JP3404892B2 - Oxygen concentration determination device - Google Patents

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, in such a configuration, since the above-described second period is uniformly repeated, even if the air-fuel ratio can be stably determined,
Only after the second period has elapsed, the air-fuel ratio cannot be determined, and the problem that the air-fuel ratio can be determined is delayed. Further, since the above-mentioned second period is repeatedly set regardless of the temperature decrease of the oxygen sensor, the application timing of the negative voltage to the oxygen sensor does not always coincide with the temperature decrease start timing of the oxygen sensor. Therefore, once the temperature of the oxygen sensor drops too much by the time the next negative voltage is applied, once the air-fuel ratio can be stably determined,
Since the oxygen sensor has a slow response to temperature, it takes a long time before the air-fuel ratio can be determined stably even if the temperature control described above is performed by applying the same negative voltage. . In such a case, the second period described above is set to the time required for the internal resistance of the oxygen sensor to stabilize, which causes a further delay in the determination period of the air-fuel ratio.

Therefore, according to the present invention, in order to deal with such a situation, the oxygen concentration determination device cannot determine the oxygen concentration by scheduling the internal resistance detection timing and the air-fuel ratio detection timing according to the degree of necessity. The purpose is to significantly reduce the time.

[0006]

To solve the above-mentioned problems, in the present invention, as illustrated in FIG. 1, a limiting current type oxygen sensor, a positive voltage is applied to the oxygen sensor, and a negative voltage is applied for a predetermined period. A voltage applying unit that switches and applies the voltage, a current detecting unit that detects a current flowing in the oxygen sensor by applying the voltage, and the negative current based on the detected current when the negative voltage is applied to the oxygen sensor for a predetermined period. Impedance detection means for detecting the DC impedance of the oxygen sensor, oxygen concentration determination means for determining the oxygen concentration based on the detected current when the positive voltage is applied to the oxygen sensor, and the timing for switching to the negative voltage It is another object of the present invention to provide an oxygen concentration determination device, which is provided with timing varying means for variably setting.

[0007]

With the above configuration of the present invention, the timing for switching the voltage applied to the oxygen sensor to the negative voltage is variably set by the timing varying means, and the temperature sensor can be operated at a low temperature when the temperature change of the oxygen sensor is small. The detection interval can be lengthened to lengthen the period in which a positive voltage is applied to the oxygen sensor for determining the oxygen concentration.

[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 (DC impedance) of the sensor body 20, that is, the element temperature is made substantially constant and the sensor body 20 is maintained in the active state. It becomes possible.

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 covers 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. At the present stage, it is assumed that the oxygen sensor S is in an active state and stable. And step 10
At 1, the temperature detection cycle is variably set based on the warm-up state and the operating state of the internal combustion engine, and then at step 102, it is determined whether or not the temperature detection cycle is variably set at step 101. If not, 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
In step 120, "YES" is determined based on the determination that the air-fuel ratio is stable and the computer program proceeds to step 121 and subsequent steps. 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 ends exponentially decreasing in the conventional case is represented by t22 as shown in FIG.
In the case of the embodiment, the time when the current Ipos starts to flow (see FIG. 5).
(See the solid line in the figure in (A)) is the current Ipos in the conventional case.
The time (t2-t1) is earlier than the time when the flow starts (see the broken line in FIG. 5A), and correspondingly, the time when the current Ipos in the case of the first embodiment finishes decreasing. But,
This is earlier than the time when the current Ipos in the conventional case ends decreasing. Further, 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 increase of the current Ineg. It corresponds to the time. By doing so, the oxygen concentration accumulated near the exhaust gas side electrode layer 23 during the negative bias period becomes smaller than in the conventional case.
For this reason, the rising peak level of the current Ipos becomes lower, and the time constant when the current Ipos decreases becomes smaller, and the current Ipos decreases more rapidly. The degree of these two effects depends on the amount of electric charge carried during the negative bias period. That is, t1
The shorter the value of T2 and the smaller the amount of electric charge, the smaller the above two items become and the shorter t11 becomes. Therefore, the current I in the conventional case
The time from the beginning of the neg flow to the end of the decrease of the current Ipos is represented by t22 as shown in FIG.
(T22-t11) faster. Therefore, a predetermined time (t11
-T1) is set and stored in the ROM 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.

