JPH0118378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control method for an oxygen sensor equipped with a heater.

Oxygen sensors include those that use an oxygen ion conductive solid electrolyte to detect oxygen concentration using the principle of an oxygen concentration battery, and those that use an oxide semiconductor to detect oxygen concentration based on changes in its resistance. There are things etc. For these oxygen sensors, there is a temperature range in which they have the best operating characteristics depending on their configuration, so many oxygen sensors are equipped with a heater to ensure stable operation. Japanese Unexamined Patent Publication 1973-
Publication No. 13396). Examples of batteries that apply the principle of oxygen concentration batteries include those that use a crucible-type solid electrolyte and those that use a solid electrolyte in the form of a thin film.

FIG. 1 shows an example of a temperature control system in a conventional oxygen sensor, and the oxygen sensor 1 is equipped with a heater 2 for heating. One end of the heater 2 is grounded, and the other end is connected to a power source 4 via a contact 3a of a relay 3. On the other hand, relay switch 5
is connected to the power source 4 and grounded via the coil 3b of the relay 3, so that opening and closing of the relay 3 can be controlled. In this case, the oxygen sensor 1 is fixed to the exhaust pipe of a vehicle internal combustion engine so as to be able to measure the oxygen concentration in exhaust gas. Further, the power source 4 is a battery. Furthermore, the relay switch 5 has a terminal 5a for inputting a key switch signal.
and a terminal 5b into which the output signal of the temperature detection element 6 that detects the temperature of the oxygen sensor 1 is input. Then, the relay switch 5 turns on only when the key switch signal is on and the temperature of the oxygen sensor 1 is below a predetermined temperature, turning on the relay 3 and supplying the power source 4 to the heater 2. supply Further, when the temperature of the oxygen sensor 1 exceeds a predetermined temperature, the relay switch 5 is turned off, the relay 3 is turned off, and the power supply 4 to the heater 2 is cut off. The temperature was maintained around a preset temperature.

However, in the conventional case described above, the heater 2 is heated near the set temperature for the oxygen sensor 1.
Since the power source 4 is supplied/cut off to the oxygen sensor 1, when the vehicle is running in such a state that the temperature of the oxygen sensor 1 is close to the set temperature, hunting occurs around the set temperature, and the temperature is around the set temperature. The power supply 4 is being supplied and cut off extremely frequently, which may significantly shorten the life of the opening/closing mechanism such as the relay 3, and at the same time, the temperature rise and fall of the oxygen sensor 1 is repeated quite frequently. Therefore, the oxygen sensor 1 may deteriorate prematurely, and furthermore, the durability of the heater 2 may be reduced.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to be able to perform good temperature control of an oxygen sensor with a simple and inexpensive configuration, and to supply power to a heater for heating the oxygen sensor.
It is possible to extend the life of the opening/closing mechanism that performs the shutoff, and in addition, it is possible to prevent frequent temperature rises and falls caused by the oxygen sensor heater, thereby avoiding early deterioration, and improving the durability of the heater. An object of the present invention is to provide a method for controlling the temperature of an oxygen sensor.

In an oxygen sensor equipped with a heater for heating, when supplying or cutting off power to the heater, the power is cut off to the heater when the temperature of the oxygen sensor exceeds a first predetermined temperature. and when the temperature of the oxygen sensor reaches a second predetermined temperature set lower than the first predetermined temperature, power is supplied to the heater, and the power supply and the heater are connected. The present invention is characterized in that a hysteresis characteristic is provided at the intermittent timing to control the temperature of the oxygen sensor.

Examples of the present invention will be described in more detail below.

FIG. 2 is a temperature control system diagram of an oxygen sensor according to an embodiment of the present invention.
1 has a structure equipped with a heater 12 for heating. One end of the heater 12 is grounded, and the other end is connected to a power source 14 via a contact 13a of a switch (relay in the illustrated example) 13. On the other hand, the temperature sensor 15 is connected to the coil 13b of the switch 13.
It is connected to the power supply 14 via the power source 14 and grounded via an internal temperature detection calculation mechanism, so that opening and closing of the switch 13 can be controlled. Further, the temperature detector 15 has a terminal 15a into which a key switch signal is input, and a terminal 15b into which an output signal of a temperature detection element 16 that detects the temperature of the oxygen sensor 11 is input. And temperature sensor 1
5, when the key switch is turned off, no control signal is generated regardless of the magnitude of the output signal from the temperature detection element 16, and the switch 13 is kept open. On the other hand, when the key switch is on, such as when starting or running the vehicle, different control signals are generated depending on the magnitude of the output signal from the temperature detection element 16 to control the opening and closing of the switch 13.

