JPH0815215A - Oxygen content determining device - Google Patents

Abstract

PURPOSE:To continuously execute element temperature determination until an oxygen sensor is activated to quickly perform activation by heater control based on the element temperature in an oxygen content determining device. CONSTITUTION:At the time of determining the temperature of a sensor main body 20, a micro-computer 70 determines the temperature of the sensor main body 20 by a detected current of a current detecting circuit 50 when the sensor main body 20 is negative-biased by a bias control circuit 40. The temperature determination is continued until an oxygen sensor S is activated, and according to the temperature, a heater 26 is controlled by a heating control circuit 80 to quickly activate the oxygen sensor S. After activation, immediately after the temperature determination, the sensor main body 20 is positive-biased by the bias control circuit 40, and limiting current after convergence is detected by a current flowing through the sensor main body 20 by positive bias by the micro-computer 70 to determine the air-fuel ratio. Ail The above air-fuel ratio determination and temperature determination are alternately repeated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration determination device for determining the air-fuel ratio in the exhaust gas of an internal combustion engine, that is, the oxygen concentration, and in particular, it determines the oxygen concentration by utilizing a limiting current type oxygen sensor. The present invention relates to an oxygen concentration determination device suitable for.

[0002]

2. Description of the Related Art Conventionally, in this type of oxygen concentration determination device, as shown in, for example, Japanese Patent Laid-Open No. 163556/1984, the internal resistance of a limiting current type oxygen sensor changes with temperature. And that the current-voltage characteristic that specifies the temperature of the oxygen sensor, that is, the internal resistance passes through the origin, the oxygen sensor is positively biased for a first period by a positive voltage, while it is second biased by a negative voltage. Negatively biased during the first and second periods, the current flowing through the oxygen sensor is detected, the oxygen concentration is detected based on the detected current in the first period, and the detected current in the second period is detected. Based on this, the internal resistance of the oxygen sensor is detected. Then, by heating the oxygen sensor so that the detected internal resistance becomes almost constant,
The air-fuel ratio is stably determined based on the above-described detected oxygen concentration after temperature control with high accuracy so that the oxygen sensor is maintained in the active region.

Further, as shown in Japanese Patent Publication Nos. 1-28905 and 1-25419, attention is paid to the fact that the internal resistance and the temperature of the oxygen sensor have a one-to-one correspondence. By detecting the internal resistance, calculating the voltage applied to the oxygen sensor according to this detected value, and applying the voltage to the oxygen sensor based on this calculation, the operating temperature range and oxygen concentration measurable range are restricted. remove.

[0004]

However, the detected air-fuel ratio before the oxygen sensor is activated is not always reliable, and it is also unrelated to the drivability immediately after the start of the internal combustion engine, so that it is intentionally unclear. It is not necessary to accurately detect the air-fuel ratio, but rather it is more important to raise the element temperature to the activation temperature quickly by controlling the heater.

Therefore, in order to cope with such a situation, the present invention forcibly continues to apply a negative voltage until the oxygen sensor is activated, detects the element temperature, and controls the heater to quickly activate the element. The purpose is to raise the temperature and measure the oxygen concentration (air-fuel ratio) accurately in a short time after the start of operation.

[0006]

To solve the above problems, in the present invention, as illustrated in FIG. 1, a limiting current type oxygen sensor and an activation judging means for judging whether the oxygen sensor is activated or not. When the activation determining means determines that the oxygen sensor has been activated, a voltage applying means for applying a positive voltage to the oxygen sensor and switching to a negative voltage for a predetermined period and applying the positive voltage, and the activation determining means Positive voltage application sustaining means for continuously applying a positive voltage to the oxygen sensor by the voltage applying means until it is determined that the oxygen sensor is activated, and current detecting means for detecting a current flowing through the oxygen sensor by applying the voltage. An element temperature detecting means for detecting an element temperature of the oxygen sensor based on the detected current when the negative voltage is applied to the oxygen sensor for a predetermined period. The oxygen concentration determining means for determining the oxygen concentration based on the detected current when the positive voltage is applied to the oxygen sensor, the heater for heating the oxygen sensor, and the element temperature detecting means An object is to provide an oxygen concentration determination device including a heating control unit that controls heating of the heater based on the element temperature.

[0007]

By configuring the present invention as described above, the positive voltage application sustaining means continues to apply the positive voltage to the oxygen sensor by the positive voltage application sustaining means until the activation determining means determines that the oxygen sensor is activated, The element temperature of the oxygen sensor is detected by the element temperature detecting means based on the detected current when the voltage is applied. Based on the element temperature detected by the element temperature detection means, the heating control means controls the heating of the heater to quickly raise the element temperature to the activation temperature, and then the activation determination means determines that the oxygen sensor is activated. , Applying a positive voltage to the oxygen sensor and switching to a negative voltage for a predetermined period of time, and applying the positive voltage to the oxygen sensor to determine the oxygen concentration based on the detected current when the positive voltage is applied to the oxygen sensor, The element temperature of the oxygen sensor is detected by the element temperature detecting means based on the detected current when the voltage is applied for a predetermined period.

[0008]

【Example】

[First Embodiment] A first embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows an example of an oxygen concentration determination device according to the present invention applied to an internal combustion engine 10. The oxygen concentration determination device is provided with a limiting current type oxygen sensor S, and this oxygen sensor S is attached inside an exhaust pipe 11 extending from an engine body 10a of the internal combustion engine 10. The oxygen sensor S is composed of a sensor body 20 and a cover 30 having a U-shaped cross section, and the sensor body 20 has a mounting hole formed in a part of the peripheral wall of the exhaust pipe 11 at the base end thereof. It is fitted in the portion 11 a and extends toward the inside of the exhaust pipe 11.

