JP2546395B2 - Oxygen sensor heater control failure diagnosis device - Google Patents

Description

Description: TECHNICAL FIELD The present invention is used for controlling a heater of an oxygen sensor, and is used for diagnosing a failure of a heater of an oxygen sensor, a transistor, or an analog signal / digital signal converter. The present invention relates to a heater control failure diagnosis device.

[Conventional technology]

In the heater control of the oxygen sensor, the heater current is detected as an analog signal, converted by an analog signal / digital signal converter, and the digital signal is taken into a microprocessor for feedback control (for example, JP-A-60-125).
553 publication).

[Problems to be Solved by the Invention]

However, in the conventional device described above, when the analog signal / digital signal converter is out of order, the heater control is performed with incorrect data even if the transistor is normal.
There is a problem that the control performance deteriorates.

Therefore, it is an object of the present invention to determine whether the analog signal / digital signal converter is normal or abnormal.

[Means for solving the problem]

Therefore, according to the present invention, as shown in FIG. 1, a heater for heating an oxygen sensor, a transistor for controlling a current flowing through the heater, a current detection means for detecting the current flowing through the heater as an analog signal, and the analog. A heater control device for an oxygen sensor, comprising: an analog signal / digital signal converter for converting a signal into a digital signal; a signal capturing means for capturing the digital signal; and a control means for controlling the transistor according to the captured digital signal. When the heater is off and the digital signal is equal to or larger than a first predetermined value, and when the heater is on for a predetermined time or longer and the digital signal is equal to or larger than a second predetermined value that is larger than the first predetermined value. It is characterized in that it is provided with a judging means for judging an abnormality when at least one of time and time is satisfied. There is provided a heater control malfunction diagnosis apparatus of the unit sensor.

[Action]

The current value flowing through the heater of the oxygen sensor detected by the current detecting means is converted into a digital signal by the analog signal / digital signal converter, and the digital signal is taken into the judging means by the signal taking means. The digital signal is compared with a predetermined value. An abnormality is determined based on the comparison result and the ON / OFF signal of the control means. That is, the current value flowing through this heater when the heater of the oxygen sensor is off and the current value flowing through this heater after the heater of the oxygen sensor has been on for a predetermined time are taken in, and these current values are compared with the corresponding predetermined values. When at least one of the comparison results does not satisfy the condition, it is determined to be abnormal.

〔Example〕

 The present invention will be described below with reference to embodiments shown in the drawings.

(First Embodiment) In FIG. 2, a titania oxygen sensor with a heater is used as an oxygen sensor 9 for detecting the oxygen concentration in the engine exhaust gas. The heater 2 includes a battery 10, a heater 2, and a transistor 3. , The current detection resistor 4 is connected in series in this order.

A resistor R1 is connected to both ends of the current detection resistor 4 to detect the voltage applied to the current detection resistor 4. The diode 8 is connected to a 5V constant voltage power supply,
The resistor R3 plays a role of protecting the analog signal / digital signal converter 7, and the resistor R3 causes the short circuit of the load for a long time to prevent the operational amplifier 5 from operating.
Plays a role in preventing damage. The resistors R1 and R2 and the operational amplifier 5 form a differential amplifier circuit.

The output terminal of the microprocessor 1 is connected to the transistor 3 through the inverter TRO, and the input terminal is connected to the analog signal / digital signal converter 7. The analog signal / digital signal converter 7 is connected to the differential amplifier circuit, and has a titania resistance of the oxygen sensor 9.
It is also connected to Hr.

Next, the operation will be described. The transistor 1 is turned on by the microprocessor 1, and the heater 2 for heating the oxygen sensor 9 is driven by the signal thereof. According to the oxygen sensor temperature-heater resistance value characteristic diagram of FIG. 5, the changing heater current is extracted as an analog voltage by the current detection resistor 4 and amplified by the operational amplifier 5. The reason why the amplification reference is set to a constant voltage of 5V instead of the ground is that the ground potentials of the power system ground 6 and the operational amplifier 5 may be different.