Therefore, when the key switch is on, oxygen is supplied and cut off to the heater 12 based on the output signal from the temperature detection element 16, which changes in accordance with the temperature of the oxygen sensor 11. The manner in which the temperature control of the sensor 11 is executed will be described. Therefore,
When the vehicle starts driving, the oxygen sensor 11 is heated by the heater 12 and further heated by the exhaust gas, and as the temperature of the oxygen sensor 11 rises, the output signal from the temperature detection element 16 also changes. While this output signal continues to be input to the temperature detector 15, when the temperature of the oxygen sensor ₁₁ exceeds a preset first predetermined temperature T1, the temperature detector 15 generates a first signal. and open the contact 13a of the switch 13 to cut off the heater 12 and the power source 14,
On the contrary, when the temperature of the oxygen sensor 11 decreases and reaches a second predetermined temperature _T2 set lower than the first predetermined temperature _T1 , the temperature detector 15 generates a second signal, The contact 13a of the switch 13 is closed to connect the heater 12 and the power source 14. That is, as shown in FIG. 3, based on the operation of the temperature detector 15 and the switch 13, a first predetermined temperature T ₁ is set to cut off the power supply 14 to the heater 12, and The second predetermined temperature T ₂ at which the heater 12 is supplied is made different from the second predetermined temperature T 2 , so that the supply/cutoff of the power source 14 to the heater 12 has hysteresis characteristics.

FIG. 4 is a temperature control circuit diagram of an oxygen sensor showing a more specific example of the present invention, in which 11 is an oxygen sensor, 12 is a heater, 13 is a switch, in this case a relay type switch, and 14 is a power supply, and a diode is connected to the coil 13b of the switch 13.
D ₁ are connected in parallel, and the coil 1
One end of the transistor 3b is connected to the collector of the transistor 17, and the emitter of the transistor 17 is grounded.

On the other hand, the operational amplifier 18 is operated by a constant voltage power supply _Vc , and this constant voltage power supply _Vc is supplied through the terminal 15a only when the key switch is on. Further, an output signal from the temperature detection element 16 that detects the temperature of the oxygen sensor 11 is applied to the negative terminal of the operational amplifier 18 via the terminal 15b. In this case, as the temperature detection element 16, a thermistor whose resistance value changes depending on the temperature, a thermocouple whose output voltage changes, etc. can be used. Even when using a thermistor, a separate thermistor is used for the oxygen sensor 11. In addition to providing the element, a heater 1 constituting the oxygen sensor 11 is provided.
2. Changes in resistance value due to temperature of electrodes, solid electrolytes, etc. can also be used as they are as a thermistor element. The output voltage V s is inputted to the negative terminal of the operational amplifier 18 as an output voltage V _s that changes in response to changes in the temperature of the oxygen sensor 11 . Therefore,
For example, when using a thermistor, the thermistor and a predetermined value resistor are connected in series, a constant voltage is applied to both ends, and the output voltage V _s is extracted from the junction as a divided voltage of both resistors. Therefore, a change in the resistance value of the thermistor due to temperature can be extracted as a change in the output voltage _Vs. In addition,
The resistance change due to temperature of the thermistor has opposite characteristics when using the heater 12 or an electrode as the thermistor element and when using a solid electrolyte, so it is necessary to take this into account. An example will be described in which a temperature detection element 16 is used in which the output voltage V _s increases as the temperature of the sensor 11 increases.

Further, a voltage V _p obtained by internally dividing the reference voltage V _t and the output terminal voltage V ₀ by the resistors R ₁ and R ₂ is applied to the positive terminal of the operational amplifier 18 . That is, V _p =(R ₁ ·V ₀ +R ₂ ·V _t )/(R ₁ +R ₂ )...(1) is applied. Furthermore, the output terminal voltage V ₀ is the resistance
It is input to the base side of the transistor 17 via _R3 . Note that _R4 is a resistor for stabilizing circuit operation.

