JP2001133429A - Method for recalibrating offset of onboard nox sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recalibrating an offset of an onboard NOX sensor without the danger of an early decrease of a power of an onboard battery and of igniting a fuel remaining unburnt in a gas exhaust system. SOLUTION: When supply of a fuel into a combustion chamber of a driving automobile engine 10 is stopped, an oxygen concentration in an exhaust gas discharged to a gas exhaust system 102 becomes not smaller than 20%. An output voltage of an onboard NOX sensor 10 when this state is maintained for 0.5 second or more, preferably one second or more, more preferably 2 seconds or more is made an output voltage of 'NOX concentration = 0'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an offset recalibration method for an in-vehicle NO _X sensor, and more particularly, to NO _{X in} exhaust gas discharged from a driving automobile engine.
The present invention relates to an offset recalibration method for an in-vehicle NO _X sensor that recalibrates an offset of an in-vehicle NO _X sensor under a situation where the concentration becomes zero.

[0002]

To measure the concentration of NO _X in the exhaust gas discharged from an automobile engine, vehicle NO _X sensor is installed in the gas exhaust system of the automobile engine.

[0003] NO _X concentration can be determined from the value of the output voltage of the vehicle NO _X sensor. That is, for example, the output voltage of a certain type of in-vehicle NO _X sensor has a minimum value when the NO _X concentration is 0, and when the NO _X concentration increases, the output voltage increases accordingly. .

[0004] Information on the level of the output voltage of the on-vehicle NO _X sensor, that is, the information on the concentration of the NO _X concentration is sent to an engine electronic control unit (hereinafter referred to as ECU). When the output voltage of the on-vehicle NO _X sensor rises and exceeds a specified threshold value, the ECU determines that the NO _X concentration in the exhaust gas has exceeded the allowable upper limit, and the ECU determines that the NO _X concentration in the exhaust gas has not reached the combustion chamber of the automobile engine. Control is performed to reduce the fuel supply amount.

[0005]

However, in recent years,
Possible to further reduce the NO _X emissions from automobile engine from the viewpoint of environmental protection has been studied. For this reason, a vehicle-mounted NO _X sensor is required to accurately indicate the NO _X concentration even when the NO _X concentration is extremely low, specifically, around 0 to 10 ppm.

[0006] Of course, the in-vehicle N against a variety of NO _X concentration
The output voltage of the _OX sensor is measured before being installed in the gas exhaust system. That is, at the time when installed in the gas exhaust system of an automobile, a deviation between the measured NO _X concentration and the actual NO _X concentration by vehicle NO _X sensor (offset)
There is no. However, when the measurement of the NO _X concentration by the in-vehicle NO _X sensor is repeatedly performed in association with the repeated driving of the automobile, the output voltage value of the in-vehicle NO _X sensor when the NO _X concentration is 0 becomes However, the output voltage does not always coincide with the output voltage when the NO _X concentration measured before installation is zero. In other words, the offset occurs, and although the actual NO _X concentration is 0, −5 to 5
The output voltage corresponds to a concentration of about ppm. This offset causes a very large error when measuring the concentration around 0 to 10 ppm, and hinders accurate measurement of the concentration.

To avoid such inconvenience, so-called zero point correction (offset recalibration) may be performed. That is, the vehicle engine is stopped and the N
After O _X concentration becomes 0, considered it may be defined as the output voltage indicated by the vehicle NO _X sensor when its output voltage in NO _X concentration is 0.

However, when re-calibrating the offset of the on-vehicle NO _X sensor by the method described above,
The following problems are caused. That is, when performing the measurement of gas concentration by the sensor, it is necessary to raise the temperature of the gas detecting portion of the sensor, in order to raise the temperature of the vehicle NO _X sensor, said vehicle N the vehicle battery as a power supply
O _X must be energized to the sensor. Such discharge of the vehicle-mounted battery while the vehicle engine is stopped causes early deterioration of the performance of the vehicle-mounted battery. Furthermore, when the temperature of the vehicle NO _X sensor in a state of stopping the automobile engine, there is concern that unburned fuel remaining in the gas discharge system is ignited.

Therefore, the "fuel supply stop" issued by the ECU
Is received by the on-vehicle NO _X sensor,
It is conceivable to perform re-calibration of the offset of O _X sensor. However, in this case, if the supply of fuel is restarted immediately thereafter, there is a disadvantage that the actual NO _X concentration in the gas discharge system does not become zero. Therefore, performing the re-calibration of the offset of the in-vehicle NO _X sensor in such a situation causes a situation where the offset is further increased.

