JP3296282B2 - Element temperature detection device for gas concentration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting an element temperature of a gas concentration sensor, and more particularly to a gas concentration sensor for detecting the concentration of a specific component in exhaust gas from a vehicle-mounted engine. The present invention relates to a device for detecting the element temperature of the sensor.

[0002]

2. Description of the Related Art In recent years, in air-fuel ratio control of an on-vehicle engine, there has been a demand for improving control accuracy and a demand for lean burn, for example.
2. Description of the Related Art A gas concentration sensor that detects the concentration of a specific component (for example, oxygen concentration) in exhaust gas from an engine in a wide area and linearly has been embodied. As one example, a limiting current type air-fuel ratio sensor is known. In such a gas concentration sensor, it is indispensable to maintain a sensor element made of a solid electrolyte or the like in an active state in order to maintain the detection accuracy of the gas concentration. In general, the sensor is controlled by energizing a heater attached to the sensor. The element is heated to maintain the active state.

[0003] In the control of the heater energization, a technique of detecting the temperature (element temperature) of a sensor element and performing feedback control so that the element temperature becomes a desired activation temperature (for example, about 700 ° C) has been disclosed. Have been. In this case, it has been proposed to detect the element impedance using the fact that the resistance (element impedance) of the sensor element has a predetermined correspondence with the element temperature, and to derive the element temperature from the detected element impedance. .

As one method for detecting the element impedance, for example, in the case of a limiting current type air-fuel ratio sensor, the voltage V
neg is applied, and the current value In flowing with the applied voltage is In
Measure the eg. Then, the device impedance is detected as the device impedance = Vneg / Ineg. In addition to this,
There is also a method of temporarily changing the applied voltage to the positive side or the negative side and detecting the element impedance (AC impedance) from the voltage change amount and the current change amount at that time.

[0005]

However, in the conventional technique, there is a problem that an error easily occurs at the time of conversion from the element impedance to the element temperature, and the accuracy of detecting the element temperature is reduced. That is, it is known that the element impedance and the element temperature have a relationship shown in FIG. In addition,
The vertical axis of FIG. 10 indicates an impedance count value obtained by converting the element impedance detected as described above by LSB conversion. In such a case, the impedance count value and the element temperature are not in a proportional relationship, and the impedance count value is significantly increased especially in a low temperature range of the element temperature.

For this reason, in the active temperature region, if the impedance count value differs by one count, the detected value of the element temperature will greatly deviate. For example, in a predetermined activation temperature range of the sensor element: When the impedance count value changes from “26” to “25”, the detection value of the element temperature changes from “746 ° C.” to “750”
° C] ・ When the impedance count value changes from “25” to “24”, the detected value of the element temperature changes from “750 ° C” to “760”.
° C ”, the amount of deviation in element temperature is large (and
There is a problem that the element temperature cannot be accurately detected.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an element temperature detecting device for a gas concentration sensor capable of improving the element temperature detecting accuracy. It is.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, the voltage applied to the sensor element of the gas concentration sensor is temporarily switched to a positive side or a negative side (voltage switching). Means), an element resistance is calculated as an admittance value from the voltage change amount and the current change amount accompanying the voltage switching (admittance value calculation means). Then, the element temperature is detected based on the calculated admittance value (element temperature detecting means).

According to the above configuration, upon detecting the element resistance, the admittance value which is the reciprocal of the element impedance is calculated. That is, when the voltage change amount is ΔV and the current change amount is ΔI, the admittance value Y is calculated as Y = ΔI / ΔV. By the way, in the present specification, when describing the “element resistance value”, “impedance value” and “admittance value” are subordinate concepts.
It is assumed that it includes.

As a result, the relationship between the conventional device in which the impedance value and the element temperature are not in a proportional relationship (the relationship in FIG. 10).
Unlike this, the element resistance can be grasped from the admittance value having a proportional relationship with the element temperature. Then, by detecting the element temperature from the admittance value, the detection accuracy is improved. More specifically, as shown in FIG. 9, even when the admittance count value is shifted by one count, the deviation amount of the element temperature is small (and the deviation amount is almost constant).
The detection error of the element temperature can be greatly reduced as compared with the conventional apparatus.

In particular, in the invention according to claim 2, the element temperature is detected based on the calculated admittance value in the activation temperature range of the gas concentration sensor. For example, when the air-fuel ratio sensor is embodied as a gas concentration sensor, element temperature control (such as heater control at a constant element temperature) can be performed satisfactorily under the active state of the sensor, and as a result, air-fuel ratio detection and air The fuel ratio feedback control can be performed.

In addition, in practice, as described in claim 3, the device temperature is detected by utilizing the fact that the calculated admittance value and the device temperature are in a proportional relationship. As described above, an element temperature is detected based on the calculated admittance value using an approximate straight line having a different slope for each of a plurality of areas divided within the activation temperature area of the gas concentration sensor. Detecting the element temperature by interpolating the map data in a temperature range equal to or lower than the activation temperature range of the gas concentration sensor; It is good to detect the element temperature by interpolation.