So, if the key switch is off,
As mentioned above, the operational amplifier 18 is connected to a constant voltage power supply V _c
is not supplied, so the output terminal voltage V ₀ =0,
Since the transistor 17 is in a non-conductive state, the contact 13a of the switch 13 is always open, and the power source 14 is cut off to the heater 12.

Furthermore, when the key switch is on, the constant voltage power supply V _c is supplied to the operational amplifier 18 . Then, when the temperature of the oxygen sensor 11 is low and the output voltage V _s from the temperature detection element 16 is low, V _s <
V _p , and the output voltage V ₀ at this time is V ₀ = V _c , so the voltage V _p is calculated from equation (1) above, V _p = (R ₁ · V _c · R ₂ · V _t ) / (R ₁ + R ₂ ) ...(2). At this time, the transistor 17
is in a conductive state, so the coil 13b of the switch 13
The power supply 14 is energized and excited, and the contact 13a of the switch 13 is closed, so that the power supply 14 for the heater 12 is turned on and excited.
4 to raise the temperature of the oxygen sensor 11.

Next, as the temperature of the oxygen sensor 11 rises, the output voltage V _s from the temperature detection element 16 increases accordingly, but when the temperature of the oxygen sensor 11 reaches the first predetermined temperature T ₁ (see FIG. 3), When the output voltage V _s exceeds the positive terminal voltage
When V _p becomes larger than V p and V _s > V _p = (R ₁ · V _c + R ₂ · V _t ) / (R ₁ + R ₂ ) ...(3), the output terminal voltage V _c becomes V ₀ =0,
The positive terminal voltage V _p at this time is determined from the above equation (1) as follows: V _p =R ₂ ·V _t /(R ₁ +R ₂ ) (4). In this state, the transistor 17
becomes non-conductive, and at this time the first signal is generated and sent to the switch 13, the power supply 14 to the coil 13b of the switch 13 is cut off and demagnetized, and the contact 13a is opened. As a result, the power supply 14 to the heater 12 is cut off.

Next, the temperature of the oxygen sensor 11 decreases again,
The output voltage V _s from the temperature detection element 16 becomes lower,
When the second predetermined temperature T ₂ (see FIG. 3), which is set lower than the first predetermined temperature T ₁ , is reached, the output voltage V _s becomes smaller than the positive terminal voltage V _p . , V _s < V _p = R ₂ · V _t / (R ₁ + R ₂ ) ...(5), the output terminal voltage V ₀ becomes V ₀ = V _c , and the positive terminal voltage V _p becomes V again. _p = (R ₁ · V _c + R ₂ · V _t ) / (R ₁ + R ₂ ) ...At the same time as returning to (2)', the transistor 17 becomes conductive, and at this time, the second signal is generated. This is then sent to the switch 13, the power supply 14 is supplied to the coil 13b of the switch 13, and the coil 13b is energized, the contact 13a is closed and the heater 12 is turned on.
The power supply 14 is supplied again to generate heat, and the temperature of the oxygen sensor 11 increases.

In this way, in the circuit shown in FIG. 4, the output voltage V _s from the temperature detection element 16, which changes in response to the temperature change of the oxygen sensor 11, is the voltage at the positive terminal of the operational amplifier 8, V _p ; V _p =( When the voltage becomes larger than R ₁・V _c +R ₂・V _t )/(R ₁ +R ₂ ), the power supply 1
4 is blocked. After that, when the output voltage V _s becomes smaller than the positive terminal voltage V _p of the operational amplifier 18; V _p = R ₂ · V _t / (R ₁ + R ₂ ), the power supply 1 is
4 is supplied. Therefore, in the characteristics shown in FIG. 3, the output voltage V _s from the temperature detection element 16 at the first predetermined temperature T ₁ at which the power supply 14 is cut off for the heater 12 is V _p = (R ₁ · V _c + _R2・_Vt )/
(R ₁ +R ₂ ), and the output voltage V _s from the temperature detection element 16 at the second predetermined temperature T ₂ at which the power supply 14 is supplied to the heater 12 is V _p
= R ₂ · V _t / (R ₁ + R ₂ ), so
The values are different from each other, and a hysteresis characteristic can be provided to the supply/cutoff of the power supply 14 to the heater 12.