The sensor body 20 has a diffusion resistance layer 21 having a cup-shaped cross section, and the diffusion resistance layer 21 is fitted into the mounting hole portion 11a of the exhaust pipe 11 at the opening end portion 21a thereof. ing. The diffusion resistance layer 21 is formed by a plasma spraying method using ZrO ₂ or the like. Further, the sensor body 20 has a solid electrolyte layer 22, and the solid electrolyte layer 22 is formed of an oxygen ion conductive oxide sintered body in a cup-shaped cross section, and an exhaust gas side electrode having a cup-shaped cross section. It is evenly fitted to the inner peripheral wall of the resistance diffusion layer 21 via the layer 23, and the atmosphere-side electrode layer 24 is uniformly fixed to the inner surface of the solid electrolyte layer 22 in a cup-shaped cross section. In this case, the exhaust side electrode layer 23 and the atmosphere side electrode layer 24 are
In both cases, a precious metal having a high catalytic activity such as platinum is formed sufficiently porous by chemical plating or the like. The area and the thickness of the exhaust-side electrode layer 23 is a 10 to 100 mm ² and 0.5~2.0μ about, whereas, the area and the thickness of the atmosphere-side electrode layer 24 is 10 mm ² or more And 0.5
It is about 2.0 μ.

The sensor body 20 thus constructed generates a concentration electromotive force at the stoichiometric air-fuel ratio point and a limiting current corresponding to the oxygen concentration in the lean region from the stoichiometric air-fuel ratio point. In such a case, the limiting current corresponding to the oxygen concentration is determined by the area of the exhaust gas side electrode layer 23, the thickness of the diffusion resistance layer 21, the porosity and the average pore diameter. Further, although the sensor body 20 can detect the oxygen concentration with a linear characteristic, a high temperature of about 650 ° C. or higher is required to activate the sensor body 20, and the sensor body 20 has a high temperature. Since the active temperature range of the internal combustion engine is narrow, the active region cannot be controlled by heating only the exhaust gas of the internal combustion engine. Therefore, the heating control of the heater 26 described later is utilized. In the region richer than the stoichiometric air-fuel ratio, carbon monoxide (CO) which is unburned gas
Changes almost linearly with respect to the air-fuel ratio, and a limiting current corresponding to this is generated.

The voltage-current characteristic of the sensor body 20 with the temperature of the sensor body 20 as a parameter will now be described. The current-voltage characteristic is proportional to the oxygen concentration (air-fuel ratio) detected by the oxygen sensor S. It is shown that the relationship between the current flowing into the solid electrolyte layer 22 of the main body 20 and the voltage applied to the solid electrolyte layer 22 is linear. Then, when the sensor body 20 is in the active state at the temperature T = T1, a stable state is shown by the characteristic graph L1 as shown by the solid line in FIG. 3 (B). In such a case, the characteristic graph L1
The straight line portion parallel to the voltage axis V specifies the limit current of the sensor body 20. Then, the increase / decrease in the limit current corresponds to the increase / decrease in the air-fuel ratio (that is, lean / rich). When the temperature T of the sensor body 20 is at T2 lower than T1,
The current-voltage characteristic is specified by the characteristic graph L2 as shown by the broken line in FIG. In such a case, the straight line portion parallel to the voltage axis V of the characteristic graph L2 specifies the limiting current of the sensor main body 20 at T = T2, and this limiting current substantially matches the limiting current according to the characteristic graph L1.

Then, in the characteristic graph L1, if a positive applied voltage Vpos is applied to the solid electrolyte layer 22 of the sensor body 20, the current flowing through the sensor body 20 becomes the limiting current Ipo.
s (see point P1 in FIG. 3B). Further, if a negative applied voltage Vneg is applied to the solid electrolyte layer 22 of the sensor body 20, the current flowing through the sensor body 20 does not depend on the oxygen concentration but is proportional to the temperature only. Becomes Therefore, by controlling the heating of the heater 26 by utilizing the current Ineg at this time, the internal resistance of the sensor body 20 can be made substantially constant and the sensor body 20 can be maintained in the active state.

Further, the sensor body 20 has a heater 26, which is housed in the atmosphere-side electrode layer 24, and the heat energy generated by the heater 26 causes the atmosphere-side electrode layer 2 to be heated.
4. The solid electrolyte layer 22, the exhaust gas side electrode layer 23 and the diffusion resistance layer 21 are heated. In such a case, the heater 26 has a heat generation capacity sufficient to activate the sensor body 20.
The cover 30 covers the sensor main body 20 and is fitted into a part of the peripheral wall of the exhaust pipe 11 at the opening thereof, and a small hole 31 is provided in a part of the peripheral wall of the cover 30. Thirty
Is provided so that the outside of the container communicates with the inside of the cover 30. As a result, the cover 30 is attached to the sensor body 20.
The sensor body 2 while preventing direct contact with exhaust gas of
Secure 0 insulation.