In short, as shown in FIG. 6, in the active temperature range (temperature range of about 625 ° C. or higher) of the gas concentration sensor, the element temperature and the admittance value are in a proportional relationship, and the relationship between them is a linear equation. (Straight line). At this time, it is possible to approximate with a single straight line, but as shown in the figure, by approximating with a plurality of straight lines having different slopes, the accuracy of element temperature detection is further improved (claim 4). By converting the admittance value to the element temperature using the linear equation in this way, the calculation load can be reduced as compared with the case where the element temperature is calculated from the conversion map.

However, in a temperature range lower than the activation temperature range of the gas concentration sensor, the proportional relationship between the element temperature and the admittance value is canceled. In addition, the temperature range (region below the active temperature range)
In, the relationship between the two on the coordinates of the element temperature and the admittance value becomes a non-linear relationship. Therefore, the element temperature is detected by data interpolation while using the conversion map.
6). In this case, the use of the conversion map may increase the calculation load, but the use of the map is limited to a temporary period until the sensor is activated. Such a defect is not continued.

According to a seventh aspect of the present invention, the voltage switching means sets a reference value in accordance with an operational amplifier, and detects a device temperature when a voltage value on a signal processing unit side of the shunt resistor exceeds the reference value. Is switched to the negative side, and if the voltage value on the signal processing unit side of the shunt resistor falls below the reference value, the applied voltage at the time of element temperature detection is switched to the positive side.

That is, in order to accurately obtain the voltage change amount and the current change amount, it is necessary to switch the applied voltage within the range of the output capability of the operational amplifier (for example, 1.5 to 4.5 V). In this case, for example, by switching the applied voltage in a direction having a margin with respect to the center voltage (reference value) of the output capability of the operational amplifier, the applied voltage can be prevented from sticking to the lower limit or the upper limit, and the element resistance (admittance) can be reduced. Value) can be prevented from deteriorating. Here, the signal processing unit that processes the sensor signal indicates an A / D converter (CPU) that inputs a voltage value detected by the shunt resistor.

Further, in the invention described in claim 8, the first CPU is configured to control the voltage switching means and the admittance value detection.
To have the means. The second CPU receives the computed admittance value by a first CPU, said element temperature detecting means for detecting the element temperature based on the admittance value thus received
Having .

Also in the invention of claim 8, when detecting the element resistance, the admittance value which is the reciprocal of the element impedance is used, so that the element resistance value can be grasped in accordance with the proportional relationship between the element temperature and the admittance value. As a result, similarly to the first aspect of the invention, the accuracy of detecting the element temperature can be improved. In addition, the first and second CPUs are appropriately assigned to the respective processes relating to the detection of the element temperature, whereby the efficiency of the calculation is improved. Incidentally, when applied to an existing air-fuel ratio control device, the first CPU corresponds to a CPU for detecting a sensor current (air-fuel ratio) and an element resistance, and a second CPU.
Corresponds to a CPU for executing heater control and air-fuel ratio control for maintaining sensor activation.

[0019] In practice, the first CPU, the Adomita
The arithmetic data is transmitted to the second CPU with a smaller number of bytes than when the admittance value is calculated by the sense value calculating means (Claim 9).
It is preferable that they are connected so as to be able to communicate with each other by MA communication (claim 10). According to such a configuration, the information of the element resistance can be transmitted with a small number of bytes while maintaining the accuracy of a necessary portion. Therefore, the effect that the load in the DMA communication can be greatly reduced can be obtained.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In the present embodiment,
The present invention is applied to an air-fuel ratio control system for a vehicle engine, and is embodied as an air-fuel ratio detection device of the system. An electronic control unit (hereinafter referred to as an in-vehicle ECU) mounted on a vehicle
) Performs air-fuel ratio feedback (F / B) control based on the detection result of a limiting current type air-fuel ratio sensor (A / F sensor) provided in the engine exhaust pipe,
While monitoring the element temperature of the A / F sensor, a heater heating control for constantly maintaining the A / F sensor in an active state is performed.
The details will be described below.

FIG. 1 is an electrical configuration diagram showing an outline of an on-vehicle ECU 1 and an A / F sensor 30 driven by the ECU 1. In FIG. 1, a vehicle-mounted ECU 1 includes a first CPU 11 and a second CPU 11 that can communicate with each other by DMA communication.
12 is provided. The A / F sensor 30 has a sensor element 32 and a heater 33 as its main components.

The first CPU 11 has an A / F sensor 30
A predetermined applied voltage is output to the (sensor element unit 32), and a current signal flowing with the applied voltage is taken in from the sensor 30. On the other hand, the second CPU 12
A / F sensor 3 from PU 11 via DMA communication line 13
Information on the element resistance of 0 is input, and the element temperature is detected based on the input information. Also, the second CPU 12
Determines the necessity of heating the A / F sensor 30 according to the detected element temperature, and determines the heater control circuit 1 according to the necessity.
Operate 4. When sensor heating is required, the heater control circuit 14 controls the heater 33 attached to the A / F sensor 30.
, And the sensor 30 is maintained at a predetermined activation temperature (about 700 ° C. in the present embodiment).

Here, the configuration of the A / F sensor 30 will be described with reference to FIG. 2, the A / F sensor 30 protrudes toward the inside of the engine exhaust pipe 39. The A / F sensor 30 is roughly composed of a cover 31, a sensor element 32, and a heater 33. The cover 31 has a U-shaped cross section, and a plurality of small holes 31a communicating with the inside and outside of the cover are formed in a peripheral wall thereof. The sensor element section 32 generates a limit current corresponding to the oxygen concentration in the air-fuel ratio lean region or the unburned gas (CO, HC, H2, etc.) concentration in the air-fuel ratio rich region.

The structure of the sensor element section 32 will be described in detail. In the sensor element portion 32, the exhaust gas side electrode layer 3 is formed on the outer surface of the solid electrolyte layer 34 formed in a cup shape in cross section.
6, and an atmosphere-side electrode layer 37 is fixed to the inner surface. A diffusion resistance layer 35 is formed outside the exhaust gas side electrode layer 36 by a plasma spraying method or the like. The solid electrolyte layer 34 is made of ZrO2, HfO2, ThO2, B
An oxygen ion conductive oxide sintered body in which CaO, MgO, Y2 O3, Yb2 O3 or the like is dissolved in i2 O3 or the like as a stabilizer is formed. The diffusion resistance layer 35 is made of alumina, magnesia, siliceous, spinel, It is made of a heat-resistant inorganic substance such as mullite. Both the exhaust gas side electrode layer 36 and the atmosphere side electrode layer 37 are made of a noble metal having a high catalytic activity such as platinum, and the surfaces thereof are subjected to porous chemical plating or the like. In addition, the area and thickness of the exhaust gas side electrode layer 36 are 10 to 100 mm∧.
2 (square millimeter) and about 0.5 to 2.0 μm, while the area and thickness of the atmosphere-side electrode layer 37 are 10 mm∧2 (square millimeter) or more and 0.5
It is about 2.0 μm.

The heater 33 is housed in the atmosphere-side electrode layer 37, and generates heat from the sensor element portion 32 by the heat generated by the heater 33.
(The atmosphere side electrode layer 37, the solid electrode layer 34, the exhaust gas side electrode layer 36, and the diffusion resistance layer 35) are heated. Heater 33
Has a sufficient heat generating capacity to activate the sensor element section 32.

In the A / F sensor 30 having the above-described structure, the sensor element section 32 generates a limit current corresponding to the oxygen concentration in a lean region from the stoichiometric air-fuel ratio point. In this case, the limit current corresponding to the oxygen concentration is determined by the area of the exhaust gas side electrode layer 36, the thickness of the diffusion resistance layer 35, the porosity, and the average pore diameter. The sensor element 32 is capable of detecting the oxygen concentration with a linear characteristic. However, a high temperature of about 600 ° C. or more is required to activate the sensor element 32. Since the activation temperature range of the part 32 is narrow,
By heating only the exhaust gas of the engine, the sensor element section 32 cannot be maintained in the active region. Therefore, in the present embodiment,
The heating control of the heater 33 heats the sensor element section 32 to the active temperature range. In a region richer than the stoichiometric air-fuel ratio, the concentration of carbon monoxide (CO) or the like in the unburned gas changes almost linearly with respect to the air-fuel ratio.
2 generates a limiting current corresponding to the concentration of CO or the like.

The voltage-current characteristics of the sensor element section 32 will be described with reference to FIG. According to FIG. 3, the current flowing into the solid electrolyte layer 34 of the sensor element portion 32 and the voltage applied to the solid electrolyte layer 34, which are proportional to the detected air-fuel ratio of the A / F sensor 30, have linear characteristics. I understand. In such a case, the straight line parallel to the voltage axis V specifies the limit current of the sensor element unit 32, and the increase or decrease of the limit current (sensor current) corresponds to the increase or decrease of the air-fuel ratio (that is, lean / rich). are doing. That is, the limit current increases as the air-fuel ratio becomes leaner, and decreases as the air-fuel ratio becomes richer.

In this voltage-current characteristic, a voltage region smaller than a linear portion parallel to the voltage axis V is a resistance dominating region. The inclination of the primary linear portion in the resistance dominating region is It is specified by the internal resistance (element resistance) of the solid electrolyte layer 34. Since the element resistance changes with a change in temperature, when the temperature of the sensor element section 32 decreases, the slope decreases due to an increase in element resistance.

On the other hand, in the in-vehicle ECU 1 shown in FIG.
The CPU 11 is provided with two terminals Ch1 and Ch2, which are input terminals of the A / D converter, and two terminals DAC1, DAC2, which are output terminals of the D / A converter.

The air-fuel ratio detecting circuit of the on-vehicle ECU 1 has the following main components: an inverting input terminal is connected to the A / F sensor 30 via a resistor R2;
The operational amplifier O connected to the plus side terminal AF + (ie, the terminal connected to the atmosphere side electrode layer 37 in FIG. 2).
A shunt resistor R connected between the plus terminal AF + of the A / F sensor 30 and the output terminal of the operational amplifier OP1;
3. The non-inverting input terminal is the positive terminal A of the A / F sensor 30
An operational amplifier OP2 connected to F + and having an inverting input terminal and an output terminal commonly connected; and a non-inverting input terminal connected to the output terminal of the operational amplifier OP1 and an inverting input terminal and an output terminal being commonly connected. And an operational amplifier OP3.