In the first 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. [Second Embodiment] Next, a second embodiment will be described. In the first embodiment described above, the saturation current Inegs of the current Ineg
In estimating the above, the value Inega was detected by measuring the value Inega at one point during the increasing process of the current Ineg only once, but in the second embodiment, the value Inega at one period during the increasing process of the current Ineg is detected. This is because the saturation current Inegs of the current Ineg is estimated by measuring three times, and by doing so, the saturation current Inegs can be estimated more accurately.

Similar to FIG. 5, FIG. 6 is a diagram showing a voltage V applied to the sensor body 20 and a current I flowing through the sensor 20 at that time. In FIG. 6, the current Ineg that flows when the applied voltage V is switched from Vpos to Vneg is represented by the following equation 1 which has a peak current value I ₀ , a saturation current value (converging current value) Inegs, and a time constant T. Changes exponentially.

[0033]

[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, ie, Inegs, is obtained based on the following simultaneous equations.

[0034]

[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.

[0035]

[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 113 to 115 in FIG. 4 are replaced with steps 113a to 115 in FIG.
Therefore, the description of steps 100 to 112 is the same as that of the first embodiment described above, and the description thereof is 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 300 are the same as those in the 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. [Details 1 of Temperature Detection Cycle Variable Setting Step 101] Next, 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, and if the predetermined time ta has not elapsed, the step Proceeding to 152, after detecting the amount of change ΔT of the element temperature of the oxygen sensor S determined in step 116 of FIG. 4 or FIG. 7, the routine proceeds to step 153, as shown in map 1 of FIG. Element temperature change amount ΔT which is one of them
The detection period corresponding to the element temperature change amount ΔT is determined from the map 1 which is 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 step 1
55, the map 2 in which the change amount ΔQ of the intake air amount Q, which is one of the engine operating state changes, and the detection cycle are stored in advance in the ROM of the microcomputer 70 as shown in map 2 of FIG. Therefore, the change amount Δ of the intake air amount Q
The detection cycle corresponding to Q is determined. The map 2 is set so that the detection cycle is longer than that of the map 1, and the larger the change amount ΔQ of the intake air amount Q is,
The detection cycle is set to be long. As a result, as shown in FIG. 10, the element temperature change period ΔT is relatively large, and the element temperature detection period corresponding to the element temperature change amount ΔT of the map 1 is prioritized during the predetermined time ta after the start, so that the element temperature change is performed. The larger the amount ΔT, the more frequently the element temperature is detected, and the element temperature can be detected quickly by following the change in the element temperature. In addition, after a lapse of a predetermined time ta after starting, the element temperature change amount Δ
Since T is relatively small, 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 a lot, the element temperature detection frequency decreases and the air-fuel ratio changes quickly. The air-fuel ratio can be detected by following the above.

Here, in the map 1 of FIG. 9, 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,
Of course, in step 152 of FIG. 8, instead of the element temperature change amount ΔT, the change amount of the cooling water temperature of the internal combustion engine is detected. Also, in 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 temperature detection cycle variable setting step 101 will be described with reference to FIG. First, step 16
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. 8, and in step 162, the provisional determination t1a of the detection cycle is detected in the same manner as in step 153 of FIG. At 163, the change amount ΔQ of the intake air amount Q is detected in the same manner as step 154 in FIG.
In step 64, the provisional determination t2a of the detection cycle is detected in the same manner as in step 155 of FIG.
The final detection period to is determined by obtaining the average value of the provisionally determined values t1a and t2a at 62 and 164. This makes it possible to determine the element temperature detection cycle that always considers both the warm-up state and the engine state change.

[Detail 3 of Temperature Detection Cycle Variable Setting Step 101] Details 3 of the temperature detection cycle variable setting step 101 will be described with reference to FIG. First, step 171
Then, the element temperature change amount ΔT of the oxygen sensor S is calculated in step 1 of FIG.
Similarly to step 52, it is determined in the next step 172 whether the element temperature change amount ΔT is equal to or larger than the predetermined value α. If it is equal to or larger than the predetermined value α, the process proceeds to step 173, and the same as step 153 of FIG. To determine the detection cycle. If the element temperature change amount ΔT is less than or equal to the predetermined value, the routine proceeds to step 174, 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 175, similar to step 155 of FIG. To determine the detection cycle.

