JPH0219727Y2 - - Google Patents

Description

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

The oxygen concentration and air-fuel ratio of the exhaust gas of an internal combustion engine have a good correlation in the air-fuel ratio that is larger than the stoichiometric air-fuel ratio, that is, in the region of lean mixture, so by measuring the oxygen concentration of the exhaust gas in this region, , the exhaust gas air-fuel ratio can be detected accurately. 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 certain current is passed between the two electrodes in such a lean sensor, oxygen can be moved in one direction through the electrolyte, but the diffusion resistance of the micropores causes less oxygen to be delivered than the oxygen delivery capacity of the air permeability measuring electrode. By covering this permeability measuring electrode with a layer, it is possible to maintain its current at approximately a certain value in 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 2, and energization of the heater is controlled by a switch.

FIG. 1 shows a conventional lean sensor heating device, in which 1 is a lean sensor, in which a bottomed circular oxygen ion-conducting solid electrolyte made of, for example, zirconia is connected to its inner and outer surfaces with 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 inside the element 2 and is connected via a contact 4a of a heater electromagnetic switch 4 to a storage battery 5 as a power source. An excitation coil 4b of the heater switch 4 is connected to a storage battery 5 via an ignition switch 6.

Now, when the ignition switch 6 is closed, the switch 4
Since the excitation coil 4b is energized and closes the contact 4a, the heater 3 is supplied with power and heats the sensor element 2. With this configuration, the sensor element 2 is always heated while the engine is operating, that is, while the ignition switch 6 is closed, so that the sensor element 2 is heated to the appropriate temperature during high engine load operation or high vehicle speed when the exhaust gas temperature is high. (650-800°C) or higher, which may cause deterioration of the sensor element. However, if the heater is de-energized even during short-term high-load or high-speed operation, the temperature of the sensor element will drop below the appropriate temperature, resulting in Immediately after the transition from to low-speed operation, the sensor element is not at an appropriate temperature, so the air-fuel ratio of the exhaust gas cannot be accurately detected.

The purpose of the present invention is to prevent the sensor element from overheating and increase its durability, and to maintain the sensor element within an appropriate temperature range so that the air-fuel ratio of exhaust gas can be stably detected. Therefore, according to the present invention,
A switching device is provided to cut off the power supply circuit of the heater when a high engine load state or a high vehicle speed state continues for a set time or more.

An embodiment of the invention is shown in FIG.
Parts corresponding to the figures are given the same reference numerals. Excitation coil 4b of heater switch 4 is connected to storage battery 5 via relay switch 10. This relay switch 10 includes an NPN switching transistor 11 whose collector-emitter circuit is connected to an excitation coil 4b, and a base of this transistor 11.
An NPN transistor 12 with a collector-emitter circuit connected to an emitter circuit, the bases of these transistors 11 and 12, and one end 15 of a constant voltage power supply.
It includes voltage stabilizing elements 13 and 14 each consisting of a Zener diode and a resistor inserted between the two. The base of the transistor 11 is connected to the open/close signal output terminal 16 of the ignition switch via the resistance of the voltage stabilizing element 13, and the base of the transistor 12 is connected to the time counter 17 via the resistance of the voltage stabilizing element 14. has been done. This time counter 17 counts the pulse signals applied from the logic circuit 18, and when a specific count value, ie, time, is exceeded, it applies an on signal to the base of the transistor 12. Logic circuit 18 is OR circuit 2
1, one input end of which is a vehicle speed signal output end 2.
The other input terminal is connected to the output terminal of the AND circuit 23. Two input ends of this AND circuit 23 are connected to an engine speed signal output end 24 and an intake pipe pressure signal output end 25, respectively. For example, an ON signal appears at the output end 24 at an engine speed of 4000 rpm or more, and an ON signal appears at the output end 25, for example, at an intake pipe pressure of -100 mHg or less.

Now, when the engine starts operating, an ON signal is given to the open/close signal output terminal 16 of the closed ignition switch, so the open/close transistor 11 becomes conductive, and the excitation coil 4b of the heater switch 4 is connected to the storage battery 5.
Since the contact 4a is closed, the heater 3 of the lean sensor 1 is energized and the sensor element 2 is heated. When the engine is in a high load state (engine speed is 4000 rpm or more and intake pipe pressure is -100 mHg or less) or the vehicle speed is high (120 km/h or more), the OR circuit 21 generates an ON signal. time counter 17
When the output of the OR circuit 21 continues beyond the set time, an on signal is given to the base of the control transistor 12, so this transistor 12 becomes conductive, makes the switching transistor 11 non-conductive, and turns off the heater 3. to sever.

In this embodiment, the lean sensor 1 is used as the oxygen sensor, but other oxygen sensors whose electromotive force exhibits Z characteristics at the stoichiometric air-fuel ratio may be used.

Thus, according to the present invention, only when the high load state of the engine that produces high temperature exhaust gas or the high vehicle speed state continues for a set time or more, the power to the heater 3 is immediately cut off, so that the sensor element 2 is turned off. Overheating is prevented. On the other hand, if the duration of these states is less than the set time, the sensor element 2 continues to be energized, which prevents the sensor element 2 from dropping below the appropriate temperature. Since this is only carried out for a short time, the sensor element will not be overheated due to its large heat capacity. In this way, it is possible to accurately detect the air-fuel ratio in exhaust gas by keeping the temperature of the sensor element within an appropriate temperature range while preventing deterioration of the sensor element due to overheating.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram of a conventional lean sensor heating device, and FIG. 2 is a connection diagram of an embodiment of the present invention. 1...Lean sensor, 2...Sensor element, 3...
...Electric heater, 4...Heater switch, 10...Relay switch, 16...Ignition switch open/close signal output terminal, 17...Time counter, 18...Logic circuit,
22...Vehicle connection signal output end, 24...Engine speed signal output end, 25...Intake pipe pressure signal output end.

Claims (1)

[Scope of utility model registration request] A heating control device for an oxygen sensor that controls a heater built into an oxygen sensor that is installed in the exhaust system of an internal combustion engine and detects the oxygen concentration in exhaust gas, when the engine is in a high load state or a high vehicle speed state for a set period of time or more. 1. A heating control device for an oxygen sensor, characterized in that a switching device is provided to cut off a power supply circuit of a heater.