The present invention has been made to solve the above-mentioned problem, and can be carried out while the vehicle engine is being driven. Therefore, the performance of the vehicle-mounted battery is not reduced at an early stage and unburned. It is an object of the present invention to provide a method for recalibrating an offset of an in-vehicle NO _X sensor which does not have to worry about igniting fuel.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a method of measuring a measured NO _X concentration and an actual NO _X concentration generated in an in-vehicle NO _X sensor installed in a gas exhaust system of an automobile engine. a the offset is the offset recalibration method of vehicle NO _X sensor recalibration during driving of the automobile engine, the exhaust gas in the gas discharge system by the fuel supply to the combustion chamber of the motor vehicle engine is stopped When the state in which the oxygen concentration is 20% or more is maintained for a predetermined time, the measured NO _X concentration value of the in-vehicle NO _X sensor is set to 0.

[0012] Thus, since the re-calibration of the offset of the vehicle NO _X sensor is performed during driving of an automobile engine, the vehicle battery is effected it is charging. Therefore, since the vehicle-mounted battery is not excessively discharged, the performance of the vehicle-mounted battery does not deteriorate early.
Unburned fuel is discharged to the outside together with the exhaust gas, and does not remain in the gas discharge system. Therefore, unburned fuel does not ignite in the gas discharge system.

The predetermined time is preferably 0.5 seconds or more. It is more preferably at least 1 second, further preferably at least 2 seconds.

[0014] In this case, recalibration of the offset, the signal "fuel supply stop" the engine electronic control unit is issued to when the fuel supply to the combustion chamber of an automotive engine is stopped vehicle NO _X sensor received It is preferable to do it later. Thus, for example, when the oxygen concentration while NO _X is discharged by incomplete combustion of the fuel rises, since no re-calibration of the offset of the vehicle NO _X sensor is performed, the vehicle NO _X sensor The offset can be reliably re-calibrated.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a vehicle-mounted NO _{X according} to the present invention
A preferred embodiment of a sensor offset re-calibration method will be described in detail with reference to the accompanying drawings.

First, the installation position of the on-vehicle NO _X sensor will be described with reference to FIG.

[0017] As shown in FIG. 1, vehicle NO _X sensor 10 is installed in the gas exhaust line 102 connected to the gas exhaust port of an automobile engine 100. That is,
This is the gas exhaust system 102 is interposed the first catalyst device 104a and the second catalyst device 104b for decomposing NO _X, vehicle NO _X sensor 10, the gas outlet side of the second catalytic device 104b is set up. That is, the vehicle-mounted NO _X sensor 10 is for measuring the concentration of NO _X discharged without being decomposed by the first catalyst device 104a and the second catalyst device 104b.

Here, the configuration of the on-vehicle NO _X sensor 10 will be described in detail.

As shown in FIGS. 2 and 3, this on-vehicle NO _X sensor 10 includes, for example, six sheets of solid electrolytes 12a to 12f made of ceramics using an oxygen ion conductive solid electrolyte such as ZrO _2. From the bottom, the first substrate layer 12a, the second substrate layer 12b, the first spacer layer 12
c, first solid electrolyte layer 12d, second spacer layer 12
e, having the sensor element 14 configured by being laminated as the second solid electrolyte layer 12f.

Between the second substrate layer 12b and the first solid electrolyte layer 12d, there is provided a space (a reference gas introduction space 16) into which a reference gas such as air is introduced, for example. , The upper surface of the second substrate layer 12b and the first
Of the spacer layer 12c. A first chamber 18 for adjusting the partial pressure of oxygen in the exhaust gas is provided between the lower surface of the second solid electrolyte layer 12f and the upper surface of the first solid electrolyte layer 12d. A second chamber 20 for finely adjusting the partial pressure and for measuring the concentration of NO _{X in} the gas to be measured (exhaust gas) is formed.

[0021] Then, the space portion 22 to the front end portion of the in-vehicle NO _X sensor 10, the second spacer layer 12e
Is formed, and a front end opening of the space portion 22 is provided with a gas introduction port 24.
Is configured. Also, the space 22 and the first chamber 18
Are communicated via the first diffusion-controlling unit 26 and the first chamber 1
The second chamber 20 is communicated with the second chamber 20 via a second diffusion control section 28.