As shown in FIG. 2, the oxygen concentration determination device also includes a bias control circuit 40. The bias control circuit 40 includes a positive bias DC power supply 41, a negative bias DC power supply 42, and a changeover switch. It is configured by the circuit 43. The DC power supply 41 has its negative electrode connected to one end of the exhaust gas side electrode layer 23 via a lead wire 41a, while the DC power supply 42 has its positive electrode connected to the exhaust gas via a lead wire 41a. It is connected to one end of the side electrode layer 23. In the first switching state, the changeover switch circuit 43 connects only the positive electrode of the DC power supply 41 to the input terminal 51 of the current detection circuit 50, while in the second switching state, the negative side of the DC power supply 42 is connected. Only the side electrode is connected to the input terminal 51 of the current detection circuit 50, and is connected to the atmosphere side electrode layer 24 from the input terminal 51, the current detection circuit 50, and the lead wire 42a. Therefore, when the changeover switch circuit 43 is in the first changeover state, the DC power supply 41 positively biases the solid electrolyte layer 22 to cause a current to flow in the solid electrolyte layer 22 in the positive direction.
On the other hand, when the change-over switch circuit 43 is in the second change-over state, the DC power supply 42 negatively biases the solid electrolyte layer 22 to cause a current to flow in the solid electrolyte layer 22 in the negative direction. In this case, the terminal voltages of the DC power supplies 41 and 42 correspond to the above-mentioned applied voltages Vpos and Vneg, respectively.

The current detection circuit 50 detects a current flowing from the atmosphere-side electrode layer 24 of the sensor body 20 to the changeover switch circuit 43 or a current flowing in the opposite direction, that is, a current flowing in the solid electrolyte layer 22, and A-D Output to the converter 60. The AD converter 60 digitally converts the detected current from the current detection circuit 50 and outputs it to the microcomputer 70. The microcomputer 70 executes the computer program in cooperation with the AD converter 60 according to the flowchart shown in FIG. 4, and during this execution, the heating control circuit 80 and the fuel injection control device (hereinafter referred to as EFI). The arithmetic processing required to drive and control 90 is performed. However, the computer program described above is stored in advance in the ROM of the microcomputer 70.
Further, the heating control circuit 80 is the microcomputer 70.
The heating of the heater 26 is controlled according to the element temperature of the oxygen sensor S under the control of. The EFI 90 is controlled by the microcomputer 70 under the control of the internal combustion engine 1
Fuel injection control is performed according to internal combustion engine information such as zero exhaust gas amount, rotational speed, intake air flow rate, intake pipe negative pressure and cooling water temperature.

In the first embodiment constructed as described above, after the microcomputer 70 starts executing the computer program in step 100 according to the operation of the internal combustion engine 10 in accordance with the flowchart of FIG. It is assumed that the execution is repeated. First, in step 141, it is determined whether or not the oxygen sensor S is in the active state. The determination condition is that the element temperature of the oxygen sensor S has reached a temperature sufficient to activate the oxygen sensor S, and a time tA sufficient to activate the oxygen sensor S has elapsed after the internal combustion engine was started. (Here, the time tA may be a constant value, but it is preferable to store and set in the ROM of the microcomputer 70 such a value that the activation determination time becomes longer as the cooling water temperature of the internal combustion engine becomes lower. ), Or both are satisfied, it is determined that the oxygen sensor S is in an active state and stable. Then, if "YES" is determined in step 141, the process proceeds to step 101, and after the temperature detection cycle is variably set based on the warm-up state and the operating state of the internal combustion engine, the next step 102 is step 10
In step 1, it is determined whether or not the temperature detection cycle is variably set, and if it is not the temperature detection cycle, the determination of "NO" is repeated in step 102.

In such a state, the microcomputer 70 executes the computer program shown in FIG.
Of Step 111 and Step 123, and in Step 111, the positive applied voltage V to the sensor body 20 is applied.
The positive bias command required to apply pos is output to the changeover switch circuit 43 of the bias control circuit 40. Here, the applied voltage Vpos may be a constant value, but as shown in FIG. 3B, the applied voltage Vpos necessary for detecting the limiting current changes according to the element temperature of the oxygen sensor S and the oxygen concentration. The applied voltage Vpos is changed according to the element temperature and the oxygen concentration (when the element temperature is low, the applied voltage Vpos is higher than when it is high).
Is set to a high value and the oxygen concentration is high (air-fuel ratio is lean)
Sometimes it is preferable to set the applied voltage Vpos to a higher value than when it is thin (the air-fuel ratio is rich). Then, the change-over switch circuit 43 enters the first change-over state in response to the positive bias command from the microcomputer 70, and connects the positive side electrode of the DC power supply 41 to the input terminal 51 of the current detection circuit 50. Therefore, the current Ipos from the DC power supply 41 flows as a limiting current through the current detection circuit 50, the conductor 42a, the atmosphere side electrode 24, the solid electrolyte layer 22, the exhaust gas side electrode 23 and the conductor 41a.

Next, the current detection circuit 50 detects the inflow current Ipos, and the AD converter 60 digitally converts the detected inflow current Ipos and outputs it to the microcomputer 70. Then, the microcomputer 70 inputs the same conversion current Ipos in step 123 and sets it as the reduction end current Iposa, and in step 124,
Based on the oxygen concentration-limit current data shown in (B), the oxygen concentration, that is, the air-fuel ratio is determined according to the reduction end current Iposa, that is, the limit current. However, the oxygen concentration-limit current data shown in FIG. 5B is data for specifying the linear relationship between the oxygen concentration in the exhaust gas at the temperature T = T1, that is, the air-fuel ratio and the limit current of the sensor body 20. R
Pre-stored in the OM. When the air-fuel ratio is determined in this way, the microcomputer 70 executes the step 1
At 25, the arithmetic processing required for the fuel injection control of the EFI 90 is performed in consideration of the determined air-fuel ratio. Therefore, EFI90
Performs fuel injection control to the internal combustion engine 10 based on the same calculation process.