The shunt resistor R3 has a resistance of about 100Ω. The output terminals of the operational amplifiers OP2 and OP3 are connected to resistors R4 and R5, respectively. A low-pass filter (LPF) 20 including a resistor R1 and a capacitor C1 is connected to a non-inverting input terminal of the operational amplifier OP1.

Further, the air-fuel ratio detection circuit of the on-vehicle ECU 1 includes: an operational amplifier OP5 having a non-inverting input terminal connected to the terminal DAC1 of the first CPU 11 and an inverting input terminal and an output terminal commonly connected; The inverting input terminal is connected to the terminal DAC2 of the first CPU 11, and the output terminal is connected to the minus terminal AF- of the A / F sensor 30 via the resistor R6 (that is, to the exhaust gas side electrode layer 36 of FIG. 2). And an operational amplifier OP6 having an inverting input terminal connected to a minus terminal AF− of the A / F sensor 30 via a resistor R7.

The capacitor C3 is connected to the negative terminal AF- of the A / F sensor 30, and the diodes D1 and D2 are connected to the positive terminal AF + of the sensor 30. The capacitor C3 and two diodes D
Reference numerals 1 and D2 are provided for preventing a high-voltage surge or static electricity from entering a signal line connecting the air-fuel ratio detection circuit and the A / F sensor 30. In addition, the circuit
A capacitor or the like is appropriately provided mainly for the purpose of noise removal.

In the vehicle ECU 1 configured as described above, the voltage Vp output from the terminal DAC1 is output as the voltage Vo via the operational amplifier OP5 and the LPF20. Then, the same voltage Vo as the voltage output from the LPF 20 is supplied to the A / F sensor 30 by the circuit unit including the operational amplifier OP1, the resistor R2, and the shunt resistor R3.
To the plus terminal AF +. That is, the operational amplifier OP1 is connected to the output voltage Vo of the LPF 20 and the A / F sensor 3
Its own output voltage is changed so that the zero plus side terminal AF + coincides.

On the other hand, a terminal DAC2 of the first CPU 11 is connected to a minus side terminal AF- of the A / F sensor 30 by a circuit section including an operational amplifier OP6 and resistors R6 and R7.
, A negative reference voltage Vm (3.0 V in the present embodiment) is applied.

For this reason, the terminal DAC of the first CPU 11
1, the difference (Vp−Vm) between the voltages Vp and Vm output from the DAC 2 is the difference between the two terminals AF + and A + of the A / F sensor 30.
It is applied as a voltage for detecting the air-fuel ratio of the air-fuel mixture between AF-. For example, Vp = 3.3V, Vm = 3.0V
Then, 0.3 V is applied to the A / F sensor 30. Then, with the application of the voltage, the A / F sensor 30
A limiting current according to the oxygen concentration in the exhaust gas at that time flows.

Since the same current as the current (sensor current i) flowing through the A / F sensor 30 also flows through the shunt resistor R3, the potential difference between both ends of the shunt resistor R3 becomes a value proportional to the sensor current i. At this time, the same voltage Vo as the voltage applied to the plus side terminal AF + of the A / F sensor 30 is input to the terminal Ch1 via the operational amplifier OP2, and the shunt resistor R3 on the opposite side to the A / F sensor 30 is input. The same voltage Vi as the voltage is input to the terminal Ch2 via the operational amplifier OP3.

The first CPU 11 has terminals Ch1 and Ch2.
Are digitally converted by an internal A / D converter, and the voltage difference (Vi−Vo) is divided by the resistance value of the shunt resistor R3 to detect the sensor current i. Then, the first CPU 11 obtains an air-fuel ratio (oxygen concentration in exhaust gas) of the air-fuel mixture every 4 ms, for example, from the detected sensor current i.

On the other hand, the first CPU 11 changes the voltage applied to the A / F sensor 30 to detect the air-fuel ratio every predetermined time (for example, 128 ms) as shown in FIG. The element resistance of the F sensor 30 is detected. In the present embodiment, the voltage Vp of the terminal DAC1 is changed in a rectangular wave shape, and FIG.
Of the input voltage Vo. In addition,
The voltage Vp is converted into a voltage Vo having a predetermined time constant when passing through the LPF 20. FIG. 8 (b)
FIG. 8A is an enlarged view of a portion surrounded by an ellipse in FIG.

More specifically, the first CPU 11 detects the element resistance of the A / F sensor 30 in the following procedure. First, at time t1 in FIG. 8, the voltage Vo input to the terminal Ch1 is detected. The voltage detected at this time t1 is referred to as “Vo (t1)”.

At time t2 immediately after time t1, at terminal Ch2
Is detected. The voltage detected at this time t2 is referred to as “Vi (t2)”. At time t3 immediately after time t2, the output voltage Vp of the terminal DAC1 is changed to a voltage lower by ΔVa than the normal voltage for detecting the air-fuel ratio.

A predetermined time T1 from time t3
At the time t4 when has elapsed, the voltage Vi input to the terminal Ch2 is detected. The voltage detected at this time t4 is referred to as “Vi
(T4) ". The time T1 is set to a time at which the change ΔI of the sensor current I is expected to peak from time t3.

At time t5 immediately after time t4, the terminal Ch1
Is detected. The voltage detected at this time t5 is referred to as “Vo (t5)”. Then, the element resistance is calculated as the admittance value Y by the following equation (1). Note that the resistance value of the shunt resistance value R3 is Rs.

