JPS646695B2 - - 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 for inputting a full throttle signal. Then, the relay switch 5 turns on only when the key switch signal is on and the full throttle signal is off, turning on the relay 3 and switching the power supply 4 to the heater 2.
supply. Further, when the full throttle signal is on (fully open state), 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.

In such a conventional temperature control system, the reason why the power supply 4 is not supplied to the heater 2 is as follows.
This occurs only when the full throttle signal is on, that is, when the throttle valve is fully open. On the other hand, as the vehicle speed increases, the load on the internal combustion engine also increases, and accordingly, the exhaust gas temperature also increases, and the temperature of the oxygen sensor also increases. In this case, the throttle valve will be fully open and the power source 4 will no longer be supplied to the heater 2, as shown in Figure 2, although this will vary depending on the road conditions and driving style. As the temperature of the oxygen sensor continues to rise as the exhaust gas temperature rises, for example, there is a possibility that the temperature will significantly exceed the appropriate operating temperature range of 550 to 850°C for an oxygen sensor using an oxygen ion conductive solid electrolyte. . Furthermore, as mentioned above, even at low vehicle speeds, the exhaust gas temperature rises during high-load operation such as when climbing a hill, and the power supply 4 continues to be supplied to the heater 2 until just before the throttle valve is fully opened. There was a possibility that the oxygen sensor could become overheated beyond the proper operating temperature range. Another disadvantage is that if the oxygen sensor is overheated, it may cause early deterioration.

On the other hand, the oxygen sensor 1 can be measured by directly providing a temperature measuring means such as a thermocouple on the oxygen sensor 1, or by utilizing the change in resistance value due to the temperature of the heater 2.
It is conceivable to detect the temperature of the heater 2 and supply/cut off power to the heater 2 at a set temperature for the oxygen sensor, but the supply/cut off of power near the set temperature is extremely frequent. Because this process is carried out over a period of time, there is a risk of significantly shortening the life of the opening/closing mechanism such as the relay 3, and at the same time, since the temperature rise and fall of the oxygen sensor 1 is repeated quite frequently, there is a risk of premature deterioration of the oxygen sensor 1. There were still problems such as:

SUMMARY OF THE INVENTION An object of the present invention is to provide a temperature control method for an oxygen sensor that eliminates the drawbacks of the prior art described above and that can prevent excessive temperature rise of the oxygen sensor with a simple and inexpensive configuration.

In an oxygen sensor equipped with a heater for heating, the vehicle speed is set to a first predetermined speed when power is supplied to or cut off to the heater based on a signal that changes depending on the driving state of the vehicle. power is cut off to the heater when the vehicle speed exceeds the first predetermined speed, and power is supplied to the heater when the vehicle speed reaches a second predetermined speed that is set lower than the first predetermined speed. The oxygen sensor is characterized in that the temperature of the oxygen sensor is controlled by providing a hysteresis characteristic to the intermittent timing of the power supply and the heater.

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

FIG. 3 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 vehicle speed detector 15 is connected to the coil 13b of the switch 13.
It is connected to the power source 14 via an internal vehicle speed detection calculation mechanism, and is grounded via an internal vehicle speed detection calculation mechanism, so that opening and closing of the switch 13 can be controlled. Furthermore, the vehicle speed detector 15 has a terminal 15a for inputting a key switch signal, and a terminal 15b for inputting a vehicle speed signal from a normal speedometer S which generates a voltage proportional to the speed of the vehicle. and,
When the key switch is turned off, the vehicle speed detector 15 does not generate an output signal regardless of the magnitude of the vehicle speed signal, and keeps the switch 13 open. On the other hand, when the key switch is on, such as when starting or driving the vehicle,
Different output signals are generated depending on the magnitude of the vehicle speed signal to control opening and closing of the switch 13.

Therefore, when the key switch is on, the power source 14 is supplied to the heater 12 based on a vehicle speed signal that changes in accordance with the vehicle speed.
A mode of controlling the temperature of the oxygen sensor 11 by shutting it off will be described. Therefore, as the vehicle speed increases after the vehicle starts driving, the vehicle speed signal also changes, but while this vehicle speed signal continues to be input to the vehicle speed detector 15, the vehicle speed changes to the preset first predetermined speed v ₁ When the vehicle speed exceeds the first signal, the first signal is generated from the vehicle speed detector 15, and the contact 13a of the switch 13 is opened to cut off the heater 12 and the power source 14. Conversely, when the vehicle speed decreases and the first signal is When a second predetermined speed _v2 , which is set lower than the first predetermined speed _v1 , is reached, the vehicle speed detector 15 generates a second signal, the contact 13a of the switch 13 is closed, and the heater 12 is closed. Connect it to the power supply 14. That is, the fourth
As shown in the figure, vehicle speed detector 15 and switch 1
Based on the operation of step 3, the power source 1 is connected to the heater 12.
a first predetermined speed v ₁ for cutting off the heater 1;
The second predetermined speed v ₂ at which the power source 14 is supplied to the heater 12 is set to be different from the second predetermined speed v 2 at which the power source 14 is supplied to the heater 12 so that the supply/cutoff of the power source 14 to the heater 12 has hysteresis characteristics.

FIG. 5 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 1 is connected to the coil 13b of the switch 13.
6 are connected in parallel, and the coil 13
One end of transistor b is connected to the collector side of transistor 17, and the emitter side of 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, a signal from a speedometer S that generates a voltage V _s according to the vehicle speed is applied to the negative terminal of the operational amplifier 18, and a reference voltage V _t and an output terminal voltage V ₀ are applied to the positive terminal. Resistance R ₁ ,
A voltage V _p internally divided by R ₂ is applied. 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 . When the vehicle speed is 0 or low and the output voltage V _s from the speedometer S is low, V _s < V _p , and the output terminal voltage V ₀ at this time is V ₀ = V _c . , the voltage V _p is obtained from the above equation (1) as follows: 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.

Furthermore, as the vehicle speed increases, the output voltage V _s from the speedometer S increases accordingly, but when the vehicle speed exceeds the first predetermined speed V ₁ ,
When the output voltage V _s becomes larger than the positive terminal voltage 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 ₀ becomes V ₀ =0, and the positive terminal voltage V _p at this time is obtained from the above formula (1), V _p = R ₂ · V _t / (R ₁ + R ₂ )...(4) becomes. 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, when the vehicle speed shifts to the low speed side again, the output voltage V _s from the speedometer S becomes low, and the second predetermined speed V ₂ set lower than the first predetermined speed V ₁ is reached. , when the output voltage V _s becomes smaller than the positive terminal voltage V _p and becomes 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 returns to V _p = (R ₁ · V _c + R ₂ · V _t ) / (R ₁ + R ₂ )...(2)′ At the same time, the transistor 17 becomes conductive, and at this time a second signal is generated, which is 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, and the contact 13a is turned on. When closed, the heater 12
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. 5, the output voltage V _s from the speedometer S according to the vehicle speed is the positive terminal voltage V _p of the operational amplifier 18; V _p = (R ₁ · V _c + R ₂ · V _t )/(R ₁ + R ₂ ), power supply 1 is applied to heater 12.
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. 4, the output voltage V _s from the speedometer S at the first predetermined speed V ₁ at which the power supply 14 is cut off to the heater 12 is V _p = (R ₁ · V _c + R ₂・V _t )/
(R ₁ +R ₂ ), and the output voltage V _s from the speedometer S at the second predetermined speed v ₂ of supplying the power source 14 to the heater 12 is V _p =
It corresponds to R ₂ · V _t / (R ₁ + R ₂ ), so
Each has a different value, and a hysteresis characteristic can be provided to the supply/cutoff of the power supply 14 to the heater 12.