Here, the first and second diffusion control sections 26
And 28 provide a predetermined diffusion resistance to the exhaust gas introduced into the first chamber 18 and the second chamber 20, respectively, and in the example of FIG. It is formed as a vertically elongated slit having a cross-sectional area. Both of these vertically long slits are formed substantially at the center in the width direction of the second spacer layer 12e.

In addition, a porous body made of ZrO ₂ or the like is filled and arranged in a slit constituting the second diffusion-controlling portion 28 so that the diffusion resistance of the second diffusion-controlling portion 28 is equal to the first diffusion control. It may be made to be larger than the diffusion resistance of the rate limiting section 26. It is preferable that the diffusion resistance of the second diffusion control part 28 is larger than that of the first diffusion control part 26, but there is no problem if it is small.

Then, the atmosphere in the first chamber 18 is reduced through the second diffusion-controlling section 28 to a level below the predetermined diffusion resistance.
It will be introduced into the chamber 20.

In the space 22, firstly, particles (soot, oil burned matter, etc.) generated in the gas to be measured in the external space are the first.
Is intended to function as a clogging prevention portion for avoiding that clogging in the vicinity of the inlet of the chamber 18, it is possible to measure the NO _X components with higher accuracy.

A substantially rectangular porous cermet electrode (for example, a cermet of Pt.ZrO ₂ containing 1% of Au) is formed on the entire lower surface of the second solid electrolyte layer 12f which forms the first chamber 18. An inner pump electrode 30 formed of the second solid electrolyte layer 12
An outer pump electrode 32 is formed on a portion of the upper surface of f corresponding to the inner pump electrode 30, and the inner pump electrode 30, the outer pump electrode 32, and a second pump electrode 32 sandwiched between these two electrodes 30 and 32. 2 solid electrolyte layer 1
At 2f, an electrochemical pump cell, that is, a main pump cell 34 is formed.

A desired control voltage (pump voltage) Vp is applied between the inner pump electrode 30 and the outer pump electrode 32 in the main pump cell 34 through an external variable power supply 36.
1 and the outer pump electrode 32 and the inner pump electrode 3
By passing the pump current Ip1 in the positive direction or the negative direction during zero, oxygen in the atmosphere in the first chamber 18 is pumped to the external space, or oxygen in the external space is discharged to the first space.
It can be pumped into the chamber 18.

A reference electrode 38 is formed on a portion of the lower surface of the first solid electrolyte layer 12d that is exposed to the reference gas introduction space 16, and the inner pump electrode 30, the reference electrode 38, and the second Solid electrolyte layer 12f, second spacer layer 12e, and first solid electrolyte layer 12d
Thus, an electrochemical sensor cell, that is, a control oxygen partial pressure detection cell 40 is formed.

This control oxygen partial pressure detection cell 40 is
Based on the oxygen concentration difference between the atmosphere in the chamber 18 and the reference gas (air) in the reference gas introduction space 16, the first electromotive force is generated between the inner pump electrode 30 and the reference electrode 38, and the first The oxygen partial pressure of the atmosphere in the chamber 18 can be detected.

The detected oxygen partial pressure value is used for feedback control of the variable power supply 36. Specifically, the oxygen partial pressure of the atmosphere in the first chamber 18 is changed to the oxygen partial pressure in the next second chamber 20. The feedback control system 42 for the main pump has a predetermined value low enough to control the pressure.
Through this, the pump operation of the main pump cell 34 is controlled.

The feedback control system 42 operates between the outer pump electrode 32 and the inner pump electrode 30 so that the difference between the potential of the inner pump electrode 30 and the potential of the reference electrode 38 (detection voltage V1) becomes a predetermined voltage level. Pump voltage Vp1
Has a circuit configuration for feedback-controlling. In this case, the inner pump electrode 30 is grounded.

Therefore, the main pump cell 34 pumps or pumps oxygen out of the exhaust gas introduced into the first chamber 18 by an amount corresponding to the level of the pump voltage Vp1. Then, by repeating the series of operations, the oxygen concentration in the first chamber 18 is feedback-controlled to a predetermined level. In this state,
The pump current Ip1 flowing between the outer pump electrode 32 and the inner pump electrode 30 depends on the oxygen concentration in the exhaust gas and the first chamber 18.
Shows the difference from the control oxygen concentration, and can be used for measuring the oxygen concentration in the exhaust gas.