[0044]

(Equation 1) In the above equation (1), ΔVo (t1) −Vo
(T5)｝ is the change ΔV in the applied voltage, and the other part is the change ΔI in the sensor current. Equation (1)
{Vo (t1) −Vo (t5)} is a known Δ
It is also possible to replace with Va.

Thereafter, at time t6 when a predetermined time T2 has elapsed from time t3, the output voltage Vp of the terminal DAC1 is changed to a voltage higher by ΔVb than the normal voltage.

A predetermined time T3 from time t6
Has elapsed at time t7, the output voltage Vp of the terminal DAC1 is
To the normal voltage. At time t6 when the calculation of the element resistance (admittance value Y) is completed, the terminal DAC1
The reason why the output voltage Vp is changed to the positive side (opposite to the first change direction) from the voltage is to accelerate the convergence of the sensor current. That is, when the voltage applied to the A / F sensor 30 is returned to the normal voltage again, if the voltage is directly switched to the original normal voltage, the electric charge stored in the capacitance component of the element of the A / F sensor 30 is obtained. Due to the
The sensor current generates a peak current immediately after the return of the voltage, and as a result, the time until the sensor current converges to the original current value becomes longer. Therefore, in the present embodiment, when the applied voltage is returned to the original normal voltage, a voltage in a direction opposite to the previous voltage change is applied for a short time to discharge electric charge in the capacitance component of the element for a short time. And the time required for sensor current convergence is shortened. In this case, it is more effective if the voltage waveform is set so that the amount of electric charge moving in the element of the A / F sensor 30 becomes substantially the same regardless of the positive or negative change.

Next, the first CPU 11 in the on-vehicle ECU 1
Will be described with reference to the flowchart of FIG. The processing in FIG.
For example, it is executed at a cycle of 128 ms.

When the first CPU 11 starts the processing shown in FIG. 4, first, in step 101, the voltage Vi input to the terminal Ch2 is detected, and it is determined whether this voltage Vi is higher than a predetermined reference value. I do. The reference value is the operational amplifier OP
1 (see FIG. 1) corresponds to the center voltage of the output capability. In the present embodiment, the output capability of the operational amplifier OP1 is 1.5 to
It is assumed that the voltage is 4.5 V, and “reference value = 3.0 V”.

If Vi> reference value, the first CPU 11
Proceeds to step 102, and determines in the subsequent voltage switching process that the applied voltage Vp is to be changed in the order of negative side → positive side with respect to the normal voltage (air-fuel ratio detecting voltage).
If Vi ≦ reference value, the first CPU 11 proceeds to step 103, and in the subsequent voltage switching processing, changes the applied voltage Vp from the positive side to the negative side with respect to the normal voltage (air-fuel ratio detection voltage). It is determined that the voltage is changed in order.

In short, for example, when Vi = 2V (when step 101 is NO), when the voltage Vp is swept to the negative side,
The voltage Vo immediately saturates at the lower limit (1.5 V) of the output capability of the operational amplifier OP1, and the voltage Vo cannot be completely swept, so that the element resistance cannot be accurately obtained. Conversely, for example, when Vi = 4 V (when step 101 is YES), when the voltage Vp is swept to the positive side, the voltage Vo immediately saturates at the upper limit value (4.5 V) of the output capability of the operational amplifier OP1. As a result, the element resistance cannot be determined accurately. On the other hand, by determining the sweep direction of the voltage Vp according to the comparison between the voltage Vi and the reference value as described above, it is possible to prevent the voltage Vi from sticking to the upper limit value or the lower limit value.

Thereafter, the first CPU 11 executes step 1
At 04, the voltage Vo input to the terminal Ch1 is detected, and the detected voltage Vo is stored as Vo (t1). Further, a voltage Vi input to the terminal Ch2 is detected,
The detected voltage Vi is stored as the above-mentioned Vi (t2).

Subsequently, the first CPU 11 executes step 1
At 05, the voltage Vp of the terminal DAC1 is swept to the positive side or the negative side. At this time, if the determination in step 101 is affirmative, the voltage Vp is swept to the negative side,
If 01 is negatively determined, the voltage Vp is swept to the positive side. Then, the first CPU 11 proceeds to step 10
In step 6, the current time is stored as "Ta". The time Ta is a time corresponding to the time t3 in FIG.

Thereafter, the first CPU 11 executes step 1
At 07, it waits for a predetermined time. This waiting time is a time corresponding to the time T1 in FIG. 8, and is 135 μs in the present embodiment.

After a lapse of 135 μs, the first CPU 11
Is the voltage Vi input to the terminal Ch2 in step 108.
Is detected, and the detected voltage Vi is referred to as the aforementioned Vi (t4).
To be stored. Further, the voltage V input to the terminal Ch1
o is detected, and the detected voltage Vo is referred to as Vo (t
5) is stored.

Thereafter, the first CPU 11 executes step 1
At 09, the voltage Vp of the terminal DAC1 is changed to the opposite side to the sweeping direction. At this time, if step 101 is determined to be positive, the voltage Vp is changed to the positive side, and if step 101 is determined to be negative, the voltage Vp is changed to the negative side. Then, the first CPU 11 stores the current time as “Tb” in step 110. The time Tb is a time corresponding to the time t6 in FIG.

