JP2532682Y2 - Oxygen sensor heater abnormality diagnosis 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 apparatus for diagnosing an abnormality of a heater of an oxygen sensor for diagnosing whether or not a heater for heating a sensor element of the oxygen sensor is abnormal due to short circuit or disconnection.

[0002]

2. Description of the Related Art An oxygen sensor for detecting the oxygen concentration in exhaust gas is used for controlling the air-fuel ratio of an internal combustion engine. In a cold state (low exhaust temperature), a sensor element of the oxygen sensor is heated by a heater. To set the activation temperature. Further, if the heater is abnormal and the desired heating state is not obtained, and if the heater is continuously used without knowing the desired heating state, the air-fuel ratio control is not performed normally, so that the vehicle continues to travel with an inappropriate exhaust property. Therefore, it has a negative effect on environmental problems.

[0003] Conventionally, an abnormality diagnosis apparatus as described below has been provided. That is, as shown in FIG.
The heater 1 of the oxygen sensor is connected to the FET by the command of the CPU.
(Field effect transistor) It is energized when 2 is ON,
A resistor 3 for current detection is interposed in series with this energizing circuit,
The potential difference between both ends of the resistor 3 is amplified by a differential amplifier circuit 4, A / D converted in a control unit, a current is obtained, and this current is compared with a preset upper limit value and lower limit value. Thereby, the short circuit and the disconnection of the heater 1 are detected. In other words, when the current is equal to or higher than the upper limit value, an excess current is flowing, so it is diagnosed that a short circuit has occurred. Diagnose.

[0004]

By the way, the resistance of the oxygen sensor is usually 4 to 20Ω, and when the battery voltage is within a certain range (for example, V _B = 14 ± 0.3V), the current and the voltage are different. There is a problem that the range in which the self-diagnosis is executed is narrow because the settings are made to correspond one-to-one.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide an apparatus for diagnosing abnormality of a heater of an oxygen sensor having a wide self-diagnosis range.

[0006]

In order to achieve the above-mentioned object, according to the present invention, as shown in FIG. 1, a current detecting resistor inserted in series in a current supply circuit to a heater of an oxygen sensor is provided. A current detecting means (a) for detecting a current of the energizing circuit; and a comparing and diagnosing means for comparing the detected current with an upper limit value and a lower limit value to detect an abnormality due to a short circuit or disconnection of the heater ( b), a power supply voltage detecting means (c) for detecting a power supply voltage of the power supply circuit, and an upper limit value and a lower limit value corresponding to each power supply voltage. And a lower limit value setting means (d).

[0007]

According to the above arrangement, the power supply voltage detecting means detects the power supply voltage of the energizing circuit, and the upper and lower limit value setting means sets an upper limit value and a lower limit value corresponding to each power supply voltage. Then, the current of the current-carrying circuit is detected by current-detecting means having a current-detecting resistor inserted in series with the current-carrying circuit to the heater of the oxygen sensor, and the current detected by the comparative diagnostic means is limited to an upper limit. An abnormality due to a short circuit or disconnection of the heater is detected by comparing the value and the lower limit.

Therefore, even if the power supply voltage fluctuates, the upper and lower limit values are set correspondingly, so that the abnormality diagnosis can be effectively performed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. Note that the system is the same as the conventional example, and the description thereof will be omitted (see FIG. 5). The diagnosis routine is shown in the flowchart of FIG. Step 1 (in the figure, S
Write 1. In the same applies hereinafter), and supplies a power supply voltage V _B,
In step 2, the upper limit is set by the map shown in FIG. 3, and in step 3, the lower limit is set in the same manner. FIG. 3 shows an upper limit value and a lower limit value for each power supply voltage V _B by a current value.

In step 4, the current I detected from the current detecting resistor is input and compared with the upper limit in step 5. If YES (I ≧ upper limit), an excessive current is flowing. , It is determined that the heater is short-circuited, and the routine proceeds to step 8, where it is diagnosed that the heater is abnormal. Step 5
If the result is NO, the process proceeds to step 6. In step 6, the current I is compared with the lower limit value. If YES (I ≦ lower limit value), the current is too small, so that it is considered that the heater is disconnected, and the process proceeds to step 8 and is abnormal. And make a diagnosis. If the result of the comparison in step 6 is NO, the process proceeds to step 7, where the diagnosis is made as normal and the routine ends. That is, the current is an appropriate value between the lower limit and the upper limit.

Here, step 1 corresponds to power supply voltage detecting means, steps 2 and 3 correspond to upper and lower limit value setting means,
Step 4 corresponds to the current detection means, and steps 5 to 8 correspond to the comparative diagnosis means. FIG. 4 shows a map for converting the upper limit value and the lower limit value shown in FIG. 3 into voltage values. This is because the value detected by the energizing circuit is theoretically the current value, but in practice, it is detected as a voltage value, so that the detected value is not directly converted to a current value, but is directly compared and diagnosed. In order to serve.

[0012]

[Effect of the invention] As described above, according to the invention,
Since the power supply voltage is detected and the upper and lower limits are set accordingly, there is no need to narrow the range of diagnosis in anticipation of fluctuations in the power supply voltage as in the past, and effective diagnosis is possible. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a configuration of the present invention.

FIG. 2 is a flowchart showing a diagnosis routine.

FIG. 3 is a diagram showing upper and lower limit values for each power supply voltage.

FIG. 4 is a diagram for converting a current value to a voltage value.

FIG. 5 System diagram

FIG. 6 is a diagram showing a conventional problem.

[Explanation of symbols]

 1 Heater 3 Resistance

Claims (1)

(57) [Scope of request for utility model registration] A current detection means for detecting a current of the current supply circuit, wherein a current detection resistor is provided in series with a current supply circuit to a heater of the oxygen sensor; Power supply voltage detection means for detecting a power supply voltage of the energizing circuit in a device for diagnosing abnormality of a heater of an oxygen sensor, comprising: a comparison diagnosis means for detecting an abnormality due to a short circuit or disconnection of the heater by comparing the value with a lower limit value. And an upper / lower limit value setting means for setting an upper limit value and a lower limit value according to each power supply voltage, respectively.