The porous cermet electrodes forming the inner pump electrode 30 and the outer pump electrode 32 are P
The inner pump electrode 30 disposed in the first chamber 18 in contact with the exhaust gas has a reduced ability to reduce NO components, or is made of a metal such as t and a ceramic such as ZrO ₂ , or It is necessary to use a material having no reducing ability, for example, a compound having a perovskite structure such as La ₃ CuO ₄ , a metal having low catalytic activity such as Au and a ceramic cermet, or a metal having low catalytic activity such as Au and a Pt group. It is preferable that the cermet is made of metal and ceramic. Further, Au is used for the electrode material.
When an alloy of Pt and Pt group metal is used, it is preferable that the amount of Au to be added is 0.03 to 35 vol% of the entire metal component.

Further, apart from in the vehicle NO _X sensor 10, of the upper surface of the first solid electrolyte layer 12d, an upper surface forming the second chamber 20, and the second diffusion rate-determining section 28 A detection electrode 50 composed of a porous cermet electrode having a substantially rectangular shape in a plane is formed on the portion thus formed, and the third diffusion-controlling portion 5 is formed so as to cover the detection electrode 50.
2 is formed. The detection electrode 50, the reference electrode 38, and the first solid electrolyte layer 12d form an electrochemical pump cell, that is, a measurement pump cell 54.

The detection electrode 50 is made of a porous cermet made of a metal capable of reducing NO _X and zirconia as a ceramic, thereby reducing NO _X existing in the atmosphere in the second chamber 20. Besides functioning as a NO _X reduction catalyst, between the reference electrode 38 by a constant voltage Vp2 is applied through a DC power source 56, pumped oxygen in the atmosphere in the second chamber 20 to the reference gas-introducing space 16 It can be put out. The pump current Ip2 flowing by the pump operation of the measurement pump cell 54
Is detected by the ammeter 68.
Further, the pump current Ip2 is converted into a voltage and taken out as an output voltage Va.

The constant-voltage (DC) power supply 56 has a third extension.
NO limited by the control speed unit 52 _XSmell under the influx of
Of the oxygen generated during decomposition by the measurement pump cell 54.
Apply a voltage that gives a limit current to the pumping
I can do it.

On the other hand, of the lower surface of the second solid electrolyte layer 12f, on the entire lower surface forming the second chamber 20, a porous cermet electrode (for example, Au1%
And an auxiliary pump electrode 60 made of a Pt.ZrO ₂ cermet electrode containing
0, the second solid electrolyte layer 12f and the outer pump electrode 32 of the main pump cell 34 constitute an auxiliary electrochemical pump cell, that is, an auxiliary pump cell 62.

As with the inner pump electrode 30 in the main pump cell 34, the auxiliary pump electrode 60 is made of a material that has reduced or no reduction ability for NO components in exhaust gas. In this case, for example, La
It is preferable to be composed of a compound having a perovskite structure such as ₃ CuO ₄ or a cermet of a metal having low catalytic activity such as Au and a ceramic, or a cermet of a metal having low catalytic activity such as Au and a Pt group metal and a ceramic. Further, when an alloy of Au and a Pt group metal is used as the electrode material, the amount of Au to be added is set to 0.03 to 0.03 to the entire metal component.
It is preferable to make it 35 vol%.

By applying a desired constant voltage Vp3 between the auxiliary pump electrode 60 and the outer pump electrode 32 in the auxiliary pump cell 62 through an external DC power supply 64, oxygen in the atmosphere in the second chamber 20 is reduced. It can be pumped to the outside space.

As a result, the oxygen partial pressure of the atmosphere in the second chamber 20 has a substantial effect on the measurement of the amount of the target component under the condition that NO in the exhaust gas cannot be reduced or decomposed substantially. Not low oxygen partial pressure values. In this case, the function of the second pump cell 34 in the first chamber 18 causes
Since the change in the amount of oxygen introduced into the chamber 20 is much smaller than the change in the gas to be measured, the oxygen partial pressure in the second chamber 20 is accurately and constantly controlled.

Therefore, the vehicle-mounted NO
_{In the X} sensor 10, the exhaust gas whose oxygen partial pressure is controlled in the second chamber 20 is led to the detection electrode 50.