In such a state, step 101
Based on the determination of the temperature detection cycle set in step 2, the microcomputer 70 determines “YES” in step 102, and applies negative voltage Vneg to the sensor body 20 in step 112. The required negative bias command is output to the changeover switch circuit 43 of the bias control circuit 40 (see FIG. 5A). Then, the changeover switch circuit 43 becomes the second changeover state in response to the negative bias command from the microcomputer 70, and the negative side electrode of the DC power supply 42 is connected to the input terminal 51 of the current detection circuit 50.
Connect to. Therefore, the current Ineg from the DC power source 42
(Refer to the solid line in FIG. 5A) indicates the conductive wire 41a, the exhaust gas side electrode 23 of the sensor body 20, the solid electrolyte layer 22,
It starts flowing through the atmosphere-side electrode 24, the conducting wire 42a, and the current detecting circuit 50.

After the arithmetic processing in step 112 as described above, the microcomputer 70 waits for a predetermined time t1 in step 103 to wait for the predetermined time t1.
Determine if it has passed. In such a case, the predetermined time t1 is defined as follows. The current Ineg is the sensor body 2
After the negative bias to 0, it increases exponentially as shown by the solid line and the broken line in FIG. Therefore, as in the conventional case, wait until the current Ineg is saturated and wait until the current In
If eg is detected, the subsequent air-fuel ratio determination timing will also be delayed. Therefore, the value Inega of the one period during the process of increasing the current Ineg without waiting for the saturation of the current Ineg.
Is utilized to estimate the saturation current Inegs of the current Ineg at the same time. As a result, it can be seen that the air-fuel ratio determination time becomes earlier. Therefore, an appropriate time until the time when the change tendency of the current Ineg after the negative bias to the sensor body 20 is kept relatively high is selected as the predetermined time t1 and stored in the ROM of the microcomputer 70 in advance.

If "NO" is determined in the step 103, the process proceeds to a step 104, and in this step 104, it is determined whether or not the change amount of the intake pipe pressure or the intake air amount is a predetermined value or more, that is, the engine is transient. It is determined whether or not When it is determined to be “NO” in step 104, the process returns to step 103 and this process is repeated. If "YES" is determined in step 104, the process proceeds to the next step 105, the negative bias command is stopped in this step 105, and then the process proceeds to step 120.

When the time waiting in step 103 is completed, the microcomputer 70, in step 114, converts the conversion current Ineg from the AD converter 60.
Is set as the current Inega, and the same current I
According to nega, the saturation current Inegs is estimated based on the transient phenomenon equation representing the relationship between the current Ineg and the applied voltage Vneg.
In such a case, the transient phenomenon equation is stored in the ROM of the microcomputer 70 in advance, with the negative bias timing of the sensor body 20 as an initial condition. Thereafter, in step 116, the microcomputer 70 determines the temperature of the sensor body 20 based on the estimated saturation current-temperature characteristic data according to the estimated saturation current Inegs. However, the above-mentioned estimated saturation current-temperature characteristic data is stored in advance in the ROM of the microcomputer 70 as data representing a direct proportional relationship between the estimated saturation current | Inegs | and the temperature of the sensor body 20.

When the temperature of the sensor main body 20 is determined in this way, the microcomputer 70 makes a determination in step 1
In step 17, an arithmetic process is performed to control the heating of the heater 26 so as to maintain the determination temperature in step 116 at the temperature T1 (see the characteristic graph L1). Therefore, the heating control circuit 80 controls the heating of the heater 26 based on the heating control calculation process of the microcomputer 70. This allows
Even if the temperature of the sensor body 20 is temporarily lowered, it quickly returns to the temperature T1.

Therefore, the microcomputer 70
At step 120, it is judged if the air-fuel ratio is in a stable judgment possible state. When this determination condition satisfies the activation determination condition of the oxygen sensor S in step 141 described above,
It is determined that the air-fuel ratio is in a stable determination condition. Then, in step 120, it is determined to be "YES" based on the determination that the air-fuel ratio can be stably determined, and the computer program proceeds to step 121 and thereafter. Then, in step 121, the microcomputer 70 outputs to the bias control circuit 40 a positive bias command required to apply the positive applied voltage Vpos to the sensor body 20. Then, the bias control circuit 40 applies the applied voltage Vpos from the DC power supply 41 to the sensor body 20 as described above. This means that the applied voltage Vpos is applied to the sensor body 20 immediately after the elapse of the predetermined period t1. Therefore, the current Ipos from the DC power supply 41
However, immediately after the elapse of the predetermined period t1, the flow starts as a limiting current through the conductor 41a, the exhaust gas side electrode 23 of the sensor body 20, the solid electrolyte layer 22, the atmosphere side electrode 24, the conductor 42a and the current detection circuit 50. In other words, the current Ineg flowing through the sensor body 20 as shown in FIG.
Immediately after the elapse of the predetermined period t1, as shown by the solid line in the figure, the current is inverted and rises to become the current Ipos, and thereafter it starts to decrease exponentially.

When the arithmetic processing in step 121 is completed as described above, the microcomputer 70
However, in the next step 122, a predetermined time (t11-t1)
Wait for the time only (see FIG. 5A). However, t
11 is from the time when the current Ineg begins to flow as described above,
It represents the time until the current Ipos, which started to flow immediately after the elapse of the predetermined period t1, ends exponentially decreasing. In such a case, the predetermined time (t11-t1) is determined based on the following grounds.