The analog voltage amplified by the operational amplifier 5 is converted into a digital value by the analog signal / digital signal converter 7 and then taken into the microprocessor 1, and the analog signal / digital signal converted value corresponding to the base current is corrected and output to the transistor 3. , The current of the heater 2 is controlled.

The conventional analog signal / digital signal conversion is only performed after the delay time after the heater is turned on and the influence of the inrush current disappears. However, in the present invention, the analog signal / digital signal conversion is further performed after the heater is turned off. This is to detect whether the transistor 3 and the analog signal / digital signal converter 7 are normal or abnormal.

FIG. 3A is a flowchart of the entire heater control. In step 401, which is a signal capturing means, an analog signal /
The digital signal converted by the digital signal converter 7 is taken into the memory of the microprocessor 1. Step 402 is a processing routine after the analog signal / digital signal conversion from step 101 to step 124, which will be described in detail later.

If the heater normal flag is on (step 124) in step 403, the process proceeds to step 404, and if the same flag is off (step 122), the process returns to step 401. Step 40
In calculating the heater current for 4, the control target temperature (for example, 750
℃) near the current value C and ADIHT (heater current analog signal / digital signal conversion value is corrected from 5V reference to ground reference) to calculate the duty ratio, the control means of step 405 to the duty ratio In response, the signal is output to the transistor 3 to control the heater 2 and the process returns to step 401.

FIG. 3B is a flowchart showing details of step 402. In step 101, it is determined whether the heater 2 is on or off. When it is off, in step 102, ADIHT is compared with 0 corresponding to the first predetermined value, and if not 0, an analog signal /
Since the digital signal converter 7 or the transistor 3 is abnormal, the heater off error flag in step 103 is turned on. If 0, the same flag in step 104 is turned off.

Next, in step 101, when the heater is turned on, it is compared in step 105 whether ADIHT when the heater is turned on is equal to or more than an arbitrary current value A (for example, a current value corresponding to 1500 ° C.), and if it is smaller than 1500 ° C. Since the temperature is higher, it is determined to be abnormal, and the heater on error flag in step 107 is turned on. If it is A or higher, it is 1500 ° C. or lower, so the same flag in step 106 is turned off.

Next, at step 108, if ADIHT is less than or equal to a predetermined current value B (current value corresponding to a very low temperature) corresponding to the second predetermined value, even if the current is continuously energized, the heater 2 and the current detection resistor 4 are overloaded. Therefore, the continuous heater flag in step 109 is turned on, and the heater 2 is kept on while the flag is on. However, if ADIHT is larger than B, there is a concern that the heater 2 and the current detection resistor 4 will be overloaded.

If the heater can be energized continuously, step 11
The heater continuous ON time is monitored by the count CHTON of 0, and if TMAX or more in step 111, then the heater is continuously turned on.
From the figure, it is abnormal because the temperature of the heater has not reached the vicinity of the control target temperature even though the current continues to flow to the heater for the TMAX time, and the continuous heater on error flag of step 115 is turned on.

However, if it is smaller than TMAX, in steps 112 and 113,
Determine whether ADIHT has decreased to the current value C,
When the current value C is reached, it is determined in step 114 whether CHTON at that time is within the normal range. If it is within the normal range, the transistor 3, the analog signal / digital signal converter 7, and the heater 2 of the oxygen sensor 9 are determined. The continuous heater on error flag in step 116 is turned off, including that including normal.

If CHTON is out of the normal range, the same flag in step 115 is turned on. Then, the above step 103, step 107,
If at least one of the flags in step 115 is turned on, it is determined to be abnormal in steps 119, 120, and 121, the heater normal flag in step 122 is turned off, and feedback is given in step 123. Abnormal processing such as stopping the control and lighting a warning is performed.

If all of the above steps 103, 107 and 115 are off, the flag is turned on at step 124.