FIG. 5 shows the relationship between the temperature of the oxygen sensor 11 and the opening/closing state of the switch 13 using specific numerical values.
On the other hand, the first predetermined temperature T ₁ at which the power supply 14 is cut off corresponds to approximately 750°C, and the second predetermined temperature T ₂ at which the power supply 14 is supplied to the heater 12 corresponds to approximately 550°C. Therefore, when the temperature of the oxygen sensor element 11 exceeds approximately 750°C, the power supply 14 is cut off and the heater 12 no longer generates heat.
1 can be prevented from excessive temperature rise. On the other hand, in the process of decreasing the temperature of the oxygen sensor 11, when the temperature reaches approximately 550°C, the power supply 14 is supplied and the heater 12 generates heat, so the temperature of the oxygen sensor 11 is raised again to reach the appropriate temperature. can be held.

Therefore, as shown in FIG. 5, when the temperature of the oxygen sensor 11 rises to about 750°C, the switch 1
When the temperature of the oxygen sensor 11 drops to about 550°C, the contact 13a of the oxygen sensor 11 is closed and the power supply 14 is supplied again. sensor 1
Contact 1 of switch 13 due to minute fluctuations in temperature of switch 13
3a can be prevented from opening and closing each time, and the contact 1
Since the frequency of opening and closing of 3a can be reduced,
It is possible to lengthen the durable life of the contact 13a, and at the same time, it is possible to avoid frequent repetition of heat generation and stoppage of the heater 12, thereby preventing deterioration caused by frequent repeated application of thermal stress to the oxygen sensor 11. It can be prevented, and heater 1
2. Durability can be improved. In other words, for example, if the power source 14 is supplied and cut off to the heater 12 at the same temperature (assuming 650°C) as in the conventional case, if the temperature of the oxygen sensor 11 is around 650°C, If the vehicle is driven with a low temperature, the contact 13a will open and close extremely frequently even when there is a slight change in temperature, which will shorten the life of the contact 13a, etc., and also cause the heater 1 to
2 will be repeated extremely frequently, reducing the durability of the heater 12, and the temperature of the oxygen sensor 11 will be repeatedly raised and lowered, causing the oxygen This will cause early deterioration of the sensor 11.

In the embodiments described above, the oxygen sensor 11 is not limited to one using an oxygen ion conductive solid electrolyte.

As described above, according to the present invention, when controlling the temperature of an oxygen sensor equipped with a heater, the temperature of the oxygen sensor can be well controlled with a simple and inexpensive configuration, and the temperature of the atmosphere to be measured increases. It is possible to maintain the temperature of the oxygen sensor within an appropriate range even when the temperature drops, and since the temperature of the oxygen sensor is different when power is supplied or cut off to the heater, the oxygen It is possible to eliminate the frequent opening and closing operations of the switches installed between the heater for heating the sensor and the power supply, and it is possible to prevent shortening of the life of the switches. Since it is possible to prevent temperature rises and falls, it is possible to prevent early deterioration of the oxygen sensor, and it is also possible to bring about very excellent effects such as being able to improve the durability of the heater.

[Brief explanation of drawings]

Fig. 1 is a temperature control system diagram of a conventional oxygen sensor, Fig. 2 is a temperature control system diagram of an oxygen sensor in an embodiment of the present invention, and Fig. 3 is a diagram of temperature and opening/closing of an oxygen sensor in an embodiment of the present invention. FIG. 4 is a temperature control circuit diagram of an oxygen sensor in an embodiment of the present invention, and FIG. 5 is a diagram specifically showing the relationship between the temperature of the oxygen sensor and the open/close state of the switch. FIG. 11...Oxygen sensor, 12...Heater, 13
... Switch, 14 ... Power supply, 15 ... Temperature detector.

Claims (1)

[Claims] 1. A method for controlling the temperature of an oxygen sensor attached to a vehicle by opening/closing a switch interposed between a heater for heating the oxygen sensor provided in the oxygen sensor and a power source, While detecting the temperature of the oxygen sensor with a temperature detector,
When the temperature exceeds a first predetermined temperature, the temperature sensor generates a first signal, the first signal is sent to the switch to open the switch, and the temperature exceeds the first predetermined temperature. When a second predetermined temperature lower than the first predetermined temperature is reached, a second signal is generated from the temperature sensor, and this second signal is sent to the switch to close the switch. A temperature control method for an oxygen sensor, characterized in that: