JP2511087B2 - Heater temperature controller for oxygen concentration sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heater temperature control device for an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas of an internal combustion engine.

BACKGROUND ART In order to purify exhaust gas of an internal combustion engine, improve fuel efficiency, etc., the oxygen concentration in exhaust gas is detected by an oxygen concentration sensor,
An air-fuel ratio control device for feedback-controlling the air-fuel ratio of an air-fuel mixture supplied to an engine by adjusting the amount of air or the amount of fuel in accordance with the value detected by an oxygen concentration sensor is disclosed in, for example, Japanese Patent Laid-Open No. 62- It is known from the publication 225943.

In an oxygen concentration sensor used in such an air-fuel ratio control device, an oxygen concentration detecting element made of an oxygen ion conductive solid electrolyte material is usually provided. Especially when the oxygen concentration detecting element is an element proportional to oxygen concentration, unless the temperature is sufficiently higher than the exhaust gas temperature during the steady operation of the engine, the oxygen concentration detecting element is not activated and desired oxygen concentration detecting characteristics cannot be obtained. Therefore, an electric heater for heating the oxygen concentration detecting element is provided, and when the engine operation is started, a current is applied to the heater from the heater temperature control device to heat the heater.

In such a heater temperature control device, in order to maintain the temperature of the oxygen concentration detecting element at an appropriate temperature, a voltage is applied to the heater so that the heater resistance value becomes a predetermined value. This is because the temperature of the oxygen concentration detecting element is proportional to the heater resistance value as shown by the solid line a in FIG. However, the relationship between the heater resistance value and the temperature of the oxygen concentration detecting element varies depending on the exhaust gas temperature and the exhaust flow rate as shown by the broken lines b and c in FIG.

FIG. 2 shows temperature states of the heater position and the oxygen concentration detection element position when the exhaust gas temperature is high (Texh _H ) and low (Texh _L ). From this figure, the heating value of the heater,
That is, even if the target temperature is the same, when the exhaust gas temperature is high, the temperature at the heater position is much higher than the target temperature, and conversely, when the exhaust gas temperature is low, the temperature at the heater position is near the target temperature. However, it can be seen that the temperature at the oxygen concentration detecting element position becomes lower than the target temperature. It is considered that this is because the amount of heat transfer differs depending on the difference between the exhaust gas temperature and the temperature at the heater position. That is, when the exhaust gas temperature is high, the exhaust gas acts to heat the heater, but when the exhaust gas temperature is low, the exhaust gas acts to cool the heater. Further, since there is a predetermined distance between the heater position and the oxygen concentration detection element position, even if the heater temperature is controlled to the target temperature, the temperature at the oxygen concentration detection element position falls below the target temperature, and particularly high exhaust gas The lower the gas temperature, the greater the degree of decrease. Therefore, even if the heater resistance value is controlled to a predetermined value in order to maintain the oxygen concentration detecting element temperature at the target temperature, if the exhaust gas temperature changes as shown in FIG. 3, the temperature of the oxygen concentration detecting element changes. However, if the temperature of the oxygen concentration detecting element is too high or too low, not only the oxygen concentration detecting accuracy deteriorates but also the durability of the element itself deteriorates. It was also found that when the exhaust gas flow rate changes, the heater temperature also changes, and as a result, the temperature of the oxygen concentration detecting element changes.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a heater temperature control device for an oxygen concentration sensor that can maintain the temperature of the oxygen concentration detection element at an appropriate temperature.

In a heater temperature control device for an oxygen concentration sensor according to the first aspect of the present invention, a power detection unit that detects power consumption of an electric heater, a setting unit that sets a target heater resistance value according to the detected power consumption, and a heater. And a voltage applying means for applying a voltage to the heater so that the resistance value of the heater becomes equal to the target heater resistance value. Further, in the heater temperature control device for the oxygen concentration sensor according to the second aspect of the present invention, the power detection means for detecting the power consumption of the electric heater, the flow rate detection means for detecting the exhaust gas flow rate of the engine, and the detected power consumption and It is characterized by comprising setting means for setting a target heater resistance value according to the exhaust gas flow rate and voltage applying means for applying a voltage to the heater so that the resistance value of the heater becomes equal to the target heater resistance value.

Examples Hereinafter, examples of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 4 shows an oxygen concentration detecting element of an oxygen concentration sensor having a heater temperature control device according to the present invention. In this oxygen concentration detection element, a gas retention chamber 2 is formed in the oxygen ion conductive solid electrolyte material 1 as a gas diffusion limited area. The gas retention chamber 2 communicates with an introduction hole 3 for introducing the exhaust gas of the gas to be measured from outside the solid electrolyte material 1. The introduction hole 3 allows the exhaust gas to flow into the gas retention chamber 2 in the exhaust pipe of an internal combustion engine (not shown). Positioned for ease. Further, the oxygen ion conductive solid electrolyte material 1 is formed with an atmosphere reference chamber 4 for introducing the atmosphere so as to separate the wall from the gas retention chamber 2. An electrode protection hole 5 is formed in the wall of the gas retention chamber 2 on the side opposite to the atmospheric reference chamber 4. Gas retention chamber 2
The electrode pair 6a, 6b is formed on the wall between the electrode protection hole 5 and the electrode protection hole 5, and the electrode pair 7a, 7b is formed on the wall between the gas retention chamber 2 and the atmospheric reference chamber 4. . The solid electrolyte material 1 and the electrode pairs 6a, 6b act as the oxygen pump element 8, and the solid electrolyte material 1 and the electrode pairs 7a, 7b act as the battery element 9.
Further, electric heaters 10a and 10b are provided on the outer wall surfaces of the air reference chamber 4 and the electrode protection hole 5, respectively. The heaters 10a and 10b are connected in parallel with each other.

ZrO ₂ (zirconium dioxide) is used as the oxygen ion conductive solid electrolyte material 1, and Pt (platinum) is used as the electrodes 6a to 7b.

A voltage corresponding to the oxygen concentration difference between the gas retention chamber 2 and the atmospheric reference chamber 4 is generated between the electrodes 7a and 7b of the battery element 9, and the voltage is supplied to pump current control means (not shown). The pump current control means supplies a pump current between the electrodes 6a and 6b of the oxygen pump element 8 so that the generated voltage of the battery element 9 becomes equal to the reference voltage corresponding to the theoretical air-fuel ratio.

As shown in FIG. 5, a current detection resistor 11 is connected in series with the heaters 10a and 10b. The voltage across the heaters 10a and 10b and the voltage across the current detection resistor 11 are supplied to the A / D converter 12. An absolute pressure sensor 13 is connected to the A / D converter 12. The absolute pressure sensor 13 is an engine intake pipe (not shown)
It is provided inside and generates the voltage of the level according to the absolute pressure in the intake pipe. Each voltage signal digitized by the A / D converter 12 is supplied to the microprocessor 15. A drive circuit 16 is connected to the microprocessor 15, and the drive circuit 16 supplies a voltage according to a command from the microprocessor 15 to the heater 10a,
It is applied to a series circuit composed of 10b and a resistor 11. ROM 21 and RAM 22 are connected to the microprocessor 15 as storage elements.

On the other hand, the crank angle sensor 17 uses a pulse synchronized with the rotation of the crankshaft (not shown) of the engine, for example, TD.
Generate a C pulse. The output pulse of the crank angle sensor 17 is supplied to the counter 19 via the waveform shaping circuit 18. The counter 19 measures the generation interval of the output pulse of the waveform shaping circuit 18 by the number of clock pulses output from a clock pulse generation circuit (not shown) and supplies it to the microprocessor 15 as engine speed Ne data.

In such a configuration, the absolute pressure P _{BA in the} intake pipe from the A / D converter 12, the voltage V _H across the heaters 10a and 10b, and the current detection resistance.
Each information of heater current I _H detected as voltage across 11
Information representing the engine speed Ne is also supplied from the counter 19 to the microprocessor 15.

