JPH09152417A - Heater electric energization control method for oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain an oxygen concentration detector at a specified temperature through the control of electric energization of a heater by determining the temperature of the heater accurately even when an electrical resistivity changes. SOLUTION: Pads 18 and 19 comprising a conductive first metal material are arranged on the surface of a heater 16 and leads 25 and 26 comprising second metal material different in type from the first metal material are kept being pressed in contact with the pads 18 and 19. A voltage detector 29 is connected to the leads 25 and 26 and furthermore, a power source 27 is connected to the leads 25 and 26 through an opening/closed means 28. The power of the power source 27 is supplied to the heater 16 by a closed path of the opening/closing means 28 while an electromotive force generated at contact parts 44 and 45 between the pads 18 and 19 and the leads 25 and 26 is measured by the voltage detector 29 as factor corresponding to the temperature of the heater 16 in the closed path of the opening/closing means 28. The results of the measurement are reflected on the control of the electric energization of the heater 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor provided with an oxygen concentration detecting element and a heater, which controls the energization of the heater to heat the heater to keep the oxygen concentration detecting element at a predetermined temperature. And a heater energization control method for the oxygen sensor.

[0002]

2. Description of the Related Art In recent vehicles, the oxygen concentration in exhaust gas discharged from an internal combustion engine is detected by an oxygen concentration detecting element of an oxygen sensor, and the detected value is used to determine the air-fuel ratio (the weight ratio of air and fuel). ) Is widely practiced. Normally, in this oxygen sensor, the characteristics of the oxygen concentration detecting element depend on temperature, so a heater is provided to stabilize the operation, and this heater is used to maintain the oxygen concentration detecting element at a predetermined temperature.

An example of such an oxygen sensor is disclosed in JP-A-60-239664. In this technique, paying attention to the close correlation between the heater temperature and the resistance value, the resistance value of the heater is obtained from the current supplied to the heater and the applied voltage. The heater temperature is calculated according to the resistance value according to a predetermined arithmetic expression, and the energization of the heater is controlled based on the calculated value.

[0004]

However, for example, in a heater formed by printing a paste containing a metal powder as a main component, metal particles are not integrated, and a coarse contact is generated at a contact portion between particles. May have a portion that has become. In this case, when the heater is energized due to the use of the oxygen sensor, heat is locally generated at a portion having a high electric resistance (a portion having a coarse density). When the heat generation temperature rises to near the melting point of the metal particles, the sintering of the metal particles progresses and agglomerates, and the resistivity of the heater changes. Therefore, if the conventional technique is applied to the oxygen sensor having such a heater, there is a possibility that a difference may occur between the calculated heater temperature and the actual heater temperature. As a result, it becomes difficult to maintain the oxygen concentration detection element at a predetermined temperature by controlling the energization of the heater.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to accurately detect the heater temperature even when the resistivity of the heater fluctuates, and detect the oxygen concentration by controlling the energization of the heater. To ensure that the element is maintained at a given temperature.

[0006]

In order to achieve the above object, the present invention provides a method for maintaining the oxygen concentration detecting element at a predetermined temperature by controlling the energization of the heater to cause the heater to generate heat. A first metal material having conductivity is disposed on the surface of the heater, and a second metal material of a different type from the same metal material is brought into contact with the first metal material in a pressed state. A voltage detector is connected to the second metal material, a heater power supply source is connected to the second metal material via an opening / closing means, and the heater power supply source is connected to the heater by closing the opening / closing means. And the electromotive force generated at the contact portion of the two metal materials when the opening / closing means is opened, is measured by the voltage detector as an element corresponding to the temperature of the heater, and the measurement result is controlled to control the energization of the heater. Reflected in It is way.

According to the above invention, the electric power from the heater power supply source is supplied to the heater when the opening / closing means is closed. The heater generates heat, and the heat generation heats the oxygen concentration detection element. On the other hand, when the opening / closing means is open, the electromotive force generated at the contact portion between the first metal material and the second metal material is measured by the voltage detector. This electromotive force has nothing to do with the resistivity of the heater and corresponds only to the actual temperature of the heater. Then, this electromotive force is reflected in the energization control. At this time, if the energization of the heater is controlled so that the electromotive force corresponding to the actual heater temperature becomes the voltage value corresponding to the target heater temperature as described above, the temperature of the heater converges to the target value. The oxygen concentration detecting element is maintained at a predetermined temperature.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below. FIG. 2 shows a schematic configuration of the oxygen sensor 11 to which the control method of the present embodiment is applied. The oxygen sensor 11 includes a case 12 arranged in an exhaust passage of an internal combustion engine, an element holding unit 13 mounted in the case 12, a terminal holder 14 arranged in the case 12 above the element holding unit 13, and the like. It is configured. The element holding unit 13 includes an oxygen concentration detection element 15 for detecting the oxygen concentration in the exhaust gas flowing through the exhaust passage, and a heater 16 for maintaining the detection element 15 at a predetermined temperature. The oxygen concentration detection element 15 and the heater 16 are both elongated,
Are joined together. A pair of pads 17 (only one is shown) are formed on the upper side surface of the oxygen concentration detection element 15 by printing, plating, etc., and a pair of pads 18, 19 are formed on the upper side surface of the heater 16 by printing, plating, etc. There is. Here, in order to distinguish the two pads 18 and 19 on the side surface of the heater 16, one is referred to as a first pad 18 and the other is referred to as a second pad 19.