As a result, as shown in FIG. 13, while the element temperature change amount ΔT is larger than the predetermined value α, the element temperature detection period corresponding to the element temperature change amount ΔT in the map 1 is prioritized,
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.

[Additional Embodiment 1 of Prohibition of Negative Bias when Air-Fuel Ratio Changes] Next, when it is predicted that the air-fuel ratio of the internal combustion engine suddenly changes, the element temperature detection of the oxygen sensor S is prohibited and the air-fuel ratio of An additional example 1 in which detection is performed with priority will be described with reference to FIGS. 14 and 15. FIG. 14 shows a flowchart added after step 101 in FIG. 4, and in step 181, the load consisting of at least one of the throttle opening of the internal combustion engine, the intake pipe pressure, and the intake air amount fluctuates by a predetermined value or more. If it is determined that the air-fuel ratio does not change abruptly, the process proceeds to step 102 in FIG. 4 to enable the element temperature to be detected, but it is determined that the load changes by a predetermined value or more. If so, it is predicted that the air-fuel ratio will change suddenly, and the routine proceeds to step 182, where as shown in FIG. 15, the stable timing from the change of the load, especially the throttle opening, to the stabilization of the limiting current of the air-fuel ratio sensor S. Estimate t20 and a change period α in which the limit current of the air-fuel ratio sensor S is actually changing with a delay after the throttle opening suddenly changes. Here, as for the stable timing T20 and the change period α, the predetermined value preset by the adaptive test of the internal combustion engine is the ROM of the microcomputer 70.
The stable timing t20 and the change period α may be constant values, but the optimum value is variably set according to the engine parameters such as the load variation amount and the load magnitude. preferable.

In the next step 183, it is judged whether (stable timing t20-change period α) has elapsed. If not, the limit current of the air-fuel ratio sensor S still changes after the throttle opening suddenly changes. 4 is assumed to be a response delay period, and the element temperature can be detected in step 102 of FIG. 4, but if (stable timing t20−change period α) has elapsed, the process proceeds to step 184 and the change period α is set. To determine if has passed. If it is determined in step 184 that the change period α has passed, the element temperature can be detected assuming that the change in the air-fuel ratio is small.
If it is determined that the air temperature has not changed, the process proceeds to step 185, and the negative bias is prohibited to prohibit the detection of the element temperature.
Go to 0 and prioritize detection of the air-fuel ratio.

According to this embodiment, the detection of the element temperature is prohibited only during the change period α during which the throttle current is changed abruptly and then the limit current of the air-fuel ratio sensor S is actually changed. . [Additional Embodiment 2 Inhibiting Negative Bias When Air-Fuel Ratio Changes] Next, when it is predicted that the air-fuel ratio of the internal combustion engine suddenly changes,
An additional example 2 in which the element temperature detection of the oxygen sensor S is prohibited and the air-fuel ratio detection is performed with priority will be described with reference to FIGS. 16 and 17. FIG. 16 shows step 10 of FIG.
1 shows a flowchart added after 1.
As compared with the fourth embodiment, step 182a is used instead of step 182, and the stable timing t20 and the air-fuel ratio sensor S after the throttle opening changes as shown in FIG.
The delay timing t21 until the actual air-fuel ratio at the arrangement position of is changed is estimated, and instead of step 183, step 183a is used to determine whether the delay timing t21 has elapsed, and instead of step 184, In step 184a, it is determined whether (stable timing t20-delay timing t21) has elapsed. Here, the delay timing t21 is also a predetermined value preset by the adaptation of the internal combustion engine by the microcomputer 7.
The delay timing t21 may be a fixed value, but it is preferable to variably set the optimum value in accordance with the engine parameter such as the load variation amount or the load size.

