JP3265635B2 - Oxygen concentration measuring device in internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring oxygen concentration in an internal combustion engine, and more particularly, to a process for calibrating an output signal value of an oxygen concentration sensor used for controlling an air-fuel ratio of an internal combustion engine to determine the oxygen concentration in exhaust gas. It relates to a device for accurately measuring.

[0002]

2. Description of the Related Art Various types of air-fuel ratio control devices for internal combustion engines have been proposed. The air-fuel ratio control device measures the residual oxygen concentration in the exhaust gas using an oxygen concentration sensor installed in the exhaust pipe, and based on the measured value, adjusts the air-fuel mixture on the intake side to an ideal air-fuel ratio, for example. This controls the fuel injection amount.
In such oxygen concentration measurement, for example, a zirconia oxygen sensor is used. A zirconia oxygen sensor may generate an output proportional to the oxygen concentration when the temperature of the sensor reaches an active region. Since the oxygen sensor is exposed to high-temperature exhaust gas in the exhaust pipe, the characteristics of the sensor change due to the exhaust gas component adhering to the sensor detector or the sensor detector gradually deteriorating over time, resulting in a change in the sensor characteristics. Gradually increases or decreases. Therefore, it is necessary to calibrate the output value of the oxygen sensor to determine the actual oxygen concentration.

In connection with the above-mentioned calibration processing, Japanese Patent Application Laid-Open No. 58-5 / 1983
No. 7050 discloses that during fuel cut when the exhaust pipe becomes atmospheric oxygen concentration during engine operation, that is, when the vehicle is running and is decelerating at or above a predetermined engine speed (for example, during engine braking), or the starter is driven. An apparatus that measures the oxygen concentration in the exhaust pipe before starting the engine that is not performed, obtains an output value of the current oxygen concentration sensor with respect to the atmospheric oxygen concentration state, and calculates a calibration value necessary for the calibration process from this output value is disclosed. I have.

[0004]

However, in obtaining the calibration value as described above, the oxygen concentration sensor in the exhaust pipe continues to be greatly cooled by the exhaust flow having a low exhaust temperature when the fuel is cut during the operation of the engine. It is difficult to heat the active area. That is, it is extremely difficult to obtain sufficient time for heating. Further, in an automatic vehicle, the fuel cut is not performed, or even if the fuel cut is performed for a short period, exhaust gas is always present in the exhaust pipe, and the exhaust pipe cannot be brought into the atmospheric oxygen concentration state. Therefore, there is no opportunity to obtain a calibration value unless the engine is started.

Accordingly, an object of the present invention is to obtain a calibration value of the output of the oxygen concentration sensor without being affected by the exhaust flow during the operation of the engine, and to obtain the calibration value during the operation of the engine even in an automatic vehicle. It is an object of the present invention to provide an oxygen concentration measuring device which can accurately determine an actual oxygen concentration using the calibration value.

[0006]

FIG. 1 shows an embodiment of an apparatus configuration according to the present invention. An apparatus for solving the above-mentioned problem is an oxygen concentration measuring apparatus that obtains an oxygen concentration in exhaust gas passing through an exhaust passage 1 of an internal combustion engine from an output signal of an oxygen concentration sensor 2 provided in the exhaust passage. Density sensor 2
Measurement area 3 which contains and is temporarily isolated from exhaust gas
And a bypass exhaust passage 5 through which the exhaust gas passes when the measurement region 3 is formed.
When the measurement region 3 is formed, the atmosphere supply means 6 supplies the atmosphere to the measurement region to set the inside of the measurement region to the atmospheric oxygen concentration state, and the measurement is performed when the measurement region 3 is in the atmospheric oxygen concentration state. Calibration value calculation means 7 for calculating a calibration value from the output value of the oxygen concentration sensor, storage means 8 for storing the above calibration value, and this calibration value for measuring the oxygen concentration in the exhaust gas in the exhaust passage 1. Calibrating means 9 for determining the oxygen concentration by calibrating the output value of the oxygen concentration sensor by using the calibration means.

