JPH11344465A - Trouble diagnostic apparatus of heater for sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the trouble diagnosing accuracy of a heater when the supply of power to the heater for a sensor is performed by controlling the duty factor. SOLUTION: When collector voltage V does not drop to a level lower than a threshold value V0 and is a value out of a predetermined range, even if the predetermined period TO corresponding to the change delay time of collector voltage V is elapsed at each time when the base signal VB of the transistor of a heater control circuit transfers from off to on, the times becoming out of the predetermined range during a period of ON signals of several times are integrated and, when the integrated time reaches a predetermined time (CO), a heater is judged to be abnormal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for diagnosing failure of a heater for a sensor.

[0002]

2. Description of the Related Art Generally, a catalyst device is disposed in an exhaust system of a vehicle engine for purifying exhaust gas, and an oxygen sensor (for example, a zirconia type) for detecting feedback information of air-fuel ratio control is provided upstream of the catalyst device. Oxygen sensor). Since the oxygen sensor does not function unless the temperature exceeds a predetermined temperature, it is necessary to quickly increase the sensor temperature at the time of cold start of the engine, and since the temperature dependence of the sensor output value is large, the temperature of the sensor element is reduced. It is necessary to perform fine control so as to always maintain the appropriate temperature. Therefore, conventionally, a heater is provided in addition to the sensor, and the sensor temperature is controlled to a target temperature by adjusting the power supplied to the heater. Power supply to the heater for controlling the sensor temperature is generally turned on / off by a switching circuit using a transistor, for example.
It is performed with off control. In addition, simple on / off control increases the fluctuation range of the sensor temperature.
For example, as disclosed in JP-A-3-189350, power supply to a heater is controlled by a duty signal, and the sensor temperature is finely controlled by adjusting the duty ratio.

The device disclosed in Japanese Patent Application Laid-Open No. 3-189350 is based on the assumption that the resistance value of a heater for temperature control in an oxygen sensor indicates the sensor temperature, and the heater resistance value becomes a predetermined target resistance value. A heater control device that controls the power supplied to the heater and updates and stores the target resistance value so as to eliminate the effects of individual differences and changes over time. At the time of replacement, the stored value of the target resistance becomes an abnormal value far from the required value, and an abnormality occurs in the sensor temperature and the like due to the abnormality in the target resistance. In order to cope with the abnormality such as the sensor temperature that occurs, when the state where the power supplied to the oxygen heater is out of the predetermined range continues for a predetermined period, it is determined that the target resistance value is abnormal, and the sensor temperature or the like is abnormal. Always it has been described that to be able to cope.

[0004]

By the way, when performing a failure diagnosis of a heater for controlling the temperature of a sensor such as an oxygen sensor,
In a device that controls the heater temperature by simply turning on and off the power supply to the heater, for example, when the base signal of a transistor (grounded emitter) shifts from off to on, the change delay time for each inversion of the base signal The heater is determined to be normal if the collector voltage shows a change to fall to a certain level after a predetermined time (for example, 2 seconds) that is long enough to eliminate noise and eliminate noise. If the collector voltage has not fallen to a certain level, it can be determined that there is an abnormality.

However, in duty control of the power supply to the heater so as to more finely control the sensor temperature, a base signal applied to, for example, a transistor of the power supply control circuit shifts from, for example, off to on for a predetermined time. When the failure of the heater is diagnosed by observing the change in the collector voltage after the elapse of the time, the base signal is inverted in a very short time, so that it is sufficient to eliminate the change delay time and the noise. Time cannot be taken, and it may not be possible to distinguish it from noise.

Therefore, it is an object to improve the accuracy of heater failure diagnosis when power is supplied to the sensor heater by duty control.

[0007]

SUMMARY OF THE INVENTION A failure detection device for a sensor heater according to the present invention sets a supply period and a non-supply period of power per unit time and controls a supply power by a duty signal for adjusting a ratio between the two periods. A failure diagnosis device for a heater for a sensor to be controlled, comprising: detection means for detecting a value relating to power supplied to the heater; and an output of the detection means, the power supply being provided in one of a power supply period and a non-supply period in a duty signal. Abnormality determining means for integrating a time when the detected value is out of a predetermined range and determining that the heater is abnormal when the integrated time is equal to or longer than a predetermined time. The value related to the supply power is a collector voltage or the like when the power supply is adjusted by controlling the base signal of the transistor. The sensor is, for example, an oxygen sensor that detects the oxygen concentration in the engine exhaust gas. In this case, a heater is arranged near the oxygen sensor element.