The microprocessor 15 sets the applied voltage of the drive circuit 16 on a predetermined cycle basis based on each information as shown below.

As shown in FIG. 6, the microprocessor 15 first reads the intake pipe absolute pressure P _BA , the both-end voltage V _H of the heaters 10a and 10b, the heater current I _H , and the engine speed Ne (step 51). , The voltage V across the read heaters 10a and 10b
_H and heater current I _H to heater power consumption W _H (= V _H × I _H )
Is calculated (step 52), and the exhaust gas flow rate Q is calculated from the read absolute pressure P _BA and engine speed Ne (step 53). The exhaust gas flow rate Q is calculated, for example, by the equation Q = K × Ne × P _BA . In this equation, K is a constant. After calculating the heater power W _H and the exhaust gas flow rate Q, the heater according to the heater power W _H and the exhaust gas flow rate Q
The target resistance value R _TAR of 10a and 10b is set (step 54).
Exhaust gas flow rate Q, heater power consumption _WH and target resistance value R _TAR
The target resistance value R _TAR is set lower as the exhaust gas flow rate Q increases, and the heater power consumption W _H is higher as the heater power consumption W _H rises within a predetermined temperature range. Is set. Since the setting data of the target resistance value R _TAR is written in the ROM 21 as a data map in advance, the microprocessor 15 searches the data map for the target resistance value R _TAR corresponding to the exhaust gas flow rate Q and the heater power consumption W _H. To set. As the heater power consumption W _H increases, the oxygen concentration detecting element temperature, that is, the heater resistance value needs to be increased. However, there is a distance between the heater position and the oxygen concentration detecting element position as shown in FIG. When the gas temperature is high or when the exhaust gas flow rate Q increases, the temperature at the heater position becomes higher than the target temperature, that is, the target resistance value R _TAR , so the target resistance value R _TAR is corrected to be low as shown in FIG. 7. The functional expression of the heater power consumption _WH and the target resistance value R _TAR may be stored for each exhaust gas flow rate Q, and the target resistance value R _TAR may be calculated by such a functional expression.

After setting the target resistance value R _TAR in this way, the heater resistance value R _H (= V _H / I _H ) of the heaters 10a and 10b is calculated from the read voltage V _H across the heaters 10a and 10b and the heater current I _H. Calculate (step 55). Next, the heater resistance value R _H and the target resistance value
The difference between the _{R TAR ΔR (= R H -R} TAR) were calculated (Step 5
6) The applied voltage command corresponding to the difference ΔR is generated for the drive circuit 16 (step 57). When ΔR ≧ 0, an applied voltage command is generated so as to decrease the applied voltage from the drive circuit 16 to the series circuit including the heaters 10a and 10b and the resistor 11, and when ΔR <0, increase the applied voltage. The drive circuit 16 responds to the applied voltage command by the heaters 10a and 10b and the resistor 1
Increase or decrease the voltage applied to the series circuit consisting of 1. When the voltage applied to the series circuit rises, the heat generation temperature of the heater rises, and as a result, the heater resistance value R _H increases. Further, when the voltage applied to the series circuit decreases, the heat generation temperature of the heater decreases, and as a result, the heater resistance value R _H decreases. That is, the applied voltage to the series circuit is controlled so that the heater resistance value R _H becomes equal to the target resistance value R _TAR .

FIG. 8 shows another embodiment of the present invention. In this heater temperature control device, the heaters 10a and 10b and the resistor 11
A series circuit including resistors 23 and 24 is connected in parallel to the series circuit including to form a bridge circuit. In this bridge circuit, the voltage V _B is the collector of NPN transistor 25.
Applied across the emitters. The voltage Va across the resistor 11 and the voltage Vb across the resistor 24 are supplied to the differential amplifier circuit 26. The output voltage of the differential amplifier circuit 26 is supplied to the base of the transistor 25. That is, a current corresponding to the difference voltage between the voltages Va and Vb is supplied from the transistor 25 to the heaters 10a and 10b. A variable resistor 27 is connected in parallel to the resistor 24, and the control end of the variable resistor 27 is connected to the microprocessor 15. The microprocessor 15 adjusts the resistance value of the variable resistor 27 according to the above-mentioned target resistance value R _TAR . When the resistance value of the variable resistor 27 changes, the voltage Vb changes, whereby the applied voltage of the bridge circuit is controlled so that the heater resistance value R _H becomes equal to the target resistance value R _TAR . Instead of the variable resistor 27, a series circuit of a resistor and an on / off switch may be connected in parallel with the resistor 24 to turn on / off the switch depending on the target resistance value R _TAR .