The upper portion of the terminal holder 14 accommodates the same number of connection fittings 20 and 21 as the pads 17 to 19, and the lead wires 22, 21 are provided on the upper ends of the connection fittings 20 and 21, respectively.
23 are connected by fastening means such as caulking. Each of the lead wires 22 and 23 passes through the terminal holder 14 and extends to the outside of the case 12. Also, each connection fitting 2
Leads 24, 25, 26 are attached to the lower ends of 0, 21. The lower half of each of the leads 24 to 26 is bent in a substantially J shape toward the oxygen concentration detecting element 15 or the heater 16 and is in contact with the corresponding pad 17 to 19 in a pressed state. Here, in order to distinguish the two leads 25, 26 on the side of the heater 16 in particular, one of them is used as the first lead 25.
And the other is the second lead 26.

As shown in FIG. 3, the pads 18 and 1 are
9 is formed of a conductive first metal material,
Each lead 25, 26 has a second
It is made of a metallic material. Both metal materials have the function of a thermocouple, and contact portions 44, 4 of each other.
5, the voltages V1 and V corresponding to the temperature of the heater 16
Raises 2. As such a dissimilar metal material, platinum (Pt) simple substance and a mixture of platinum and rhodium (Rh) are suitable. One of these combinations is the first
And the other is used as the second metal material. Particularly, in the present embodiment, the metal material forming the second pad 19 is different from the metal material forming the first pad 18, and the metal material forming the second lead 26 is different from the metal material forming the first lead 25. Is different.
For example, the first pad 18 is made of platinum, and the first lead 2
If 5 consists of a mixture of platinum and rhodium, a second
The pad 19 is made of the same mixture, and the second lead 26 is made of platinum.

FIG. 1 shows an electric circuit for controlling the energization of the heater 16 to cause the heater 16 to generate heat and maintain the oxygen concentration detecting element 15 at a predetermined temperature. This circuit includes the heater 16, the first pad 18,
In addition to the second pad 19, the first lead 25, and the grounded second lead 26, a power supply 27 as a heater power supply source,
Switching means 28, voltage detector 29, and electronic control unit (Elect
ronic Control Unit, hereinafter simply referred to as "ECU") 30
It has.

The switching means 28 comprises a transistor 31 and three resistors 32, 33 and 34. The collector of the transistor 31 is connected to the first lead 25, and the emitter of the transistor 31 is connected to the power supply 27 through the transistor protection resistor 32. The base is connected to an output terminal 36 of the ECU 30 via a resistance 33 for noise suppression. Resistance 34
Is for ensuring that the transistor 31 performs a switching operation, and includes a power source 27, a base and a resistor 33.
It is provided between the connection point a and the connection point a.

The voltage detector 29 comprises a differential amplifier circuit 38 using an operational amplifier 37 and an A / D converter 39, and has a high impedance. The first lead 25 is connected to the inverting input terminal of the operational amplifier 37 via the resistor 40. A resistor 41 is provided between the output terminal of the operational amplifier 37 and the inverting input terminal so that part of the output voltage is returned to the inverting input terminal (negative feedback is applied). The non-inverting input terminal of the operational amplifier 37 is grounded through the resistor 42 and the resistor 43. The resistances of the resistors 41 and 43 are the same (R1)
And the resistance values of the resistors 40 and 42 are the same (R2
). This differential amplifier circuit 38 includes an operational amplifier 37.
The difference between the voltages V1 and V2 (V
1-V2) is amplified (R1 / R2) times and output.

The A / D converter 39 is provided between the output terminal of the operational amplifier 37 and the input terminal 35 of the ECU 30, and converts the output voltage of the operational amplifier 37 into a digital value. The ECU 30 is composed of an input signal processing circuit, an arithmetic circuit, a drive circuit, a power supply circuit, etc., reads the A / D conversion value V from the input terminal 35, and performs a predetermined arithmetic operation based on the value V. Then, according to the calculation result, the transistor 31 is switched to control the energization of the heater 16.

Next, the operation and effect of this embodiment configured as described above will be described. The flowchart of FIG. 4 shows the process executed by the ECU 30.
The routine for controlling the energization to the heater 16 is shown and is executed at a predetermined timing.