Further, the first CPU 11 executes step 11
In step 1, the admittance value Y is calculated from the voltage change amount ΔV and the current change amount ΔI using the following equation (2).

[0057]

(Equation 2) Equation (2) basically agrees with equation (1), but in equation (2), the calculation of the shunt resistance is omitted, assuming that the shunt resistance is corrected by LSB conversion described later. I have.

Thereafter, the first CPU 11 executes step 1
In step 12, the calculated admittance value Y is subjected to LSB conversion to obtain an admittance count value Y '.
The LSB-converted admittance count value Y ′ is transmitted to the second CPU 12 in step 3. At this time, while the processing of steps 104 to 111 is performed with 2 bytes, in step 113, 1-byte data subjected to LSB conversion is transmitted by DMA communication.

Thereafter, the first CPU 11 executes step 1
At 14, the time difference (Tb-T) between the time obtained by subtracting the stored time Tb from the current time and the stored times Tb and Ta.
a) to determine whether or not the current time-Tb> Tb-Ta holds.

When the determination at step 114 is affirmative, the first CPU 11 proceeds to step 115, returns the voltage Vp of the terminal DAC1 to the original normal voltage (air-fuel ratio detection voltage), and thereafter executes this routine once. finish. In FIG. 8, an affirmative determination is made in step 114 at time t7.

Next, the second CPU 12 in the on-vehicle ECU 1
Will be described with reference to the flowchart of FIG. The processing in FIG. 5 is executed, for example, at a cycle of 128 ms.

When the second CPU 12 starts the processing shown in FIG. 5, first, in step 201, a target element temperature Tm (about 700 ° C. in the present embodiment) is set. Also, the second
CPU 12 of the first CPU 1
The admittance count value Y ′ is received from 1.

Thereafter, the second CPU 12 executes step 2
At 03, it is determined whether or not the received admittance count value Y 'is equal to or smaller than a predetermined value Ka. The predetermined value Ka is A
This is a threshold value for determining whether the / F sensor 30 is active or inactive, and is, for example, a count value corresponding to an element temperature of about 625 ° C.

If Y ′ ≦ Ka (Step 203: YE
In the case of S), the second CPU 12 proceeds to step 204, and converts the admittance count value Y 'into the element temperature Ty by interpolating the conversion map of FIG. For example, during warm-up at the start of the engine, the A / F sensor 30 is inactive, so that the element temperature Ty is calculated from the conversion map of FIG.

On the other hand, if Y ′> Ka (step 203)
Is NO), the second CPU 12 proceeds to step 205
The element temperature Ty is calculated by approximating the linear equation (linear line) shown in FIG. That is, in FIG. 6, the region where the admittance count value Y ′ exceeds Ka (element temperature> 625
In the temperature range (° C.), the element temperature is estimated from the admittance count value Y ′ using two linear expressions having different slopes.

More specifically, the second CPU 12 determines in step 205 whether the admittance count value Y 'is equal to or less than a predetermined value Kc. The predetermined value Kc is a predetermined temperature (for example, about 800 ° C.) within the activation temperature range of the A / F sensor 30.
Is a count value corresponding to. If Y ′ ≦ Kc (if Step 205 is YES), the second CPU 12 proceeds to Step 206 and calculates the element temperature Ty according to the following proportional relational expression (3).

Ty = a × Y ′ + b (3) In the equation (3), a and b are constants. Also, Y '> Kc
(When step 205 is NO), the second CPU
12 proceeds to step 207 to calculate the element temperature Ty according to the following proportional relational expression (4).

Ty = c × Y ′ + d (4) c and d in the above equation (4) are constants. That is, in FIG. 6, the element temperature is obtained by the above equation (3) in the area where the admittance count value = Ka to Kc, and the element temperature is obtained by the above equation (4) in the area where the admittance count value> Kc. Becomes

After calculating the element temperature Ty as described above, the second
CPU 12 determines whether the element temperature Ty is equal to or higher than the target element temperature Tm in step 208. If Ty ≧ Tm, the second CPU 12 determines that the heating of the sensor element unit 32 by the heater 33 is unnecessary, and stops driving the heater 33 in step 209, and thereafter terminates this routine once. If Ty <Tm, the second CPU 12 determines that the heater 33 needs to heat the sensor element section 32, drives the heater 33 in step 210, and then terminates this routine once.

In the present embodiment, the processing of steps 101 to 109 in FIG. 4 corresponds to the voltage switching means, and the processing of step 111 corresponds to the admittance value calculating means. Steps 203 to 2 in FIG.
Step 07 corresponds to the element temperature detecting means.

According to the present embodiment described in detail above, the following effects can be obtained. (A) In the present embodiment, when detecting the element resistance of the A / F sensor 30, the admittance value Y is calculated as Y = ΔI / ΔV from the voltage change amount ΔV and the current change amount ΔI. Then, based on the calculated admittance value Y, the element temperature Ty is calculated.
Was detected.