Further, in the on-vehicle NO _X sensor 10,
As shown in FIG. 2, a heater 70 that generates heat by external power supply is embedded in a form sandwiched between the first and second substrate layers 12a and 12b from above and below.
The heater 70 is provided to enhance the conductivity of oxygen ions. On the upper and lower surfaces of the heater 70, in order to obtain electrical insulation from the first and second substrate layers 12a and 12b, An insulating layer 72 of alumina or the like is formed.

The heater 70 is disposed over the entirety of the first chamber 18 to the second chamber 20.
The first chamber 18 and the second chamber 20 are each heated to a predetermined temperature, and the main pump cell 34, the control oxygen partial pressure detection cell 40, and the measurement pump cell 54 are also heated and maintained at the predetermined temperature. ing.

Here, the operation of the in-vehicle NO _X sensor 10 will be described. First, the tip end side of the on-vehicle NO _X sensor 10 is disposed in the external space, whereby the exhaust gas flows into the first chamber 18 under a predetermined diffusion resistance through the space 22 and the first diffusion control part 26. be introduced. The exhaust gas introduced into the first chamber 18 is supplied to the outer pump electrode 32 and the inner pump electrode 30 constituting the main pump cell 34.
During this time, a pumping action of oxygen caused by application of a predetermined pump voltage Vp1 is applied, and the oxygen partial pressure is controlled to a predetermined value, for example, 10 ⁻⁷ atm. This control is performed through the feedback control system 42.

The first diffusion-controlling section 26 narrows down the amount of oxygen in the gas to be measured that diffuses into the measurement space (first chamber 18) when the pump voltage Vp1 is applied to the main pump cell 34. , And functions to suppress the current flowing through the main pump cell 34.

Further, in the first chamber 18, even under the heating environment by the external exhaust gas and further under the heating environment by the heater 70, the NO.
A state under an oxygen partial pressure where _X is not reduced, for example, NO → 1 /
A situation has been formed under an oxygen partial pressure where the reaction of 2N ₂ + 1 / 2O ₂ does not occur. This is because if NO in the exhaust gas is reduced in the first chamber 18, accurate measurement of NO in the second chamber 20 at the subsequent stage cannot be performed. In the above, it is necessary to form a situation in which NO cannot be reduced by the components involved in the reduction of NO (here, the metal component of the inner pump electrode 30). Specifically, as described above, NO pump is applied to the inner pump electrode 30.
This is achieved by using a material having low reducibility, for example, an alloy of Au and Pt.

Although the measurement accuracy of NO may decrease, NO may be decomposed in the main pump cell 34 to some extent.

The gas in the first chamber 18 is
The second diffusion resistance is controlled by the diffusion control unit 28 under a predetermined diffusion resistance.
It is introduced into the chamber 20. The gas introduced into the second chamber 20 is supplied to the auxiliary pump electrode 60 constituting the auxiliary pump cell 62.
And a pumping action of oxygen caused by the application of the voltage Vp3 between the reference electrode 38, and the oxygen partial pressure is finely adjusted so as to have a constant low oxygen partial pressure value.

The second diffusion-controlling section 28 supplies a voltage V to the auxiliary pump cell 62 similarly to the first diffusion-controlling section 26.
When p3 is applied, the amount of oxygen in the gas to be measured diffused and flows into the measurement space (the second chamber 20) is reduced, and the pump current Ip3 flowing through the auxiliary pump cell 62 is suppressed.

The gas to be measured whose oxygen partial pressure has been controlled in the second chamber 20 as described above is passed through the third diffusion-controlling section 52 to the detection electrode 5 under a predetermined diffusion resistance.
It will be led to 0.

[0051] When an attempt is made to control the main pump cell 34 by operating the first chamber 18 the partial pressure of oxygen in the atmosphere to substantially affect no low value of the partial pressure of oxygen in the NO _X measurements, in other words, the control When the pump voltage Vp1 of the variable power supply 36 is adjusted through the feedback control system 42 so that the voltage V1 detected by the oxygen partial pressure detection cell 40 for use becomes constant, the oxygen concentration in the gas to be measured is large, for example, 0 ~ 20
%, The oxygen partial pressures of the atmosphere in the second chamber 20 and the atmosphere near the detection electrode 50 usually slightly change. This is because, when the oxygen concentration in the gas to be measured increases, an oxygen concentration distribution occurs in the width direction and the thickness direction of the first chamber 18, and this oxygen concentration distribution changes according to the oxygen concentration in the gas to be measured. Conceivable.