When this routine is entered, the ECU 30 first determines in step 101 whether the operating condition of the engine is the high load condition. This determination is made, for example, by comparing the opening of the throttle valve (throttle opening) provided in the intake passage of the engine with a predetermined value. If the throttle opening is equal to or smaller than the predetermined value, the engine is in a low / medium load state, that is, the determination condition of step 101 is not satisfied, and the oxygen concentration detecting element 15 of the oxygen sensor 11 is not satisfied.
It is determined that the temperature is less than or equal to the predetermined value, and the transistor 31 is turned on in step 105. Then power supply 2
The electric power of 7 is supplied to the heater 16 (the heater 16 is energized), the heater 16 generates heat, and the temperature of the detection element 15 rises. After executing the processing of step 105, this routine is ended.

On the other hand, if the throttle opening is larger than the predetermined value, the engine is in a high load state, that is, the judgment condition of step 101 is satisfied, the exhaust gas becomes high temperature, and the temperature of the oxygen concentration detecting element 15 becomes high. It is determined that the transistor 31 is sufficiently high, and the transistor 31 is turned off in step 102. Then, the power of the power source 27 is not supplied to the heater 16 (the heater 16 is not energized), and the heater 16 stops generating heat.

Next, at step 103, the A / D converted value V by the A / D converter 39 is read. This A / D conversion value V reflects the temperature of the heater 16 itself.
In step 104, it is determined whether the A / D conversion value V is greater than or equal to a predetermined determination value α. When this determination condition is satisfied (V ≧ α), this routine is once ended. That is, the transistor 31 is kept off, and the energization of the heater 16 is stopped.

On the other hand, if the determination condition of step 104 is not satisfied (V <α), the process proceeds to step 105, and the transistor 31 is turned on in the same manner as described above.
Then, the heater 16 is energized to generate heat and the temperature of the oxygen concentration detection element 15 rises. After executing the processing of step 105, this routine is ended.

As described above, in the present embodiment, when the engine is in the low / medium load state, the transistor 31 is turned on (the opening / closing means 28 is closed), and the electric power of the power supply 27 is supplied to the heater 16. The heater 16 generates heat and the oxygen concentration detection element 15 is heated. On the other hand, when the engine is under high load, the transistor 31 is turned off (the opening / closing means 28 is opened). At this time, the contact portions 44, 45 of the pads 18, 19 and the leads 25, 26
Electromotive force (voltages V1 and V2) generated in the differential amplifier circuit 3
It is detected and amplified by 8, and converted into a digital value by the A / D converter 39. This electromotive force has nothing to do with the resistivity of the heater 16 and corresponds only to the actual temperature of the heater 16. Then, this electromotive force is reflected in the energization control. That is, since the energization of the heater 16 is controlled so that the electromotive force corresponding to the actual heater temperature becomes the voltage value (determination value α) corresponding to the target heater temperature as described above, the temperature of the heater 16 is controlled. Can be converged to a target value and the oxygen concentration detection element 15 can be maintained at a predetermined temperature.

The present embodiment has the following features in addition to the matters described above. (A) In the conventional technique, two measurements of voltage and current are required for one measurement object called heater temperature, whereas in the present embodiment, only the heater temperature needs to be measured.

(B) In order to detect the temperature of the heater 16, it is conceivable to add a dedicated temperature sensor in addition to this embodiment and the prior art. However, this causes a problem that the number of parts increases and the cost increases. On the other hand, in the present embodiment, attention is paid to the fact that the pads 18 and 19 and the leads 25 and 26 are used in the electrically connecting portion between the heater 16 and the lead wire 23, and the types of these materials are devised. , Contact parts 44, 45
The electromotive force corresponding to the heater temperature is generated. That is, some of the components of the electric circuit for controlling the energization of the heater 16 are diverted as some of the components for detecting the heater temperature. Therefore, it is possible to reduce the number of parts to be added for detecting the heater temperature, and to suppress the cost increase.

(C) When the energization of the heater 16 is stopped, the oxygen concentration detecting element 15 is warmed only by the heat of the exhaust gas. At this time, if the heater 16 is not energized even if the load of the engine is reduced and the temperature of the exhaust gas is reduced, the temperature of the oxygen concentration detection element 15 may be reduced and the element 15 may not function. In contrast,
In the present embodiment, the electromotive force at the contact portions 44 and 45 is detected when the power supply to the heater 16 is stopped. Then, based on the comparison between the electromotive force and the determination value α, the heater 16 is energized or the energization is stopped. Therefore, as described above, it is possible to energize the heater 16 and perform the same function before the temperature of the element 15 decreases and the element 15 stops functioning.