According to this embodiment, as shown in FIG. 17, the (stable timing t20−
During the period of the delay timing t21), the negative bias is prohibited and the element temperature detection is prohibited, but the air-fuel ratio detection is prioritized accordingly. [Additional Embodiment 3 of Prohibiting Negative Bias When Air-Fuel Ratio Changes] Next, when it is predicted that the air-fuel ratio of the internal combustion engine suddenly changes,
An additional embodiment 3 in which the element temperature detection of the oxygen sensor S is prohibited and the air-fuel ratio is detected with priority will be described with reference to FIGS. 18 and 19. FIG. 18 shows step 10 of FIG.
1 shows a flowchart added after 1.
In contrast to the fourth embodiment, step 182b is used instead of step 182 to estimate only the stable timing t20, and step 183b is used instead of steps 183 and 184 to change the throttle opening degree. As shown in FIG. 19, it is determined whether or not the stable timing t20 has elapsed, and during this stable timing t20, the negative bias is prohibited and the element temperature detection is prohibited.

[Other Embodiments] In addition, in the additional embodiments 1 to 3 of prohibiting the negative bias when the air-fuel ratio changes, the timing variable means is configured in combination with the temperature detection cycle variable setting step 101. Variable cycle setting step 1
No. 01 is used, positive bias and negative bias are alternately executed at regular time intervals, and the additional examples 1 to 3 of prohibiting the negative bias when the air-fuel ratio changes are applied to the timing variable means. It may be configured.

Further, in carrying out the present invention, not only the determination of the oxygen concentration in the exhaust gas of the internal combustion engine 10 but also the
The present invention may be applied to the determination of the oxygen concentration in each gas.

[0049]

As a result, in a state where the temperature change of the oxygen sensor is small, the temperature detection interval can be lengthened to lengthen the time during which the positive voltage is applied to the oxygen sensor for determining the oxygen concentration. In the oxygen concentration determination device, there is an excellent effect that the time during which the oxygen concentration cannot be determined can be greatly shortened.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to the description of 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 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. 7 is a flowchart showing the operation of the microcomputer in the second embodiment of the present invention.

FIG. 8 is a flow chart showing details 1 of a temperature detection cycle variable setting step in each of the embodiments.

FIG. 9 is a diagram showing a detection cycle map 1 for a warm-up state and a detection cycle map 2 for an operating state.

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

FIG. 11 is a flowchart showing the details 2 of the temperature detection cycle variable setting step in each of the embodiments.

FIG. 12 is a flowchart showing details 3 of a temperature detection cycle variable setting step in each of the embodiments.

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

FIG. 14 is a flow chart showing an additional embodiment 1 of prohibition of negative bias when changing the air-fuel ratio, which is added to FIG.

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

FIG. 16 is a flowchart showing an additional example 2 of addition of prohibition of negative bias when changing the air-fuel ratio, which is added to FIG. 4.

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

FIG. 18 is a flowchart showing an additional embodiment 3 of prohibition of negative bias when changing the air-fuel ratio, which is added to FIG. 4.

FIG. 19 is a time chart for explaining the operation of FIG.

[Explanation of symbols]

S oxygen sensor 20 sensor body 40 Bias control circuit 50 current detection circuit 70 Microcomputer

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasutaka Nakamori 1-1, Showa-cho, Kariya city, Aichi Japan Denso Co., Ltd. (56) Reference JP-A-57-192849 (JP, A) JP-A-6- 27078 (JP, A) JP 58-178248 (JP, A) JP 61-132851 (JP, A) JP 57-192852 (JP, A) JP 59-163556 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 27/41

Claims (15)