[0052] However, in this vehicle NO _X sensor 10, to the second chamber 20, the partial pressure of oxygen in its internal atmosphere always has a low oxygen partial pressure value constant, an auxiliary pumping cell 62 The first room 18
Even if the oxygen partial pressure of the atmosphere introduced into the second chamber 20 changes according to the oxygen concentration of the gas to be measured, the pumping operation of the auxiliary pump cell 62 reduces the oxygen partial pressure of the atmosphere in the second chamber 20. can be always made to have a constant low value, as a result, it is possible to control the low value of the partial pressure of oxygen which does not substantially affect the measurement of the nO _X.

Then, the NO _X of the gas to be measured introduced into the detection electrode 50 is reduced or decomposed around the detection electrode 50 to cause, for example, a reaction of NO → 1 / 2N ₂ + 1 / 2O ₂ . At this time, the measurement pump cell 5
4, between the detection electrode 50 and the reference electrode 38.
A predetermined voltage Vp2 is applied in a direction in which oxygen is pumped from the second chamber 20 to the reference gas introduction space 16 side.

[0054] Therefore, the pumping current Ip2 flowing through the measuring pumping cell 54, the oxygen concentration in the atmosphere introduced into the second chamber 20, i.e., NO _X by the detection electrode 50 and the oxygen concentration in the second chamber 20 is reduced or It is a value proportional to the sum of the concentration of oxygen generated by decomposition.

[0055] In this case, the oxygen concentration in the atmosphere in the second chamber 20, since it is controlled to be constant by means of the auxiliary pumping cell 62, the pumping current Ip2 flowing through the measuring pumping cell 54, the concentration of the NO _X It will be proportional. The concentration of the NO _X, since it corresponds to the diffusion amount of the NO _X which is limited by the third diffusion control part 52, even when the oxygen concentration in the measurement gas greatly changes, the measuring pumping cell It becomes possible to accurately measure the NO _X concentration from 54 through the ammeter 58.

[0056] From this, the value of the pump current Ip2 in the measuring pumping cell 54 is mostly represents the amount of NO _X is reduced or decomposed, therefore, also not as dependent on the oxygen concentration in the measurement gas .

In-vehicle NO _X sensor 1 operating in this manner
0 denotes an ECU 1 that controls the amount of fuel supplied to a fuel chamber (not shown) of the automobile engine 100, as shown in FIG.
20 is electrically connected. More specifically, the on-vehicle NO _X sensor 10 includes a NO _X detecting unit 122 and a sensor driving unit 124, of which the sensor driving unit 124
26, it is electrically connected to the ECU driving unit 128 of the ECU 120. That is, the sensor drive unit 124 and the ECU drive unit 128 can exchange signals with each other via the bus 126. Of course, the output voltage of the on-vehicle NO _X sensor 10 for various NO _X concentrations is measured in advance before being installed in the gas exhaust system 102, and is calibrated without any offset.

When measuring the NO _X concentration using such an in-vehicle NO _X sensor 10, first, while the vehicle engine 100 is driven, it is placed near the NO _X detection unit 122 using the in-vehicle battery as a power source. The heated heater (not shown) is energized. By this energization, the NO _X detection unit 12
2, NO _X concentration measurable temperature, specifically 800
The temperature is raised to about ° C.

During the operation of the vehicle engine 100, fuel and air are supplied to the combustion chamber of the vehicle engine 100.
Mixed. A spark plug is mounted in the combustion chamber, and sparks scatter from the spark plug toward the combustion chamber. Fuel is ignited by this spark, and as a result, the combustion chamber becomes hot, and the ignited fuel is combined with oxygen in the air and burned.

[0060] When the fuel is burned is compounded some oxygen and nitrogen in the air to a high temperature, thereby NO _X is produced. When this NO _X reaches the NO _X detecting unit 122 of the NO _X sensor 10 for vehicle installation, the NO _X for vehicle
The output voltage Va of the sensor 10 (the detection electrode 50 and the reference electrode 3
8 in which the pump current Ip2 that is converted into a voltage is changed. For example, when the constituent material of the NO _X detection unit 122 is ZrO ₂ , the output voltage Va increases as the NO _X concentration increases.