First, the current Ineg is as shown in FIG.
The applied voltage Vpo changes exponentially as shown by the solid line in (A) and saturates as shown by the broken line in FIG.
s is applied to the sensor body 20 (see the broken line in FIG. 5A) for positive bias, and the applied voltage Vpos is applied to the sensor body 20 immediately after the elapse of a predetermined period t1 as in the present embodiment ( A comparison will be made between the case of positive bias and the solid line shown in FIG. However, the current Ine in the conventional case
The time required for saturation of g is represented by t2 as shown in FIG.

In such a case, the value at which the current Ipos due to the application of the applied voltage Vpos finishes decreasing is almost the same in both the conventional case and the first embodiment based on the physical phenomenon unique to the sensor body 20. is there. Therefore, if the time until the time when the current Ipos exponentially ends in the conventional case is represented by t22 as shown in FIG. 5A, the time when the current Ipos starts to flow in the case of the first embodiment ( Figure 5 (A)
The solid line in FIG. 4) is earlier than the time when the current Ipos starts to flow (see the broken line in FIG. 5A) in the conventional case by a time (t2-t1). In the case of the first embodiment, the time when the current Ipos finishes decreasing becomes earlier than the time when the current Ipos finishes decreasing in the conventional case.
Furthermore, the time when the current Ipos starts to flow in the case of the first embodiment corresponds to one time during the rising of the current Ineg, while the time when the current Ipos starts to flow in the conventional case ends the rise of the current Ineg. It corresponds to the time. This way,
The oxygen concentration accumulated near the exhaust gas side electrode layer 23 during the negative bias period becomes smaller than that in the conventional case. Therefore, the rising peak level of the current Ipos becomes low,
Further, the time constant when the same current Ipos decreases becomes smaller, and decreases more rapidly. The degree of this effect depends on the amount of electric charge carried during the negative bias period. That is, the shorter the t1 and the smaller the amount of electric charge, the smaller the above two items become and the shorter t11 becomes. Therefore, the time from the beginning of the flow of the current Ineg to the end of the reduction of the current Ipos in the conventional case is shown in FIG.
When represented by t22 as shown in (A), (t22-t1
1) only faster. Therefore, a predetermined time (t11-t1) is set and stored in the RM of the microcomputer 70 in advance.

When the time waiting in step 122 is completed, the microcomputer 70 receives the conversion current Ipos from the AD converter 60 immediately after the elapse of the predetermined time t11 in step 123, and the decrease end current is received. Ip
Then, in step 124, the oxygen concentration, that is, the air-fuel ratio is determined according to the reduction end current Iposa, that is, the limiting current, based on the oxygen concentration-limit current data (see FIG. 5B). When the air-fuel ratio is determined in this manner, the microcomputer 70 performs the arithmetic processing required for the fuel injection control of the EFI 90 in step 125 in consideration of the air-fuel ratio. Therefore, the EFI 90 controls the fuel injection to the internal combustion engine 10 based on the same calculation process.

As described above, when the temperature of the sensor body 20 is determined, one period (predetermined time) before the current Ineg flowing through the sensor body 20 after the sensor body 20 is negatively biased by the applied voltage Vneg is finished. When t1 has elapsed), the saturation current I
Since the temperature of the sensor body 20 is determined by inferring negs, it is possible to quickly realize the subsequent air-fuel ratio determination possible time period.

Immediately after the elapse of the predetermined time t1, the sensor body 20 is positively biased by the applied voltage Vpos, and the time when the current Ipos flowing through the sensor body 20 is completely reduced by this positive bias, that is, the predetermined time (t11-t1). Since the air-fuel ratio is determined by the current Iposa at this time when the above condition elapses, the air-fuel ratio can be determined earlier than in the conventional case. In such a case, as described above, the rising peak level of the current Ipos in the case of the first embodiment is maintained relatively lower than the rising peak level of the current Ipos in the conventional case, and the current in the case of the present invention. Since Ipos decreases sharply compared with the current Ipos in the conventional case,
The determination of the air-fuel ratio can be made even earlier. Also, the current Ipo
The value Iposa at which s ends decreasing may be estimated during the decrease of Ipos so that the air-fuel ratio change can be known earlier.

Immediately after the internal combustion engine is started and the oxygen sensor S has not been activated yet, it is determined to be "NO" in step 141, the process proceeds to step 142, and the sensor body 20 is detected. The negative bias command required to apply the negative applied voltage Vneg is output to the changeover switch circuit 43 of the bias control circuit 40. Then, the changeover switch circuit 43 enters the second changeover state in response to the negative bias command from the microcomputer 70, and connects the negative side electrode of the DC power supply 42 to the input terminal 51 of the current detection circuit 50. Therefore, the current Ineg from the DC power source 42 (see the solid line in FIG. 5A) is
a, the exhaust gas side electrode 23 of the sensor main body 20, the solid electrolyte layer 22, the atmosphere side electrode 24, the lead wire 42a, and the current detection circuit 50 start flowing.

After the arithmetic processing in step 112 as described above, the microcomputer 70 waits for a predetermined time t33 in step 143 to wait for the predetermined time t33.
Determine if it has passed. In this case, the predetermined time t33 is set to a time (see FIG. 5A) where the current Ineg is saturated after the current Ineg is negatively biased to the sensor body 20, and the predetermined time t33 has not elapsed. In this case, it is determined that the current Ineg is not yet saturated, and the process proceeds to step 130 and ends. When it is determined in step 143 that the predetermined time t33 has elapsed, it is determined that the current Ineg is saturated and the routine proceeds to step 144, where the detected current I at that time is
After setting neg as the saturation current Inegs, step 11
Go to 6.