In each of the above examples, the target resistance value R _TAR is set according to the detected heater power consumption and exhaust gas flow rate,
Heater 10a as the heater resistance value R _H is equal to the target resistance R _TAR, although a voltage is applied to 10b, setting the target resistance R _TAR in accordance with only the heater power consumption is detected, the heater resistance value R _H heater 10a, 10 as but becomes equal to the target resistance value R _TAR
Even if a voltage is supplied to b, the temperature of the oxygen concentration detecting element can be properly controlled to an appropriate temperature.

As described above, in the heater temperature control device for the oxygen concentration sensor of the present invention, the target resistance value is set according to the power consumption of the heater, and the heater voltage is set so that the heater resistance value becomes equal to the target resistance value. Is applied, it is possible to favorably control the oxygen concentration detection element to the target temperature even when the heat generation state of the heater changes due to the change in exhaust gas temperature. Also,
If the target resistance value is set according to the heater power consumption and the exhaust gas flow rate, and a voltage is applied to the heater so that the heater resistance value becomes equal to the target resistance value, the oxygen concentration detection element can be better controlled by the target temperature. You can Therefore, it is possible to prevent deterioration of oxygen concentration detection accuracy and deterioration of the element.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a heater resistance value and an oxygen concentration detecting element temperature, FIG. 2 is a diagram showing a temperature state between a heater position and an oxygen concentration detecting element position, and FIG. 3 is an exhaust gas temperature and an oxygen concentration. FIG. 4 is a diagram showing the relationship with the detection element temperature, FIG. 4 is a diagram showing an oxygen concentration detection element of an oxygen concentration sensor equipped with the heater temperature control device according to the present invention, and FIG. 5 is an embodiment of the heater temperature control device according to the present invention. 6 is a flow chart showing the operation of the microprocessor in the device of FIG. 5, FIG. 7 is a diagram showing target resistance value setting characteristics, and FIG. 8 is another embodiment of the present invention. It is a circuit diagram shown. Explanation of symbols of main parts 1 …… Oxygen ion conductive solid electrolyte material 2 …… Gas retention chamber 4 …… Atmosphere reference chamber 8 …… Oxygen pump element 9 …… Battery element 10a, 10b …… Heater 11 …… Current detection Resistance 13 …… Absolute pressure sensor 17 …… Crank angle sensor 19 …… Counter

Claims (2)

(57) [Claims] 1. A heater temperature control of an oxygen concentration sensor having an oxygen concentration detecting element, which is provided in an exhaust system of an internal combustion engine, for generating an output according to the oxygen concentration in exhaust gas, and an electric heater for heating the oxygen concentration detecting element. In the device, power detection means for detecting power consumption of the heater, setting means for setting a target heater resistance value according to the detected power consumption, and the resistance value of the heater equal to the target heater resistance value. A heater temperature control device comprising: a voltage applying unit that applies a voltage to the heater. 2. A heater temperature control of an oxygen concentration sensor having an oxygen concentration detecting element, which is provided in an exhaust system of an internal combustion engine, for generating an output according to the oxygen concentration in exhaust gas, and an electric heater for heating the oxygen concentration detecting element. A device for setting power detection means for detecting power consumption of the heater, flow rate detection means for detecting exhaust gas flow rate of the engine, and setting a target heater resistance value according to the detected power consumption and exhaust gas flow rate. A heater temperature control device comprising: setting means and voltage applying means for applying a voltage to the heater so that the resistance value of the heater becomes equal to a target heater resistance value.