JPH04134063U - Oxygen sensor heater abnormality diagnosis device - Google Patents

Abstract

(57) [Summary] [Purpose] To enable diagnosis of heater short circuits and disconnections in response to fluctuations in power supply voltage. [Structure] A resistor 3 for current detection is inserted in series in the energizing circuit to the heater 1 of the oxygen sensor, and the current I of the energizing circuit is detected, and the detected current I is used as an upper limit value and a lower limit value. By comparison, an abnormality due to a short circuit or disconnection of the heater 1 is diagnosed. At this time, the power supply voltage V _B is detected and upper and lower limit values are set according to the power supply voltage V _B so that fluctuations in the power supply voltage V _B can be coped with. This achieves the above objectives and enables effective abnormality diagnosis.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention prevents short-circuiting or disconnection of the heater for heating the sensor element of the oxygen sensor. Diagnosis of oxygen sensor heater abnormalities to determine whether an abnormality has occurred due to Regarding the disconnection device.

0002

[Conventional technology]

Oxygen sensors that detect the oxygen concentration in exhaust gas are used to control the air-fuel ratio of internal combustion engines. However, when it is cold (low exhaust temperature), the sensor element of the oxygen sensor is heated by a heater. The temperature is then set to the activation temperature. Also, if an abnormality occurs in this heater and the desired heating state cannot be obtained, it may be turned off. If you continue to use it without knowing this, the air-fuel ratio control will not be performed properly, resulting in poor exhaust characteristics. Since the vehicle continues to run properly, it has a negative impact on environmental issues.

0003 Therefore, abnormality diagnosis devices such as those shown below have been conventionally provided. That is, as shown in FIG. 5, the heater 1 of the oxygen sensor When T (field effect transistor) 2 is turned on, it is energized; A detection resistor 3 is inserted in series, and the potential difference between both ends of this resistor 3 is sent to a differential amplifier circuit 4. The current is amplified, A/D converted within the control unit, and the current is By comparing with preset upper and lower limit values, short circuits and It is designed to detect disconnections. In other words, when the current is above the upper limit, excessive Since current is flowing, it is diagnosed that there is a short circuit, and the current is below the lower limit value. If this happens, the current is too low, so the diagnosis is that the wire is disconnected.

0004

[Problem that the idea aims to solve]

By the way, the resistance of the oxygen sensor is usually 4 to 20Ω, and the resistance is set so that the current and voltage correspond one to one within a certain range of battery voltage (for example, V _B = 14±0.3V). Therefore, there was a problem that the range in which self-diagnosis could be executed was narrow.

[0005] In view of the above-mentioned conventional problems, this invention is an oxygen sensor with a wide range of self-diagnosis. The purpose of the present invention is to provide an abnormality diagnosis device for a heater.

[0006]

[Means to solve the problem]

In order to achieve the above object, the present invention has developed a heating system for an oxygen sensor, as shown in Fig. 1. The energizing circuit has a resistor for detecting current inserted in series in the energizing circuit to the energizing circuit. a current detection means (a) for detecting the current of Comparative diagnostic means (b) for comparing and detecting an abnormality due to short circuit or disconnection of the heater; ), in the oxygen sensor heater abnormality diagnostic device having: A power supply voltage detection means (c) that detects the power supply voltage, and upper and lower values corresponding to each power supply voltage. Upper and lower limit value setting means (d) for setting respective limit values are provided.

[0007]

[Effect]

According to the above configuration, the power supply voltage detection means detects the power supply voltage of the energized circuit. and set the upper and lower limits according to each power supply voltage using the upper and lower limit value setting means. Set. A current detection circuit is connected in series to the energizing circuit to the oxygen sensor heater. The current in the current-carrying circuit is detected by the current detecting means having a resistance, and the comparative diagnosis means The detected current is compared with the upper limit value and the lower limit value to determine whether the heater is short-circuited or detects abnormalities due to wire breaks.

[0008] Therefore, even if the power supply voltage fluctuates, the upper and lower limits are set accordingly. Effective abnormality diagnosis becomes possible.

[0009]

【Example】

Embodiments of the present invention will be described below with reference to FIGS. 2 to 4. The system is the same as the conventional example, so its explanation will be omitted (see FIG. 5). The diagnostic routine is shown in the flowchart of FIG. In step 1 (indicated as S1 in the figure; the same applies hereinafter), the power supply voltage V _B is input, in step 2, the upper limit value is set using the map shown in Fig. 3, and in step 3, the lower limit value Set. In FIG. 3, the upper limit value and lower limit value for each power supply voltage V _B are shown as current values.

0010 In step 4, input the current I detected from the current detection resistor, and in step 5 Compare this with the upper limit value, and if YES (I≧upper limit value), excessive current is flowing. Therefore, assume that the heater is short-circuited, proceed to step 8, and diagnose it as abnormal. put down. Further, if the comparison in step 5 is NO, proceed to step 6. In step 6, the current I is compared with the lower limit value, and if YES (I≦lower limit value), Since the current is too low, assume that the heater is disconnected and proceed to step 8 to check if there is a problem. It is diagnosed as normal. Also, if the comparison in step 6 is NO, step 7 Proceed to , diagnose it as normal, and exit this routine. That is, the current is , is an appropriate value between the lower limit and the upper limit.

[0011] Here, step 1 corresponds to the power supply voltage detection means, and steps 2 and 3 are the upper and lower limit values. It corresponds to the setting means, step 4 corresponds to the current detection means, and steps 5 to 8 correspond to the comparison means. Corresponds to diagnostic means. Figure 4 shows a map for converting the upper and lower limits shown in Figure 3 into voltage values. It shows. This means that the value detected by the current-carrying circuit is theoretically the current value. However, in practice, it is detected as a voltage value, so it is not possible to convert the detected value to a current value. This is to directly provide a comparative diagnosis.

0012

[Effect of the idea]

As explained above, according to the present invention, the power supply voltage is detected and raised accordingly. Since the limit value and lower limit value are set, diagnosis can be performed in anticipation of power supply voltage fluctuations, as in the past. There is no need to narrow the scope of diagnosis, and effective diagnosis becomes possible. be able to.

[Brief explanation of drawings]

[Figure 1] Functional block diagram showing the configuration of the present invention

[Figure 2] Flowchart showing the diagnostic routine

[Figure 3] Diagram showing upper and lower limit values for each power supply voltage

[Figure 4] Diagram of converting current value to voltage value

[Figure 5] System diagram

[Figure 6] Diagram showing conventional problems

[Explanation of symbols]

1 Heater 3 Resistance

Claims (1)

[Scope of utility model registration request] 1. A current detection means for detecting the current of the energization circuit, the current detection means having a current detection resistor interposed in series with the energization circuit for the heater of the oxygen sensor, and an upper limit for the detected current. power supply voltage detection means for detecting the power supply voltage of the current-carrying circuit; 1. An abnormality diagnosis device for a heater of an oxygen sensor, comprising: and upper and lower limit value setting means for respectively setting upper and lower limit values according to each power supply voltage.