Thus, the relationship of the conventional device where the impedance value and the element temperature are not in a proportional relationship (the relationship of FIG. 10).
Unlike the admittance value Y having a proportional relationship with the element temperature, the element resistance can be grasped. Then, by detecting the element temperature from the admittance value Y, the detection accuracy is improved. More specifically, as shown in FIG. 9, even when the admittance count value deviates by one count, the deviation amount of the element temperature is small, and the detection error of the element temperature can be suppressed. Temperature deviation amount is 1
℃).

(B) In the active temperature range of the A / F sensor 30, the element temperature is detected by utilizing the fact that the admittance value and the element temperature are in a proportional relationship. Therefore, the element temperature can be accurately detected particularly in the active temperature range of the A / F sensor 30 where the detection accuracy is required. In the present embodiment, the heater control can be satisfactorily performed while the sensor 30 is in the active state, and the air-fuel ratio detection and the air-fuel ratio feedback control can be performed with high accuracy.

(C) The element temperature is detected based on the admittance value by using a linear equation (straight line) having a different slope for each of a plurality of divided active temperature regions of the A / F sensor 30. By converting the admittance value to the element temperature using the linear equation in this way, the calculation load can be reduced as compared with the case where the element temperature is calculated from the conversion map. Further, by selectively using a plurality of straight lines having different inclinations, the accuracy of element temperature detection is further improved.

(D) In a temperature range lower than the active temperature range of the A / F sensor, the element temperature is detected by interpolation of map data. In this case, by using a conversion map,
Although there is a concern about an increase in the calculation load, the use of the map is limited to a temporary period until the sensor is activated, so that the conventional problem does not continue during normal use after activation.

(E) Using the central voltage of the output capability of the operational amplifier OP1 as a reference value, the CPU 11 of the shunt resistor R3
If the voltage value on the input side (input voltage Vi of the terminal Ch2) exceeds the reference value, the applied voltage at the time of detecting the element resistance is switched to the negative side. The applied voltage at that time was switched to the positive side. In this case, by switching the applied voltage in a direction having a margin with respect to the center voltage (reference value) of the output capability of the operational amplifier OP1, sticking of the applied voltage to the lower limit or the upper limit can be prevented, and the element resistance (admittance) can be reduced. Value) can be prevented from deteriorating.

By determining the direction of voltage switching according to the voltage Vi, the first CPU 11 can perform an appropriate switching operation without knowing whether the air-fuel ratio is rich or lean at that time. At this time, since the voltage Vi is determined by the capability of the operational amplifier OP1, the voltage switching operation is not affected by the individual difference of the A / F sensor 30 or the change with time.

(F) In this embodiment, the on-board ECU
A two-CPU system is constructed in one, an admittance value is calculated by the first CPU 11, and an element temperature corresponding to the admittance value is detected by the second CPU 12. Also, the first and second CPUs 11 and 12 are communicably connected to each other by DMA communication, and the first CPU 11 transmits the operation data (admittance) to the second CPU 12 with a smaller number of bytes than when the admittance value is calculated. Count value). According to such a configuration, the information of the element resistance can be transmitted with a small number of bytes while maintaining the accuracy of a necessary portion. Therefore, the effect that the load in the DMA communication can be greatly reduced can be obtained.

The embodiment of the present invention can be realized in the following modes other than the above. In the above embodiment, according to the relationship of FIG. 6, the activation temperature range of the A / F sensor 30 (element temperature>
The admittance value was converted to the element temperature using two linear equations (straight lines) having different slopes within the range of 625 ° C.). One or more linear equations may be used. Also, in a region lower than the activation temperature range of the A / F sensor 30, linear approximation may be performed instead of the conversion map of FIG. Conversely, it is also possible to use a conversion map in the activation temperature range as in the conventional device.

The detection of the element temperature from the admittance value may be limited to only the activation temperature range of the A / F sensor 30. In other words, in a region other than the active temperature region, the requirement for element temperature detection accuracy is relatively low, and a conventional method for detecting element temperature from an impedance value is acceptable. So, A
In the active temperature range of the / F sensor 30, the element temperature is detected from the admittance value, and in other than the active temperature range of the sensor 30, the element temperature is detected from the impedance value.

In the above embodiment, the detected element temperature Ty
Heater 33 is turned on according to the result of comparison between
Although the N / OFF control was performed, this configuration is changed. For example,
The deviation between the detection element temperature and the target element temperature is obtained, and the heater power supply amount (duty ratio control amount, heater power amount, etc.) is controlled so as to eliminate this deviation. That is, feedback control of the element temperature is performed. In this case, the control accuracy of the element temperature feedback is improved by applying the present invention.

In the above embodiment, the admittance value (element resistance) is calculated by the first CPU 11 and the second CP
The element temperature corresponding to the admittance value was detected by U,
It is also possible for either one of the CPUs to execute both the calculation of the admittance value and the detection of the element temperature.

In the above embodiment, the element temperature Ty of the A / F sensor 30 is detected and the detection result is used for heater control. In addition, the detection result of the element temperature Ty is used for the A / F sensor 30. It may be used for deterioration determination. For example, the characteristics of the element temperature with respect to the amount of current supplied to the heater are stored in advance, and the degree of deterioration of the sensor is determined according to the change in the characteristics.