The output voltage Va of the on-vehicle NO _X sensor 10
As a signal from the sensor driver 124 of the vehicle NO _X sensor 10 via the bus 126 and ECU driver 128 is sent to the ECU 120. The ECU 120 includes:
If it is recognized that the output voltage Va has changed, NO
Judge that the _X concentration has changed. Further, the ECU 1
When the NO 20 detects that the NO _X concentration has exceeded a predetermined threshold value, the control unit 20 controls the fuel supply amount to the combustion chamber of the automobile engine 100 to be reduced.

If the measurement of the NO _X concentration is repeatedly performed over a long period of time, the measured NO _X concentration of the NO _X sensor 10 will be offset. That is, the actual N
Even O _X concentration 0, vehicle NO _X sensor 10 -5
It exhibits a measured concentration of NO _X ～5Ppm. Therefore, the actual NO _X concentration and the measured NO _X in the low concentration region
To match the density value, vehicle NO _X sensor 10
Needs to be re-calibrated.

Next, with reference to a flowchart shown in FIG. 5, a description will be given offset recalibration method of vehicle NO _X sensor according to the present embodiment. As shown in FIG. 5, in this offset recalibration method, the supply of fuel to the combustion chamber of the vehicle engine 100 is stopped while the vehicle engine 100 is operating, so that the gas exhaust system 1
02 is 0.5% or more when the oxygen concentration is 20% or more.
The recalibration of the offset of the in-vehicle NO _X sensor 10 is performed when the time is maintained for not less than second, preferably not less than 1 second, more preferably not less than 2 seconds. As described above, the oxygen concentration is derived from the output voltage Vb obtained by converting the pump current Ip1 flowing between the outer pump electrode 32 and the inner pump electrode 30 into a voltage, and the value of the output voltage Vb is always calculated by the ECU 120.
Sent to

For example, while the vehicle is running at high speed, the driver
If a sudden stop is performed by rake operation, the vehicle engine
The fuel supply to the 100 combustion chambers is stopped. in this case,
Although only air is supplied to the combustion chamber,
Combustion does not occur, and the combustion chamber becomes hot.
Oxygen and nitrogen in the air must combine with each other
It is discharged without. That is, the gas discharge system 102 is empty.
Gas is discharged, the acid in the gas discharge system 102 is discharged.
Element concentration rises rapidly and eventually reaches 20% or more (S
1). NO_XIs not generated, so NO_XSen
NO in the gas exhaust system 102 in which the_X
The density becomes 0. That is, NO for vehicle_XSensor 10
This is the best atmosphere for re-calibrating the offset. Ma
NO for in-vehicle use _XThe output voltage Va of the sensor 10 becomes the lowest.
You.

When the oxygen concentration in the gas discharge system 102 is 2
When it becomes 0% or more, the built-in timer of the sensor drive unit 124 starts time measurement (S2), and measures the duration of the state where the oxygen concentration is 20% or more (S3). And
When the duration reaches 0.5 seconds, preferably 1 second, and more preferably 2 seconds, the sensor driver 124 performs re-calibration of the offset.

On the other hand, as described above, the automobile engine 10
When the fuel supply 0 into the combustion chamber is stopped, vehicle NO _X
The sensor driving unit 124 of the sensor 10 can also receive a “fuel supply stop” signal issued by the ECU 120 via the bus 126 as shown in parentheses in FIG.
That is, in this embodiment, after the sensor driver 124 of vehicle NO _X sensor 10 receives a signal of "fuel supply stop", it is more preferable to perform the re-calibration of the offset of the vehicle NO _X sensor 10 .

In-vehicle NO _X receiving the above two signals
Sensor driver 124 of the sensor 10, vehicle N by reconstructing the information of the NO _X concentration sent to ECU120
Recalibration offset O _X sensor 10 (S4).
That is, a signal is sent to the ECU 120 indicating that the output voltage Va of the on-vehicle NO _X sensor 10 at this time is the output voltage when the NO _X concentration is 0. As a result, the actual NO _X concentration matches the measured NO _X concentration value obtained by the vehicle-mounted NO _X sensor 10.

When the state where the oxygen concentration is 20% or more is less than 0.5 second, that is, when the fuel supply into the combustion chamber of the automobile engine 100 is restarted before reaching 0.5 second, the output voltage Va of the vehicle NO _X sensor 10
May rise without showing a minimum. If the offset is re-calibrated in such a case, the actual NO _X concentration value does not match the measured NO _X concentration value. In addition, the offset may be larger. Therefore, re-calibration is not performed (S5).