The power supply to the heater is controlled by a duty signal. Then, for example, the collector voltage of the transistor is detected as a value related to the power supplied by the heater, and the power supply period (O
During one of the N signal generation period) and the non-supply period (OFF signal generation period), the time during which the detected value is outside the predetermined range is integrated, and if the integrated time exceeds the predetermined time, it is determined that the heater is abnormal. You. If the heater is normal, the duty signal shifts from OFF to ON or turns OFF.
By transitioning from ON to ON, for example, the detected value of the collector voltage falls or rises and becomes a stable value within a predetermined range. However, if the value is not normal, the detected value becomes a predetermined value during the ON signal period or the OFF signal period. An out-of-range condition occurs. However, even if the detected value deviates from the predetermined range during the period of the ON signal or the period of the OFF signal, the heater alone does not always have an abnormality. Since the duty signal is inverted in a short time, it is difficult to distinguish it from noise, and a value outside a predetermined range may be detected due to noise. Therefore, when the time when the detected value is out of the predetermined range is equal to or longer than the predetermined time, noise is eliminated by determining that the heater is abnormal for the first time. However, since the period of the ON signal or the period of the OFF signal in the duty signal is short, it is determined in a single period of the ON signal or the OFF signal whether the time during which the detection value is outside the predetermined range is equal to or longer than a predetermined time. Can not usually. Therefore, the period of the ON signal or the OFF
In one of the signal periods, the time when the detected value is out of the predetermined range is integrated, and when the integrated time is equal to or longer than the predetermined time, it is determined that the abnormality is abnormal. Diagnosis becomes possible.

The power supply period (the ON signal generation period) and the non-supply period (OF
For a predetermined period after the transition from one of the F signal generation periods to the other, it is preferable to prohibit the accumulation of time for abnormality determination.
In particular, it is preferable that the predetermined period in which the integration is prohibited be set to a time longer than the delay in changing the detected value when the duty signal is shifted from one of the supply period and the non-supply period to the other. The change in the power supplied to the heater when the duty signal is inverted has a delay time, and if the heater is normal, the power changes to a certain level after the change delay time. Therefore, the detected value during the change delay time is outside the above-mentioned predetermined range regardless of whether the heater is normal or abnormal, and if the time is accumulated, an erroneous determination of the heater abnormality is generated. Therefore, the integration is prohibited for a predetermined period after the inversion of the duty signal, and thereby the determination accuracy is improved. In particular, by making the integration prohibition period longer than the change delay time, erroneous determinations caused by the change delay time can be completely eliminated.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the entire structure of an engine provided with a failure diagnosis device to which the present invention is applied.

In FIG. 1, 1 is an engine main body, and 2 is a combustion chamber thereof. An intake port 3 and an exhaust port 4 are opened in the combustion chamber 2, and an intake valve 5 and an exhaust valve 6 are arranged at openings of the intake port 3 and the exhaust port 4 to the combustion chamber 2. An intake passage 7 is connected to an inlet of the intake port 3, and an exhaust passage 8 is connected to an outlet of the exhaust port 4. In the intake passage 7, an air cleaner 9, an air flow sensor 10, a throttle valve 11, a surge tank 12, and a fuel injection valve 1 are arranged in this order from the upstream side.
3 is provided, and a bypass passage 14 for bypassing the throttle valve 11 is provided. A bypass valve (ISC valve) 15 for controlling the idle speed is provided in the middle of the passage 14. A crank angle sensor 16 for detecting a crank angle signal is provided at a predetermined position of the engine body 1, and a water temperature sensor 17 for detecting the temperature of the engine cooling water is provided. A catalyst device 18 for purifying exhaust gas is provided in the middle of the exhaust passage 8, and an oxygen sensor 19 is provided upstream thereof. The oxygen sensor 19 has a built-in electric resistance type heater 20 shown in FIG. 2 near the sensor element. The heater 20 is connected to the ground side of the transistor whose emitter is grounded, and the power supply is controlled by a duty signal applied to the base of the transistor.

The detection signals of the air flow sensor 10, the crank angle sensor 16, the water temperature sensor 17, and the oxygen sensor 19 are input to an ECU (engine control unit) 21 as control information. The ECU 21 performs a fuel injection control process and an ISC control process based on the control information, and performs a power supply control process to the heater 20 built in the oxygen sensor 19. Is output to the fuel injection valve 13, the ISC valve 15, and the heater 20, respectively.

The ECU 21 performs a process of diagnosing a failure of the heater 20 built in the oxygen sensor 19. Basically, this failure diagnosis process detects the collector voltage of the transistor of the heater control circuit every time the duty signal for controlling the power supply to the heater 20 shifts from OFF to ON. The time out of the predetermined range is calculated, the time calculated in the period of the plurality of ON signals is integrated, and if the integrated time is equal to or longer than the predetermined time, it is determined that the heater 20 is abnormal, and the warning light 22 Is turned on, and a heater abnormality is stored in the ECU 21.