As a result, when the oxygen sensor S is not activated, thereafter, step 116 → step 11
After going through 7 → step 120 → step 130,
By repeating step 141 → step 142 → step 143 → step 144 ..., The element temperature of the oxygen sensor S is continuously determined based on the saturation current Inegs (sensor main body 20
However, the positive voltage is not applied to the air-fuel ratio, and therefore the air-fuel ratio is not determined.) As a result, as shown in FIG. 6, the heating control of the heater 26 is executed based on the continuously determined element temperature,
Since the element temperature can be quickly raised to the activation temperature, accurate oxygen concentration measurement can be started in a short time after the internal combustion engine is started.

In consideration of the case where it is determined in step 141 that the oxygen sensor S is activated when the element temperature of the oxygen sensor S is equal to or higher than a predetermined value, the element of the oxygen sensor S when starting the internal combustion engine is considered. The initial value of the temperature is preferably set to a low temperature when the oxygen sensor S is inactive, for example, the same value as the engine cooling water at the time of starting. [Detail 1 of Temperature Detection Cycle Variable Setting Step 101] Details of the temperature detection cycle variable setting step 101 will be described with reference to FIG. First, in step 151, after the internal combustion engine is started, it is determined whether a predetermined time ta in which the engine temperature stabilizes (or a predetermined temperature at which the element temperature stabilizes or more) is determined (here, the time ta may be a constant value, It is preferable to store in the ROM of the microcomputer 70 a value such that the stabilization determination time becomes longer as the cooling water temperature of the internal combustion engine is lower). If the predetermined time ta has not elapsed, go to step 152. Go to step 116 of FIG.
After detecting the change amount ΔT of the element temperature of the oxygen sensor S determined in step 153, the process proceeds to step 153 and, as shown in the map 1 of FIG. 8, the change amount Δ of the element temperature which is one of the engine warm-up states.
The detection period corresponding to the element temperature change amount ΔT is determined from the map 1 in which T and the detection period are stored in advance in the ROM of the microcomputer 70. This map 1 is set so that the detection cycle becomes shorter as the element temperature change amount ΔT becomes larger. If the predetermined time ta has elapsed after the start of the internal combustion engine, the routine proceeds to step 154, where the change amount ΔQ of the intake air amount Q of the internal combustion engine is detected, and then the routine proceeds to step 155 and the map 2 of FIG. As shown in, the change amount ΔQ of the intake air amount Q, which is one of the engine operating state changes,
The detection period corresponding to the change amount ΔQ of the intake air amount Q is determined from the map 2 which is stored in advance in the ROM of the microcomputer 70. The map 2 is set to have a longer detection cycle than the map 1, and the map 2 is set to have a longer detection cycle as the change amount ΔQ of the intake air amount Q increases.

As a result, after the oxygen sensor S is activated, the element temperature change amount ΔT is relatively large as shown in FIG. 9, and the element temperature change amount ΔT of the map 1 is maintained for a predetermined time ta after the start. The element temperature detection cycle corresponding to [1] is prioritized, and as the element temperature change amount ΔT increases, the element temperature detection frequency increases and the element temperature can be detected quickly by following the element temperature change. Further, since the element temperature change amount ΔT is relatively small after the elapse of the predetermined time ta after the start, the element temperature detection cycle corresponding to the change amount of the intake air amount Q in the map 2 is prioritized, and when the air-fuel ratio changes largely, The frequency of temperature detection is reduced, and it becomes possible to detect the air-fuel ratio by quickly following the change in the air-fuel ratio. The change in the heater voltage from the start of the internal combustion engine, the voltage applied to the sensor body 20, and the element temperature are As shown in 6, the result is good.

Here, in the map 1 of FIG. 8, as the warm-up state, the change amount of the cooling water temperature of the internal combustion engine may be used instead of the element temperature change amount ΔT. in this case,
In step 152 of FIG. 7, it goes without saying that instead of the element temperature change amount ΔT, the change amount of the cooling water temperature of the internal combustion engine is detected. In addition, in the map 2 of FIG.
As the operation state change amount, instead of the change amount of the intake air amount Q, the change amount ΔA / F of the air-fuel ratio A / F and the intake pipe pressure Pm.
.DELTA.Pm, the amount of change .DELTA.Ne of the engine speed Ne, the amount of change .DELTA.TAU of the fuel injection amount TAU, the amount of change of the throttle opening, and the amount of change of the vehicle speed may be used. In this case, in step 154 of FIG.
Instead of the change amount of the intake air amount Q, the change amount ΔA / F of the air-fuel ratio A / F, the change amount ΔPm of the intake pipe pressure Pm, the change amount ΔNe of the engine speed Ne, and the change amount ΔT of the fuel injection amount TAU.
Of course, any one of the AU, the change amount of the throttle opening, and the change amount of the vehicle speed may be detected.

[Temperature detection cycle variable setting step 101
Details 2 of the above] The details 2 of the temperature detection cycle variable setting step 101 will be described with reference to FIG. First, step 17
In step 1, the element temperature change amount ΔT of the oxygen sensor S is detected in the same manner as in step 152 of FIG. 7, and in the next step step 172, it is determined whether the element temperature change amount ΔT is equal to or greater than a predetermined value α. Advances to step 153, and the detection cycle is determined in the same manner as step 153 of FIG. If the element temperature change amount ΔT is less than or equal to the predetermined value, step 174
7 to detect the change amount ΔQ of the intake air amount Q of the internal combustion engine, the process proceeds to step 175 and step 155 of FIG.
The detection cycle is determined in the same manner as.