FIG. 6 shows an example of the relationship between the vehicle speed and the opening/closing state of the switch 13 using concrete numerical values _. is equivalent to 80km/h,
The second predetermined speed v ₂ supplied to the power source 14 for the heater 12 corresponds to 75 km/h. Therefore, when the vehicle speed exceeds 80 km/h, the power supply 14 is cut off and the heater 12 no longer generates heat, so that the temperature of the oxygen sensor 11 varies to a certain extent as shown in FIG. The temperature is heated by the exhaust gas of the internal combustion engine, and an excessive rise in temperature of the oxygen sensor 11 can be prevented compared to the conventional case shown in FIG. In the illustrated example, the vehicle speed is
When the speed exceeds 80 km/h, the oxygen sensor 11 is simply heated by the exhaust gas and can be maintained at an appropriate temperature. On the other hand, when the vehicle speed decreases, the exhaust gas temperature also decreases, so the temperature of the oxygen sensor 11 also decreases as shown in FIG.
When the vehicle speed reaches 75 km/h, the power supply 14 is supplied and the heater 12 generates heat, so the oxygen sensor 1
1 can be maintained at an appropriate temperature.

Therefore, as shown in FIG. 7, the vehicle speed at which the contact 13a of the switch 13 opens and the power supply 14 is cut off is 80 km/h, and the contact 13a closes and the power supply 14 is supplied again. Since the vehicle speed is 75 km/h, the contact 13a of the switch 13 can be prevented from opening and closing every time due to minute fluctuations in the vehicle speed, and the frequency of opening and closing of the contact 13a can be reduced. It is possible to extend the durability life, 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. At the same time, the durability of the heater 12 can be improved. In other words, for example, as in the conventional case, the power supply 14 to the heater 12 is supplied and cut off at the same vehicle speed (temporarily 80 km/h).
In the case of h), if the vehicle is running at a constant speed of around 80 km/h, the contact 13a will open and close extremely frequently even when there is a slight change in vehicle speed, which will shorten the life of the contact 13a, etc. Since the heating and stopping of the heater 12 are repeated extremely frequently, the durability of the heater 12 is reduced, and the temperature of the oxygen sensor 11 is repeatedly raised and lowered quite frequently. , this will cause early deterioration of the oxygen sensor 11.

In the embodiments described above, the oxygen sensor 11 is not limited to one using an oxygen ion conductive solid electrolyte. Note that when detecting the oxygen concentration in the exhaust gas of a vehicle internal combustion engine, the temperature of the oxygen sensor is generally lower than the value shown in Figure 7 when the fuel is cut off, but when the fuel is cut off, air-fuel ratio feedback control is required. Since this is not done, there is no problem.

As described above, according to the present invention, when controlling the temperature of an oxygen sensor equipped with a heater, it is possible to prevent an excessive temperature rise of the oxygen sensor with a simple and inexpensive configuration, and to prevent the temperature of the atmosphere to be measured from rising. It is possible to maintain the oxygen sensor within the appropriate temperature range even when the oxygen It has very excellent effects such as being able to prevent early deterioration of the sensor and also improving 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 graph showing the relationship between the vehicle speed and the temperature of the oxygen sensor in the conventional example, and Fig. 3 is a diagram of the oxygen sensor in an embodiment of the present invention. A temperature control system diagram, FIG. 4 is an explanatory diagram showing the relationship between vehicle speed and the open/close state of the switch in an embodiment of the present invention,
Fig. 5 is a temperature control circuit diagram of an oxygen sensor in an embodiment of the present invention, Fig. 6 is an explanatory diagram showing the relationship between vehicle speed and the open/closed state of the switch, and Fig. 7 is a diagram showing the relationship between vehicle speed and the temperature of the oxygen sensor. It is a graph showing the relationship between 11... Oxygen sensor, 12... Heater, 13... Switch, 14... Power supply, 15... Vehicle speed 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 vehicle speed of the vehicle with a vehicle speed detector, when the vehicle speed exceeds a first predetermined speed, the vehicle speed detector generates a first signal, and this first signal is sent to the switch. to open the switch, and when the vehicle speed reaches a second predetermined speed lower than the first predetermined speed, a second signal is generated from the vehicle speed detector, and this second signal is transmitted to the second predetermined speed. 1. A temperature control method for an oxygen sensor, characterized in that the temperature is sent to a switch to close the switch.