When the offset of the on-vehicle NO _X sensor 10 is re-calibrated in this manner, the vehicle engine 100
Is being driven, the vehicle-mounted battery is constantly charged. Therefore, never be excessively discharged該車mounting battery be energized vehicle NO _X sensor 10 in order to raise the temperature of the NO _X detection unit 122. That is, the performance of the vehicle-mounted battery does not deteriorate early.

Since the gas discharge system 102 is energized, unburned fuel is quickly discharged to the outside.
Therefore, there is no fear of igniting the fuel remaining in the gas discharge system 102.

[0071] In the embodiments described above, the NO _X sensor 10 for mounting was measured oxygen concentration in the gas exhaust line 102, an oxygen sensor as shown in FIG. 61
The oxygen sensor 50 may be installed separately and measured by the oxygen sensor 150.

In this embodiment, the vehicle-mounted NO_X
NO as sensor 10_XThe output voltage increases as the concentration increases
Recalibration of offset was performed by exemplifying the rising one
But NO _XThe output voltage decreases as the concentration increases
Can be recalibrated in the same way for
You. In this case, the offset value becomes the maximum output voltage value.
You can do it.

[0073]

As described in the foregoing, according to the offset recalibration method of vehicle NO _X sensor according to the present invention, vehicle under the circumstance where the concentration of the NO _X discharged from the automobile engine during driving becomes 0 to recalibrate the offset of use NO _X sensor. Therefore, since the current in-vehicle NO _X sensor in a state where the vehicle battery is constantly charged, it is not to excessively discharged該車mounting battery. That is, the performance of the vehicle-mounted battery does not deteriorate early. Further, since the gas discharge system is energized, unburned fuel is quickly discharged to the outside. Therefore, there is no fear of igniting unburned fuel remaining in the gas discharge system.

N discharged from the driving automobile engine
A situation where the concentration of O _X is 0, i.e., when the fuel supply to the combustion chamber of an automotive engine is stopped, NO _X sensor onboard the signal of the engine electronic control unit has issued "fuel supply stop" It is preferable that the offset be re-calibrated after that. Accordingly, for example, when the oxygen concentration increases while NO _X is being discharged due to poor combustion of the fuel, the offset of the NO _X sensor for the vehicle is not re-calibrated.
_{The X} sensor offset can be reliably re-calibrated.

[Brief description of the drawings]

FIG. 1 is an overall schematic plan view showing an installation position of a vehicle-mounted NO _X sensor in a gas discharge system.

FIG. 2 is a schematic plan view showing the configuration of a vehicle-mounted NO _X sensor.

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a schematic pattern explanatory view showing an electrical connection pattern between a vehicle-mounted NO _X sensor and an engine control unit.

FIG. 5 is a flowchart of the offset recalibration method for the vehicle-mounted NO _X sensor according to the present embodiment.

6 is a schematic pattern diagram illustrating the electrical connection pattern of the vehicle NO _X and oxygen sensors and the engine control unit.

[Explanation of symbols]

10 ... Automotive NO _X sensor 100 ...
Automobile engine 102 Gas emission system 120
ECU 122 ... NO _X detection unit 124 ...
Sensor driver Va, Vb ... output voltage

Claims (3)

[Claims] An in-vehicle NO _X for re-calibrating an offset between a measured NO _X concentration and an actual NO _X concentration generated in an in-vehicle NO _X sensor installed in a gas exhaust system of an automobile engine while the automobile engine is operating. An offset recalibration method for a sensor, wherein a state in which oxygen concentration in exhaust gas in a gas exhaust system is 20% or more is maintained for a predetermined time by stopping fuel supply to a combustion chamber of the vehicle engine. To
Offset recalibration method of vehicle NO _X sensor, characterized in that the measuring NO _X concentration value of vehicle NO _X sensor zero. 2. A offset recalibration method of claim 1, wherein the offset recalibration method of vehicle NO _X sensor, wherein the predetermined time is not less than 0.5 seconds. 3. An apparatus according to claim 1 or 2 offset recalibration method described, the re-calibration of vehicle NO _X-sensor offset, the engine electronic control unit when the fuel supply to the combustion chamber of an automotive engine is stopped A re-calibration method for the on-vehicle NO _X sensor, which is performed after the on-vehicle NO _X sensor receives the signal of “fuel supply stop” issued by the vehicle.