[0007]

According to the above arrangement, during the operation of the internal combustion engine, the measurement region forming means 4 temporarily forms the measurement regions 3 in the exhaust passage 1 at desired time intervals. The exhaust gas flows through the bypass exhaust passage 5 while the measurement region is being formed. As a result, the oxygen concentration sensor 2 in the measurement area 3 is isolated from the exhaust gas, and is not cooled by the exhaust flow even when the fuel is cut. At the same time as the measurement area 3 is formed, the atmosphere is supplied into the measurement area 3 by the air supply means 6 with a minute airflow, and after a predetermined time, the inside of the measurement area has the same oxygen concentration state as the atmosphere. At the same time, the oxygen concentration sensor 2 is heated for measurement, but since the sensor is in the measurement area and is cooled only by a small air flow,
The power consumption required for heating is reduced, and the battery voltage does not decrease due to the heating operation because the internal combustion engine is operating. When the measurement conditions are prepared in this way, the output value of the oxygen concentration sensor 2 with respect to the atmospheric oxygen concentration is measured and stored by the calibration value calculation means 7. The calibrating means 7 stores an output value initially set to be output from the oxygen concentration sensor 2 at the atmospheric oxygen concentration, and the two are compared, and for example, the ratio of the difference is calculated as a calibration value α. Is stored. When the calibration value is calculated, the temporarily formed measurement area 3 is switched to the original exhaust passage 1. Thereafter, the oxygen concentration sensor 2 is exposed to the exhaust gas in the exhaust passage 1, and outputs an output value corresponding to the oxygen concentration in the exhaust gas. The calibration means 8 multiplies the oxygen concentration output value by the calibration value, for example. And a calibrated oxygen concentration is determined. The oxygen concentration value determined in this way becomes an oxygen concentration value in which the deviation of the output characteristic due to the temporal change of the oxygen concentration sensor is compensated by the calibration processing.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows an embodiment in which the present invention is applied to a diesel engine 10 mounted on a vehicle. The engine 10 is provided with an exhaust gas recirculation control system (hereinafter, EGR system) related to air-fuel ratio control.

The diesel engine body 10 includes an intake pipe 1
2 and the exhaust pipe 14 are connected. Engine body 1
A piston 18 is arranged so as to be able to reciprocate in the zero cylinder block 16, and a cylinder head 20 is fixed on the cylinder block 16. A combustion chamber 22 is formed between the piston 18 and the cylinder head 20. Air is supplied to the combustion chamber 22 from the intake pipe 12 through the intake valve 24, and fuel is supplied from the injection nozzle 26 to form an air-fuel mixture. Is done. This mixture is used as the combustion chamber 2
After combustion in the exhaust gas 2, the exhaust gas passes through the exhaust valve 28 and exhaust gas 1
It is discharged to 4.

The engine 10 is provided with the EGR system as described above, and the EGR pipe 30 is connected from the exhaust pipe 14 to the intake pipe 12. An electromagnetic EGR valve 32 is provided in the EGR pipe 30. Such EG
In the R system, the amount of gas recirculating from the exhaust side to the intake side of the engine is adjusted by adjusting the opening of the EGR valve 32. An electronic control unit (ECU) 40 controls the EGR valve 32, is connected to a battery 44 via a relay switch 42, and is energized when the relay switch 42 is turned on. Electronic control unit 40
Are connected to an ignition switch 46 for emitting a signal by an ignition operation, a rotation angle sensor 48 for detecting the number of revolutions of the engine, an accelerator opening sensor 50 for detecting the accelerator opening, and the like.

The exhaust gas discharged to the exhaust pipe 14 flows through the exhaust passage 60 toward the muffler 62. In the exhaust passage, a plurality of valves 64 to 67 are formed as shown in the drawing. . Each of the valves 64 to 67 is normally in a state shown by a dotted line, and flows through the exhaust pipe 68. An oxygen sensor 70 provided in the exhaust pipe 68 measures the oxygen concentration of the exhaust gas, and the output value output from the oxygen sensor is set to EC via a signal line 52.
Sent to U40.

For example, as shown in FIG. 3, the oxygen concentration sensor 70 includes a cup-shaped oxygen ion conductive solid electrolyte 71 made of zirconia and a porous ceramic 72 covering the outer peripheral surface thereof. Is in contact with the exhaust gas in the exhaust pipe, and the oxygen ion conductive solid electrolyte 7
1 is in contact with the atmosphere. The inner peripheral surface and the outer peripheral surface of the solid electrolyte 71 are coated with a platinum thin film for anode and a platinum thin film for cathode, respectively, and a voltage is applied from the ECU 40 between the anode lead 73 and the cathode lead 74 connected to each platinum thin film. I have.

