM), first calculates the basic fuel amount in step S200, and then calculates the value Te of the temperature sensor 11 of the oxygen sensor 11 in step S201.
mp is read, and this temperature Tem is read in step S202.
Response time discrimination value Tdo(t
) is determined by a preset calculation formula or table lookup. This response time discrimination value Tdo(t)
As shown in FIG. 3, the characteristics of Temp with respect to the temperature Temp become 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 operations up to step 07 are the same as steps S203 to S207 in FIG. 13 described above as a conventional example, and therefore will be omitted. After measuring the response time Td of the oxygen sensor 8 in step S207 in FIG. 13, it is determined in step S208a whether or not the response time Td is larger than the response time discrimination value Tdo(t) calculated in step S202. If it is small, it is determined to be abnormal, and if it is small, it is determined to be normal.

The same operation as above is performed when the fuel amount is changed stepwise from lean to rich (Vo>Ve in step S206).

Note that when the temperature of the oxygen sensor 8 is lower than the activation temperature, it is necessary to stop the abnormality determination, but this operation is performed in step S2 of the flowchart in FIG.
The response time discrimination value Tdo(
This can be easily done by setting the value of t).

By the way, as specific methods for detecting temperature using the above temperature sensor 11, the following two methods can be considered, for example. The first method is to use a type that has an electric heater built into the oxygen sensor, which has been put into practical use recently.
This method utilizes the temperature dependence of the resistance value of the heater, and if a platinum resistor is used for the heater, it can be used as a good temperature sensor. An example of this characteristic is shown in Figure 5.
An example of the structure is shown in FIGS. 6 and 7.

A specific method for detecting the temperature from the resistance value of the heater is to momentarily stop the power supply to the heater when measuring the temperature, and then measure the resistance value of the heater. Furthermore, it can also be determined from the voltage applied to the heater and the current supplied when the heater is energized.

[0029] The second method is the most common one,
As shown in FIG. 6, a temperature sensor 11 such as a thermistor or platinum is added inside or on the outer periphery of the oxygen sensor 8. 7 is a sectional view of FIG. 6, showing the internal structure of the oxygen sensor 8. As shown in FIG.

As is clear 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,
Exhaust gas A exhausted through the exhaust pipe 6 enters the case 8a through a hole in the case 8a, and the zirconia element 8c (ceramic coated with solid electrolyte) inside the case 8a detects oxygen ions in the exhaust gas A. I have to. An atmosphere side platinum electrode 8d is provided on the inner surface of this zirconia element 8c, and an exhaust side platinum electrode 8e is provided on the outer surface. A heater 8f is inserted at a predetermined distance from the platinum electrode 8d on the atmosphere side. The atmosphere flows between the heater 8f and the atmosphere-side platinum electrode 8d, and the temperature sensor 11 detects the temperature of the heater 8f.

[0031]

As described above, according to the present invention, when an abnormality due to deterioration of an oxygen sensor is determined from the response time when the air-fuel ratio is changed stepwise, the determination time is Since it is configured to change in response to temperature, it is possible to prevent misjudgment (discriminating normal as abnormal) caused by the temperature dependence of the oxygen sensor's response time, and it is also possible to determine abnormality of the oxygen sensor over a wide temperature range. There is.

[Brief explanation of the drawing]

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

FIG. 2 is a flowchart showing the operation flow of the oxygen sensor abnormality detection device of FIG. 1;

FIG. 3 is an abnormality determination characteristic diagram of an oxygen sensor used in the oxygen sensor abnormality detection device of FIG. 1;

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

FIG. 5 is a characteristic diagram of the heater resistance value of the oxygen sensor with a built-in heater used in the oxygen sensor abnormality detection device of FIG. 1;

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

7 is a sectional view showing the configuration of the oxygen sensor of FIG. 6. FIG.

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

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

FIG. 10 is a flowchart showing a calculation procedure of a control device in the oxygen sensor abnormality detection device of FIG. 8;

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 shown in FIG. 8; 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 shown in FIG. 8; FIG.

FIG. 13 is a flowchart showing the flow of operations for detecting an abnormality in an oxygen sensor in the oxygen sensor abnormality detection apparatus shown in FIG. 8;

14 is a waveform diagram of the oxygen sensor in the oxygen sensor abnormality detection device of FIG. 8. FIG.

15 is an abnormality determination characteristic diagram of the oxygen sensor in the oxygen sensor abnormality detection device of FIG. 8. 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 Arithmetic device 51 ROM 52 RAM 53 Drive circuit

Claims (1)

[Claims] Claim 1: An oxygen sensor that detects an air-fuel ratio from engine exhaust gas components, an air flow sensor that detects the intake air amount of the engine, a rotation sensor that detects the engine rotation speed, and supplies fuel to the engine. an injector; a temperature sensor that detects the temperature of the oxygen sensor;
Based on the intake air amount, the rotational speed, and the signal from the oxygen sensor, the air-fuel ratio is feedback corrected using a correction calculation value, and at a predetermined timing, the air-fuel ratio crosses the stoichiometric air-fuel ratio and changes from rich to lean or vice versa. The amount of fuel to the engine is controlled based on the state that changes stepwise, and the response time of the oxygen sensor when the air-fuel ratio changes stepwise when the correction calculation is stopped is detected by the temperature sensor. An abnormality detection device for an oxygen sensor, comprising: a control device that determines that the oxygen sensor is abnormal when the response time exceeds a response time determination value that is changed according to temperature.