As a result, after the oxygen sensor S is activated, as shown in FIG. 11, the element temperature variation ΔT.
Is larger than the predetermined value α, the element temperature change amount Δ of the map 1
The element temperature detection cycle corresponding to T is prioritized, and as the element temperature change amount ΔT increases, the element temperature detection frequency increases, and the element temperature can be detected quickly by following the element temperature change. When the element temperature change amount ΔT becomes smaller than the predetermined value α, the element temperature detection period corresponding to the change amount of the intake air amount Q in the map 2 is prioritized, and the element temperature detection frequency decreases when the air-fuel ratio changes largely. As a result, the air-fuel ratio can be detected by quickly following the change in the air-fuel ratio.

[Second Embodiment] Next, a second embodiment will be described. In the first embodiment described above, when estimating the saturation current Inegs of the current Ineg, the value Inega of one period during the increasing process of the current Ineg was measured only once to detect Inega. In the example, the current value Inega is measured by measuring the value Inega at one time during the increase process of the current Ineg three times.
The saturation current Inegs is estimated, and by doing so, the saturation current Inegs can be estimated more accurately.

Similar to FIG. 4, FIG. 12 shows a voltage V applied to the sensor body 20 and a current I flowing through the sensor 20 at that time.
It is the figure which showed. In FIG. 12, the applied voltage V is Vpo
The current Ineg that flows when switching from s to Vneg changes exponentially as shown in the following formula 1 with the peak current value I ₀ , the saturation current value (converging current value) Inegs, and the time constant T.

[0041]

[Equation 1] Ineg = Inegs + (I ₀ −Inegs) e ^{−t / T} where peak current value I ₀ and saturation current value (convergence current value)
If Inegs and time constant T are unknowns,
In order to obtain Inegs, it is necessary to detect the detected current values at three points on the Ineg curve, Inega1, Inega2 and Inega3. Then, the detected current values of the three detected points, Ine
From ga1, Inega2, and Inega3, the solution thereof, that is, Inegs, is obtained based on the following simultaneous equations of equation 2.

[0042]

[Number 2] _{Inega1 = Inegs + (I 0 -Inegs} ) e -t1a / T Inega2 = Inegs + (I 0 -Inegs) e -t1b / T Inega3 = Inegs + (I 0 -Inegs) e -t1c / T where, Inega1 , Inega2 and Inega3 are t1a and t1b after switching the applied voltage V from Vpos to Vneg, respectively.
And the current value Ineg after t1c time. For example,
To simplify the calculation, t1a = 0, t1b = t1c-t1b
Then, by substituting these values into Equation 2 to obtain Inegs, Inegs is obtained as in the following Equation 3.

[0043]

[Equation 3] Inegs = (Inega2 ² −Inega3 · Inega1) /
(2Inega2-Inega3-Inega1) Next, the operation of the second embodiment will be described with reference to the flowchart of FIG. The second embodiment differs from the first embodiment described above in that steps 103 to 115 in FIG. 4 are replaced with steps 113a to 115 in FIG. Therefore, the description of the steps 141 to 144 and the steps 101 to 112 is the same as that of the above-described first embodiment, and the description thereof will be omitted.

After the arithmetic processing in step 112, the microcomputer 70 waits for a predetermined time t1a in step 113a. When the time waiting in step 113a is completed, the microcomputer 70 detects the current value in step 114a, and the microcomputer 70 detects the current value.
The converted current Ineg from 0 is set as the current Inega1. After that, the microcomputer 70 waits for a predetermined time t1b in step 113b. Step 113
When the time waiting in b is completed, the microcomputer 70 detects the current value in step 114b,
The converted current Ineg from the -D converter 60 is set as the current Inega2. Then, the microcomputer 70 waits for a predetermined time t1c in step 113c.

When the time waiting in step 113c is completed, the microcomputer 70 makes the step 114
At c, the current value is detected, and the converted current Ineg from the AD converter 60 is set as the current Inega3. Then, in step 115, the saturation current Ine is calculated based on the simultaneous equations of Equation 2.
Calculate gs. In such a case, the simultaneous equations of the above equation 2 are
The negative bias timing of the sensor body 20 is set as an initial condition, and is stored in the ROM of the microcomputer 70 in advance. Thereafter, in step 116, the microcomputer 70 determines the temperature of the sensor body 20 based on the saturation current-temperature characteristic data according to the saturation current Inegs obtained in step 115. Subsequent steps 117-
Since the steps up to step 130 are the same as those in the above-described first embodiment, the description thereof will be omitted.

As described above, in the second embodiment, the value Inega of one period during the increasing process of the current Ineg is measured three times to estimate the saturation current Inegs of the current Ineg. By doing this,
The saturation current Inegs can be estimated more accurately. [Other Embodiments] Incidentally, in the above-mentioned embodiments,
Although the temperature detection cycle is continuously changed based on the maps 1 and 2 of FIG. 8 before and after the stabilization of the air-fuel ratio, only two cycles are used so that the temperature detection cycle after stabilization becomes longer than that before stabilization. Alternatively, the temperature detection and the air-fuel ratio detection may be repeated at a constant cycle after the oxygen sensor S is activated without changing the temperature detection cycle before and after the stabilization of the air-fuel ratio.

