JPH0249567Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating control device for an oxygen sensor that is installed in an exhaust pipe of an internal combustion engine and is heated by an electric heater to generate an output proportional to the oxygen concentration of exhaust gas.

The oxygen concentration of the exhaust gas of an internal combustion engine and the air-fuel ratio have a good correlation in the air-fuel ratio greater than the stoichiometric air-fuel ratio, that is, in the region of a lean mixture.
By measuring the oxygen concentration of the exhaust gas in this region, the exhaust gas air-fuel ratio can be accurately detected. As a sensor for measuring the exhaust gas oxygen concentration in such a region (hereinafter referred to as a lean sensor), an air permeability measurement electrode is provided on the side of the exhaust gas to be measured, and a reference gas having a known oxygen concentration is provided on the side of the atmosphere, for example. There is a bottomed cylindrical sensor consisting of a breathable counter electrode and a solid electrolyte, such as stabilized zirconia, between the electrodes. When a current is passed between the electrodes in such a lean sensor, oxygen can be moved in one direction through the electrolyte, but the microporous diffusion resistance layer transports less oxygen than the oxygen delivery capacity of the air permeability measuring electrode. By coating this permeability measuring electrode with , it is possible to maintain its current at approximately a certain value over a certain applied voltage range. Since this current value changes linearly almost in proportion to the oxygen concentration, the oxygen concentration can be continuously detected from changes in this current value. On the other hand, in order for this lean sensor to output a current value proportional to the oxygen concentration of exhaust gas with a constant applied voltage, it is necessary to heat the element temperature of the lean sensor to approximately 650°C or higher and maintain it in an active state. . For this purpose, an electric heater is provided within the cylindrical sensor element, and energization of the heater is controlled by a switch. However, if the energization duration of the heater becomes unnecessarily long, the sensor may deteriorate due to overheating. For example, while the engine is warming up and a rich mixture is being supplied, there is no need for the lean sensor to function, but conventional devices use the ignition switch as the switch, so when the engine is running, This ignition switch is always closed, regardless of engine temperature, so the heater is always energized. Therefore, a sensor that is heated even when heating is unnecessary will deteriorate and have reduced durability.

In view of these problems, the present invention was developed with the aim of preventing unnecessary heating of the sensor and improving the durability of the sensor. A heating control device for an oxygen sensor that detects the oxygen concentration in exhaust gas, comprising an engine temperature detection means that detects the temperature of an internal combustion engine, and a power supply to the electric heater until the engine temperature reaches a predetermined temperature. The gist of the present invention is a heating control device for an oxygen sensor, comprising: a means for inhibiting power supply for inhibiting power supply; and a heating control device for an oxygen sensor.

To explain the embodiment of the present invention with reference to the drawings, 1 is a lean sensor, in which a bottomed cylindrical oxygen ion conductive solid electrolyte made of, for example, zirconia is coated on its inner and outer surfaces with air permeable thin film electrodes (not shown). and forms the sensor element 2. Both electrodes are connected to a constant voltage power source. In order to heat the sensor element 2, an electric heater 3 is provided within the sensor element 2 and is connected via a contact 4a of a heater switch 4 to a storage battery 5 as a power source. Excitation coil 4b of heater switch 4 is connected to storage battery 5 via relay switch 10 including a transistor. In other words, the relay switch 10
The emitter collector circuit of the NPN transistor 11 is connected to the storage battery 5 in series with the excitation coil 4b. The base of the transistor 11 is connected to one end 12 of a constant voltage power supply via a voltage stabilizing element consisting of a Zener diode and a resistor.
Logic circuit 1 consisting of AND circuit 14 and OR circuit 15
It is connected to the output terminal of the AND circuit 14 of No. 3.
One input terminal of the AND circuit 14 is connected to the ignition switch open/close signal output terminal 16, and the other input terminal is connected to the ignition switch open/close signal output terminal 16.
It is connected to the output end of the OR circuit 15. this
Two input terminals of the OR circuit 15 are connected to an engine cooling water temperature sensor output terminal 17 and an oil temperature sensor output terminal 18. Both sensors are designed to issue an on signal when the water or oil temperature is, for example, 40°C or higher.

Now, when you close the ignition switch and start the engine,
An on signal is given to the AND circuit 14 from the output terminal 16, but if both the engine cooling water temperature and oil temperature are still below 40°C, no on signal is given to the other input terminal of the AND circuit 14. , the transistor 11 is not conductive and therefore the heater 3 is not energized either. After starting, the engine is warmed up to, for example, 40℃.
At this point, an ON signal appears at one or both of the output terminals 17 and 18, so the AND circuit 14 generates an ON signal at the output terminal, and the transistor 11
conduction. Since the contact 4a of the heater switch 4 is now closed, the heater 3 is energized and heats the sensor element 2.

Even if the engine is once stopped, if the engine is started again while the engine is still warm, that is, while the water or oil temperature is 40° C. or higher, the sensor element 2 will be heated immediately. Of course, below this temperature, the sensor element 2 will not be heated immediately even if the engine is restarted.

Thus, according to this embodiment, the heater of the lean sensor is energized according to the warm-up state of the engine,
The durability of the sensor element can be increased by preventing the sensor element from being heated during the warm-up process when there is no need to detect the exhaust gas air-fuel ratio. Furthermore, not supplying electricity to the heater during the warm-up process reduces the current consumption of the storage battery, prevents its voltage from dropping, lengthens its usage time before recharging, and prevents its deterioration. As explained above, in the oxygen sensor heating control device of the present invention, power supply to the electric heater is prohibited until the engine temperature reaches a predetermined temperature. Accordingly, when the oxygen sensor is in the warm-up process where there is no need to detect the oxygen concentration in the exhaust gas, heating of the oxygen sensor can be prevented and the durability of the sensor can be improved.

[Brief explanation of the drawing]

The figure is a connection diagram of an embodiment of the present invention. 1...Lean sensor, 2...Sensor element, 3...
...Electric heater, 4...Heater switch, 5...Storage battery, 10...Relay switch, 13...Logic circuit,
16...Ignition switch open/close signal output terminal, 17...
Water temperature sensor output end, 18...Oil temperature sensor output end.

Claims (1)

[Scope of Claim for Utility Model Registration] A heating control device for an oxygen sensor installed in the exhaust pipe of an internal combustion engine and heated by an electric heater to detect the oxygen concentration in exhaust gas, the engine detecting the temperature of the internal combustion engine. A heating control device for an oxygen sensor, comprising: temperature detection means; and power supply prohibition means for prohibiting power supply to the electric heater until the engine temperature reaches a predetermined temperature.