[0015] In the process of fault diagnosis of the heater 20, as shown in FIG. 3, each time the base signal V _B of the transistor of the heater control circuit is shifted to ON from OFF, ON collector voltage V change delay time (e.g., about 5 ms) collector voltage V when the corresponding predetermined time period T _o has elapsed see whether falls to a lower level than the threshold V _o (predetermined range). If the collector voltage V has not fallen to a level lower than V _o even after a predetermined period T _o has elapsed after the base signal V _B has shifted from OFF to ON, during the ON signal period, the collector voltage V There subtracting the diagnostic counter C for a time not lower than the threshold V _o level. In FIG. 3,... Indicate the period of the ON signal. In this example, the collector voltage V changes from the power supply voltage (12 V) to a level lower than V _o (ground voltage) during the period, but the collector voltage V does not decrease as indicated by the solid line during the period (normal). (A broken state is indicated by a broken line). in this case,
The diagnostic counter C sets the initial value to a time sufficient for noise elimination (at least 500 msec or more, preferably 2 seconds, for example).
Set ec), first collector voltage V in the above-mentioned period is subtracted time not to a level lower than the threshold V _o. Then, since the counter value is a period of one ON signal is not 0 (zero), further subtracts the time the collector voltage V does not become lower level than the threshold V _o in the period of the ON signal, thus , The counter value is 0
When it becomes (zero), it is determined that the heater is abnormal.

[0016] Figure 4 is a flow chart for executing the processing of the fault diagnosis, when started, first, a timer T is set to 0 (zero) at step S1, sets the diagnostic counter C to the initial value C _o, Next, step S2
In inputs based signals V _B and the collector voltage V of heater control transistor. Then, in step S3,
Base signal V _B to see whether the state of the ON signal of the duty, by adding the timer T in step S4 if ON signal, the process proceeds to step S6. Also, the term OFF signals not based signal V _B is ON signal is determined in step S3, and a timer T to 0 (zero) at step S5, it returns to step S2.

In step S6, it is checked whether the timer T is _{equal to} or longer than a predetermined time To. Then, the timer T is T _o
The process proceeds to step S9 without anything as it does not reach the, on the other hand, when the timer T is greater than or equal to T _o step S
Proceed to 7.

In step S7, it is determined whether or not the collector voltage V is lower than the threshold value V _O. If the collector voltage V is lower than V _O (within the predetermined range), the process proceeds to step S9 without doing anything. On the other hand, if the collector voltage V is not lower than V _O (out of the predetermined range), the process first proceeds to step S9. In S8, the diagnostic counter C is decremented, and then the process proceeds to Step S9.

In step S9, the diagnostic counter C is set to 0.
See if (zero). If the diagnostic counter C has not become 0, the process returns to step S2,
Steps S2 to S8 are repeated. Then, step S9
When the counter C becomes 0 (zero), step S1
If 0, it is determined that the heater is abnormal, the warning lamp 22 is turned on, and the ECU 21 stores the heater abnormality.

In the above example, the collector voltage is detected as a value relating to the power supplied to the heater for the purpose of diagnosing the heater failure. However, the embodiment of the present invention is not limited to this.

Further, in the above example, the heater failure diagnosis is performed based on the detection value of the duty signal during the ON signal period.
The heater failure diagnosis may be performed based on the detection value during the period of the F signal.

The present invention is also applicable to failure diagnosis of various sensor heaters in addition to the oxygen sensor heater in the engine.

[0023]

According to the present invention, it is possible to improve the accuracy of heater failure diagnosis when power is supplied to the sensor heater by duty control.

[Brief description of the drawings]

FIG. 1 is an overall structural diagram of an engine according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a heater.

FIG. 3 is a time chart showing a heater failure diagnosis process.

FIG. 4 is a flowchart for executing a heater failure diagnosis process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 8 Exhaust passage 19 Oxygen sensor 20 Heater 21 ECU (Engine control unit) 22 Warning light

Claims (4)

[Claims] 1. A failure diagnosis apparatus for a heater for a sensor, wherein a supply period and a non-supply period of power per unit time are set and a supply signal is controlled by a duty signal for adjusting a ratio between the two periods. Detecting means for detecting a value related to the supplied power of the power supply, receiving an output of the detecting means, integrating a time when the detected value is out of a predetermined range in one of a power supply period and a non-supply period in the duty signal, and An abnormality determining means for determining that the heater is abnormal when the integrated time is equal to or longer than a predetermined time; 2. The sensor according to claim 1, wherein the sensor is an oxygen sensor for detecting an oxygen concentration in engine exhaust gas, and the heater is disposed near the oxygen sensor element.
A failure diagnosis device for a heater for a sensor according to the above. 3. The sensor according to claim 1, wherein integration of the time for abnormality determination is prohibited during a predetermined period after transition from one of a power supply period and a non-supply period in the duty signal to the other. Heater failure diagnosis device. 4. The sensor according to claim 3, wherein the predetermined period is set to be longer than a change delay time of the detection value when transitioning from one of a power supply period and a non-supply period in the duty signal to the other. Diagnosis device for heaters.