Further, in the above-described embodiment, the sensor body 20 is applied with the applied voltage Vpos immediately after the elapse of the predetermined time t1.
However, the present invention is not limited to this, and the applied voltage Vpos is not limited to this but after the predetermined time t1 has elapsed and before the predetermined time t11 has elapsed.
Therefore, the sensor body 20 may be positively biased. Further, in carrying out the present invention, it is not limited to the determination of the oxygen concentration in the exhaust gas of the internal combustion engine 10,
The present invention may be applied to the determination of the oxygen concentration in each gas.

[0048]

As a result, the element temperature of the oxygen sensor is continuously detected after the operation is started until the oxygen sensor is activated, and the heating of the heater is controlled based on the detected temperature to quickly activate the element temperature. Therefore, there is an excellent effect that the oxygen concentration can be accurately measured in a short time after the operation is started.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to the description in the claims.

FIG. 2 is a block circuit diagram showing a first embodiment of the present invention.

3A is an enlarged cross-sectional view of a sensor body of the oxygen sensor of FIG. 2, and FIG. 3B is a graph showing a limiting current-voltage characteristic of the oxygen sensor with temperature as a parameter.

4 is a flowchart showing the operation of the microcomputer of FIG.

FIG. 5A is a time chart showing a waveform of a voltage applied to the sensor main body and a current flowing through the sensor main body when a negative bias and a positive bias are applied, and FIG. 5B shows a relationship between the oxygen concentration and the limiting current. It is a graph shown.

FIG. 6 is a time chart for explaining the operation of the first embodiment.

FIG. 7 is a flowchart showing details 1 of a temperature detection cycle variable setting step in the above embodiment.

FIG. 8 is a diagram showing a detection cycle map 1 for a warm-up state and a detection cycle map 2 for an operating state.

9 is a time chart used to explain the operation of FIG.

FIG. 10 is a flowchart showing details 2 of a temperature detection cycle variable setting step in the above embodiment.

11 is a time chart used for explaining the operation of FIG.

FIG. 12 is a time chart showing waveforms of a voltage applied to the sensor body and a current flowing through the sensor body when the negative bias and the positive bias are the same as in FIG.

FIG. 13 is a flowchart showing the operation of the microcomputer in the second embodiment of the present invention.

[Explanation of symbols]

 S Oxygen sensor 20 Sensor body 40 Bias control circuit 50 Current detection circuit 70 Microcomputer

Claims (10)

[Claims] 1. A limiting current type oxygen sensor, activation determining means for determining whether the oxygen sensor is activated, and the oxygen sensor when the activation determining means determines that the oxygen sensor is activated. A voltage applying unit that applies a positive voltage and switches to a negative voltage for a predetermined period of time, and a positive voltage is applied to the oxygen sensor by the voltage applying unit until the activation determining unit determines that the oxygen sensor is activated. Positive voltage application sustaining means for continuing, current detection means for detecting a current flowing in the oxygen sensor by applying the voltage, and the negative voltage based on the detected current when the negative voltage is applied to the oxygen sensor for a predetermined period. An element temperature detecting means for detecting an element temperature of the oxygen sensor, and an oxygen concentration based on the detected current when the positive voltage is applied to the oxygen sensor. An oxygen concentration determination device comprising: an oxygen concentration determination unit that determines whether the oxygen sensor is heated, a heater that heats the oxygen sensor, and a heating control unit that controls heating of the heater based on the element temperature detected by the element temperature detection unit. . 2. The activation discriminating means includes means for detecting that the element temperature detected by the element temperature detecting means has reached a temperature sufficient to activate the oxygen sensor. 1. The oxygen concentration determination device according to 1. 3. The oxygen sensor is arranged in an exhaust system of an internal combustion engine, and the activation determination means detects that a time sufficient for the oxygen sensor to be activated has elapsed after the internal combustion engine was started. The oxygen concentration determination device according to claim 1, further comprising means. 4. The oxygen concentration determination device according to claim 3, wherein the activation time is set to be longer as the temperature of the internal combustion engine is lower. 5. An element temperature stability determination means for determining whether the element temperature of the oxygen sensor is stable, and when the element temperature determination means determines that the element temperature is stable, the element temperature is not stable. The oxygen concentration determination device according to any one of claims 1 to 4, further comprising: a cycle setting unit that sets a cycle for switching to the negative voltage longer than when the determination is made. 6. The element temperature stability determining means includes means for detecting that the element temperature detected by the element temperature detecting means has reached a temperature sufficient to stabilize the element temperature. 5. The oxygen concentration determination device described in 5. 7. The element temperature stability determining means includes means for detecting that the amount of change in the element temperature detected by the element temperature detecting means is equal to or less than a value corresponding to the stabilization of the element temperature. The oxygen concentration determination device according to claim 5, including the oxygen concentration determination device. 8. The oxygen sensor is arranged in an exhaust system of an internal combustion engine, and the element temperature stability determining means detects that a sufficient time has elapsed for the element temperature to stabilize after the internal combustion engine is started. The oxygen concentration determination device according to claim 5, further comprising: 9. The oxygen concentration determination device according to claim 8, wherein the time sufficient for stabilization is set to be longer as the temperature of the internal combustion engine is lower. 10. The oxygen concentration according to any one of claims 1 to 9, further comprising applied voltage varying means for varying an applied voltage to the oxygen sensor based on the element temperature detected by the temperature detecting means. Judgment device.