(D) If the impedance of the differential amplifier circuit 38 is low, when the transistor 31 is turned on in step 105 of FIG. 4, a part of the power of the power supply 27 will be consumed by the circuit 38. On the other hand, in the present embodiment, since the differential amplifier circuit 38 has high impedance, almost no current flows there, and the power of the power supply 27 is hardly consumed by the circuit 38. Therefore, the heater 16 can efficiently generate heat.

(E) Utilizing the voltages V1 and V2 at the two contact portions 44 and 45, the difference between them is used as the differential amplifier circuit 38.
It is amplified by. Therefore, a higher voltage can be detected than in the case where the voltage at one contact portion is used, and the detection accuracy can be improved.

The present invention can be embodied in another embodiment described below. (1) The duty ratio of the energization time to the heater 16 may be controlled. In this case, the contact portion 4 when the power is stopped
The voltages V1 and V2 at 4 and 45 are detected as elements corresponding to the heater temperature, and the detection result is reflected in the energization control.
By doing so, during heating of the oxygen concentration detecting element 15,
The heater temperature can be measured with high accuracy. It is possible to prevent the heater temperature from rising excessively.

(2) As the first and second metal materials,
Other than the above-mentioned ones (platinum alone and a mixture of platinum and rhodium), ones which generate a stable voltage corresponding to the temperature of the heater 16 may be used.

(3) Pads 18, 19 and leads 25,
26 may be platinum, or a mixture of platinum and rhodium, in at least those contact portions 44, 45. Therefore, for example, most of the pads 18 and 19 and the leads 25 and 26 are made of another conductive metal material, and a film made of platinum or a film made of a mixture of platinum and rhodium is formed on the contact portion by printing or plating. You may.

(4) Pad 1 in the above embodiment
Only one of the contact portions 44, 45 of 8, 19 and leads 25, 26 may be made of platinum or a mixture of platinum and rhodium.

(5) The voltages at the contact portions 44 and 45 may be detected, and the average value of the two may be reflected in the energization control of the heater 16 as an element corresponding to the temperature of the heater 16.

Although the respective embodiments of the present invention have been described above, technical ideas other than the claims which can be understood from the respective embodiments will be described below together with their effects. (A) In the control method according to claim 1, one of the first and second metal materials is platinum, and the other is a mixture of platinum and rhodium. By doing so, an electromotive force corresponding to the heater temperature can be reliably generated at the contact portion between the two metal materials.

(B) In the control method according to the first aspect of the present invention, the energization control of the heater is performed by energizing the heater to generate heat when the internal combustion engine is under low / medium load, and at the same time when the internal combustion engine is high. The oxygen concentration detection element is maintained at a predetermined temperature by stopping the energization of the heater when a load is applied, and the heater is energized when the measurement result by the voltage detecting means falls below a predetermined value when the energization is stopped. Method for controlling heater energization of oxygen sensor. By doing so, the temperature of the heater is converged to a predetermined value and the element temperature of the oxygen concentration detection element is made higher than in the case where the heater is energized or stopped only by the operating state of the internal combustion engine. It is possible to maintain high accuracy.

[0033]

As described in detail above, according to the present invention, the electromotive force generated at the contact portion between the first metal material and the second metal material is measured as an element corresponding to the heater temperature, and the heater Since it is reflected in the energization control, it is possible to accurately grasp the heater temperature even if the heater resistivity fluctuates, and to reliably maintain the oxygen concentration detection element at a predetermined temperature by the energization control of the heater. It will be possible.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram for controlling energization of a heater.

FIG. 2 is a sectional view of an oxygen sensor.

3 is an enlarged view of a contact portion between a pad and a lead in FIG.

FIG. 4 is a flowchart illustrating a heater energization control routine by the ECU.

[Explanation of symbols]

15 ... Oxygen concentration detecting element, 16 ... Heater, 18 ... First pad, 19 ... Second pad, 25 ... First lead, 26 ... Second lead, 27 ... Power source as heater power supply source, 28
... Opening / closing means, 29 ... Voltage detectors, 44, 45 ... Contact portions.

Claims (1)

[Claims] 1. A method for controlling the energization of a heater to cause the heater to generate heat to maintain the oxygen concentration detection element at a predetermined temperature, wherein the first metal material having conductivity is used as the heater. The second metal material different from the same metal material in contact with the first metal material in a pressed state, and a voltage detector is connected to the second metal material. A heater power supply source is connected to the metal material of No. 2 through an opening / closing means, the power of the heater power supply source is supplied to the heater by a closing path of the opening / closing means, and both metal materials are opened when the opening / closing means is opened. A method for controlling heater energization of an oxygen sensor, wherein an electromotive force generated at a contact portion of the oxygen sensor is measured by the voltage detector as an element corresponding to the temperature of the heater, and the measurement result is reflected in the energization control of the heater.