(57) [Claims] 1. A limiting current type oxygen sensor, voltage applying means for applying a positive voltage to the oxygen sensor and switching to a negative voltage for a predetermined period, and detecting a current flowing through the oxygen sensor by applying the voltage. Current detecting means, impedance detecting means for detecting a DC impedance of the oxygen sensor based on the detected current when the negative voltage is applied to the oxygen sensor for a predetermined period, and the positive voltage is applied to the oxygen sensor. The oxygen concentration determination device comprising: an oxygen concentration determination unit that determines the oxygen concentration based on the detected current during the operation; and a timing variable unit that variably sets the timing of switching to the negative voltage. 2. The oxygen concentration determination device according to claim 1, wherein the timing changing means includes means for changing the timing of switching to the negative voltage according to the DC impedance detected by the impedance detecting means. 3. The oxygen concentration determination device according to claim 2, wherein the timing for switching the negative voltage is set so that the period becomes longer as the amount of change in the DC impedance decreases. 4. The timing varying means includes means for changing the timing of switching to the negative voltage according to the oxygen concentration detected by the oxygen concentration detecting means.
Alternatively, the oxygen concentration determination device described in 2. 5. The oxygen concentration determination device according to claim 4, wherein the timing of switching the negative voltage is set so that the period becomes longer when the oxygen concentration detected by the oxygen concentration detection means changes. 6. The oxygen sensor is arranged in an exhaust system of an internal combustion engine, and comprises operating state detecting means for detecting an operating state of the internal combustion engine, wherein the timing varying means changes the operating state detected by the operating state detecting means. 2. The oxygen concentration determination device according to claim 1, further comprising means for changing the timing of switching to the negative voltage in accordance therewith. 7. The operating state detecting means includes a transient operating state detecting means for detecting a transient operating state of the internal combustion engine, and the transient operating state detecting means detects the transient operating state at a timing of switching the negative voltage. The oxygen concentration determination device according to claim 6, wherein the period is set to be long when the oxygen concentration is determined. 8. The operating state detecting means includes a warming-up state detecting means for detecting a warming-up state of the internal combustion engine, and an operating state change detecting means for detecting a change in the operating state of the internal combustion engine, wherein the timing variable Means for varying the timing for switching the negative voltage in accordance with the engine warm-up state detected by the warm-up state detection means, and in accordance with a change in the operating state detected by the operating state change detection means 7. The oxygen concentration determination device according to claim 6, further comprising means for varying the timing of switching to a negative voltage. 9. The timing varying means preferentially determines a timing for switching the negative voltage according to an engine warm-up state for a predetermined period after the start of the internal combustion engine, and after the predetermined period, the operating state change detecting means. 9. The oxygen concentration determination device according to claim 8, further comprising means for preferentially determining the timing of switching to the negative voltage in accordance with the change in the operating state detected by. 10. The timing varying means preferentially determines the timing of switching the negative voltage according to the engine warm-up state when the change in the engine warm-up state is a predetermined value or more, and the engine warm-up state is determined. 9. The oxygen concentration determination device according to claim 8, further comprising means for preferentially deciding the timing of switching to the negative voltage according to the change in the operating state when the change is less than a predetermined value. Wherein said warm-up state detection means, one of claims 8-10 comprising more or the temperature detection means for detecting the temperature of the element temperature detection means for detecting the element temperature of the oxygen sensor and the internal combustion engine The oxygen concentration determination device according to any one of claims. 12. The oxygen sensor is arranged in an exhaust system of an internal combustion engine, and the timing variable means prohibits application of the negative voltage to prohibit application of the negative voltage when it is expected that a change in an air-fuel ratio of the internal combustion engine will be large. Claims 1 to 1 including a means.
1. The oxygen concentration determination device according to any one of 1. 13. The negative voltage application prohibiting means detects a load fluctuation of the internal combustion engine when the load fluctuation is equal to or more than a predetermined value, and an empty space of the internal combustion engine after detecting that the load fluctuation is equal to or more than the predetermined value. ratio is a predetermined time to stabilize, claim and a timer means for inhibiting application of the negative voltage 12
The oxygen concentration determination device described. 14. The oxygen sensor includes a stable timing estimating means for estimating a timing from when the load fluctuation changes by a predetermined value or more until the oxygen concentration determined by the oxygen concentration determining means becomes stable. Delay timing estimating means for estimating a delay timing until the air-fuel ratio at the arrangement position delays from the load change and actually changes, and prohibits the application of the negative voltage during the period from the delay timing to the stable timing. 14. The oxygen concentration determination device according to claim 13 , further comprising prohibition determination means for performing the determination. 15. The oxygen sensor, wherein the timer means estimates a timing from when the load fluctuation changes by a predetermined value or more until the oxygen concentration determined by the oxygen concentration determination means stabilizes, and the oxygen sensor. Period estimating means for estimating a period during which the output of the output is actually changing after being delayed from the load change, and prohibiting the application of the negative voltage during the changing period from a time point before the changing period from the stable timing. 14. The oxygen concentration determination device according to claim 13 , further comprising prohibition determination means for performing the determination.