As described above, duty control is performed when the heater resistance value corresponds to an extremely low temperature, but when the resistance value reaches a certain resistance value, the heater characteristics can be checked by continuously energizing and monitoring the temperature rise of the heater. For example, it is possible to detect improper assembly, misassembly, or deterioration of the oxygen sensor.

Second Example Next, a second example will be described. In FIG. 6, step 102 to step 107 and step 117 to step 124 in FIG. 3B are the same, and therefore illustration and description thereof will be omitted.
If the heater 2 is turned on in step 101 and ADIHT is determined to be equal to or less than the predetermined current value B in step 201, the continuous heater ON time is monitored by the count CHTON in step 202, and electricity is supplied for a fixed time (1≤CHTON≤T3). To do. When CHTON reaches arbitrary time T3 in step 203, when it is determined in step 204 that ADIHT is not within the control target temperature range (I1≤ADIHT≤I2),
The continuous heater on error flag in step 205 is turned on, and it is determined that there is an abnormality.

In this embodiment, the time to enter the feedback control of the heater 2 of the oxygen sensor 9 is delayed compared to the first embodiment, but the load of software is lightened because it is not necessary to determine the timer overflow or the like.

Third Embodiment Next, a third embodiment will be described. In FIG. 7, Step 102 to Step 107 and Step 117 to Step 124 in FIG. 3B are the same, and therefore illustration and description thereof will be omitted.

In this embodiment, instead of forcibly energizing the heater 2 of the oxygen sensor 9 continuously, the energization time of the heater 2 during duty control is accumulated, and when a predetermined time is reached, ADIHT is inspected.

This will be described below with reference to FIG. When the heater 2 is turned on in step 101, ADIHT is equal to or less than the predetermined current value B and step 301
If it is determined in step 302, the heater energization time during duty control is accumulated in step 302 (CDUSUM), and in step 303 CDUSU
When M reaches the predetermined time T4, the judgment values I3 and I4 of ADIHT are calculated from the characteristic diagram of FIG. 4 and CDUSUM in step 304. If it is not within this range (I3 ≦ ADIHT ≦ I4), step 307 is turned on. Turn on the duty error flag to determine an abnormality.

〔The invention's effect〕

As described above, the present invention has an excellent effect that not only the failure of the heater and the transistor but also the failure of the analog signal / digital signal converter can be detected, and the heater control with excellent control performance can be obtained. .

[Brief description of drawings]

FIG. 1 is a block diagram of the present invention, FIG. 2 is an electric circuit diagram showing a first embodiment of the device of the present invention, FIG. 3A is a flow chart of the entire heater control, and FIG. 3B is an explanation of the operation of the first embodiment. 4 is a flow chart of the heater energization time-resistance value characteristic diagram, FIG. 5 is an oxygen sensor temperature-heater resistance value characteristic diagram, FIG. 6 is a flow chart for explaining the operation of the second embodiment, and FIG. 9 is a flowchart for explaining the operation of the third embodiment. 1 ... Microprocessor, 2 ... Heater, 3 ... Transistor, 4 ... Current detection resistor, 5 ... Operational amplifier, 7 ... Analog signal / digital signal converter, 9 ... Oxygen sensor.

Claims (1)

(57) [Claims] 1. A heater for heating an oxygen sensor, a transistor for controlling a current flowing through the heater, a current detecting means for detecting a current flowing through the heater as an analog signal, and an analog for converting the analog signal into a digital signal. In a heater control device for an oxygen sensor, comprising: a signal / digital signal converter, a signal capturing means for capturing the digital signal, and a control means for controlling the transistor according to the captured digital signal, the heater is off. And at least one of when the digital signal is a first predetermined value or more and when the heater is on for a predetermined time or more and the digital signal is a second predetermined value or more larger than the first predetermined value. Oxygen sensor heater control failure characterized by having a determination means for determining abnormality when the oxygen sensor is activated Cross-sectional devices.