In the above-described embodiment, the cup-type A / F sensor is embodied as the limiting current type air-fuel ratio sensor, but may be embodied as a stacked A / F sensor instead. Incidentally, in the stacked A / F sensor, advantages such as excellent temperature-rise characteristics are known.

Further, the present invention can be applied to devices other than the air-fuel ratio detecting device using the A / F sensor. That is, NO
A gas concentration sensor that can detect gas concentration components such as x, HC, and CO is used, and the present invention can be applied to a gas concentration detection device for detecting the concentration of a specific component by the sensor. Also in the other gas concentration detection devices, by using the same method as in the above embodiment, the detection accuracy of the element temperature is improved, and the detection accuracy of the gas concentration is improved.

[Brief description of the drawings]

FIG. 1 is an electrical configuration diagram showing an outline of a vehicle-mounted ECU according to an embodiment of the invention.

FIG. 2 is a cross-sectional view illustrating a configuration of an A / F sensor.

FIG. 3 is a VI characteristic diagram of an A / F sensor.

FIG. 4 is a flowchart showing an element resistance detection routine.

FIG. 5 is a flowchart showing a heater driving routine.

FIG. 6 is a diagram showing a relationship between an element temperature and an admittance count value.

FIG. 7 is a diagram showing an element temperature calculation map.

FIG. 8 is a time chart showing a Vo voltage waveform and a Vi voltage waveform at the time of element temperature detection.

FIG. 9 is a diagram showing a relationship between an element temperature and an admittance count value.

FIG. 10 is a diagram showing a relationship between an element temperature and an impedance count value.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... In-vehicle ECU, 11 ... 1st CPU which comprises voltage switching means and admittance value calculation means, 12 ... 2nd CPU which comprises element temperature detection means, 30 ... A / F sensor as gas concentration sensor, 32 ... Sensor element part, 33 ... Heater, 34 ... Solid electrolyte layer, R3 ... Shunt resistor, OP
1 ... Operational amplifier.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-11-201935 (JP, A) JP-A-11-211692 (JP, A) JP-A-8-278279 (JP, A) JP-A Sho 57- 192856 (JP, A) JP-A-59-230154 (JP, A) JP-A-61-122556 (JP, A) JP-A-61-132851 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/41 G01N 27/409 G01N 27/419 G01N 27/00-27/24

Claims (10)

(57) [Claims] The present invention is applied to a gas concentration sensor that outputs a current signal according to a concentration of a specific component in a gas to be detected in accordance with application of a voltage to a sensor element having a solid electrolyte, and temporarily applies a voltage applied to the sensor element. Voltage switching means for selectively switching to a positive side or a negative side; admittance value calculating means for calculating an element resistance as an admittance value from a voltage change amount and a current change amount associated with the voltage switching; based on the calculated admittance value An element temperature detecting means for detecting the element temperature. 2. An element temperature detecting device for a gas concentration sensor according to claim 1, wherein said element temperature detecting means detects an element temperature based on said calculated admittance value in an activation temperature range of said gas concentration sensor. 3. The gas concentration sensor according to claim 1, wherein said element temperature detecting means detects the element temperature by utilizing that the calculated admittance value and the element temperature are in a proportional relationship. Element temperature detector. 4. An active temperature region of the gas concentration sensor is divided into a plurality of regions, and the element temperature detecting means uses an approximate straight line having a different slope for each of the divided regions, based on the calculated admittance value. The device temperature detecting device for a gas concentration sensor according to claim 1 or 2, wherein the device temperature is detected. 5. An element temperature detecting device for a gas concentration sensor according to claim 1, wherein said element temperature detecting means detects the element temperature by interpolating map data in a temperature range lower than an activation temperature range of said gas concentration sensor. 6. An element temperature detecting device for a gas concentration sensor according to claim 1, wherein said element temperature detecting means detects the element temperature by interpolating the map data in a non-linear region on the coordinates of the element temperature and the admittance value. 7. A shunt resistor having one end connected to the gas concentration sensor and the other end connected to a signal processing unit for processing a sensor signal, wherein the shunt resistor receives a voltage applied to the sensor element, and And an operational amplifier having an output terminal connected to the signal processing unit side of the device, wherein the voltage switching unit sets a reference value according to the operational amplifier, and the signal processing unit side of the shunt resistor. When the voltage value exceeds the reference value, the applied voltage at the time of detecting the element temperature is switched to the negative side. When the voltage value at the signal processing unit side of the shunt resistor is lower than the reference value, the applied voltage at the time of detecting the element temperature is changed to the positive side. The device temperature detecting device for a gas concentration sensor according to claim 1, wherein the switching is made to 8. An element temperature detecting device according to claim 1, wherein
The voltage switching means and the admittance value detecting means.
A first CPU for receiving the admittance value calculated by the first CPU, and a second CPU having the element temperature detecting means for detecting the element temperature based on the received admittance value. Characteristic element temperature detecting device for gas concentration sensor. 9. The device temperature detecting device according to claim 8, wherein the first CPU is configured to control the admittance value calculating means.
That admittance value of the element temperature detecting apparatus for a gas concentration sensor for transmitting operation data to the second CPU with a smaller number of bytes than during operation. 10. The element temperature detecting device according to claim 8, wherein the first and second CPUs are connected to each other so as to be able to communicate with each other by DMA communication. .