When the oxygen molecules in the exhaust gas come into contact with the porous ceramic 72, they diffuse into the porous ceramic and reach the platinum thin film for the cathode of the solid electrolyte 71. Here, the oxygen molecules to which electrons have been imparted contact the platinum thin film for anode after passing through the solid electrolyte, and emit electrons. As a result, a current is generated, and this current value becomes an output value proportional to the oxygen concentration. In order to obtain an output value from the oxygen concentration sensor 70, it is necessary to activate the sensor by heating the solid electrolyte 71 to, for example, about 650 ° C. or higher, and an electric heater 75 is provided in the solid electrolyte 71. . Further, a thermocouple 76 for measuring the temperature of the solid electrolyte is provided to heat the solid electrolyte 71 to a predetermined temperature. The heater 75 and the thermocouple 76 are controlled by the ECU 40, and the thermocouple 7
Heating power is supplied to the heater 75 in accordance with the temperature value measured in 6.

Normally, after inputting the output value of the oxygen concentration sensor, the ECU 40 performs a calibration process on the output value to calculate the oxygen concentration in the exhaust gas, and performs EGR control according to the calculated oxygen concentration. The oxygen concentration is calculated by performing a calibration process as described below.

Referring to FIG. 2 again, during the operation of the engine, the oxygen concentration sensor 70 measures the oxygen concentration of the exhaust gas in the exhaust passage 68 and outputs an oxygen concentration output value for EGR control. Is configured to temporarily measure the atmospheric oxygen concentration at predetermined time intervals and obtain a calibration value for calibrating the output value. This is because the characteristics of the oxygen concentration sensor, which may have changed from the initial characteristics due to the influence of the exhaust gas or the like, are calibrated to the initial characteristics to obtain an accurate oxygen concentration. This time interval can be set, for example, by the engine operating time, the running distance, or the integrated value of the engine speed.

The electronic control unit 40 temporarily sends a measurement area forming signal to each of the valves 64 to 67 at a predetermined time during the operation of the engine to bring each of the valves 64 to 67 into a solid line state. Thus, a measurement region 80 including the oxygen concentration sensor 70 is formed in the exhaust passage 68. As a result, the exhaust passage 68
The exhaust gas flowing through the exhaust gas flows through the exhaust passage 81.

In this embodiment, an air pump 82 is provided in the measurement area 80 on the upstream side of the oxygen concentration sensor 70, and the air with a predetermined minute air volume is supplied through a valve 65, and the air is supplied through the other valve 66. It is discharged to the discharge pipe 83. The measurement area 80 gradually approaches the atmospheric oxygen concentration by the air pump 82. When the atmospheric oxygen concentration is reached after a certain period of time, the output value of the oxygen concentration sensor 70 is taken into the ECU 40, and a calibration value is calculated from the output value and stored in the backup memory 41 in the ECU 40. After the calibration value is stored, the ECU 40 sends a return signal to each of the valves 64 to 67, and each of the valves returns to the state indicated by the dotted line. As a result, the exhaust gas flows into the exhaust passage 68, the oxygen concentration sensor 70 measures the oxygen concentration of the exhaust gas again, and the ECU 40 performs a calibration process on the output value from the oxygen concentration Calculate the concentration and execute EGR control.

FIG. 4 shows a map stored in the backup memory 41. This map shows the output characteristics of the oxygen concentration sensor 70 with the horizontal axis representing the oxygen concentration and the vertical axis representing the current output value IL of the oxygen concentration sensor. A solid characteristic line L indicates an initial output characteristic of the oxygen concentration sensor, and ILs
Is the value at the atmospheric oxygen concentration (output value at the atmospheric oxygen concentration of about 21%). On the other hand, the dotted characteristic line shows an example of the output characteristic of the oxygen concentration sensor whose output value has increased due to a change with time. For example, the current output value ILb is an output value when the atmospheric oxygen concentration is temporarily measured at a predetermined time interval as described above, and represents a recent output value obtained by measuring the atmospheric oxygen concentration with the oxygen concentration sensor. .

The calibration value in the calibration process is, for example, a ratio (α = ILs / IL) between the output value ILs and the output value ILb.
b) is used. In this case, when the output value IL from the oxygen concentration sensor is input, the ECU 40 first calculates a calibrated output value IL ′ by multiplying the value IL by the calibration value α. Next, using the above map, the oxygen concentration is obtained from this value IL ′, and the current EGR amount (actual EGR amount) is estimated. At the same time, the ECU 40 determines the target EGR amount from information such as the engine speed and the accelerator opening, and then calculates the difference between the target EGR amount and the actual EGR amount, and performs PI control on the actual EGR amount.
The opening of the EGR valve is controlled so that the amount matches the target EGR amount.

As described above, according to the present embodiment, the calibration value α of the oxygen concentration sensor is calculated and updated and stored at predetermined time intervals during the operation of the engine normally under the EGR control. The EGR control is performed based on the oxygen concentration measured using the calibration value α.

FIG. 5 shows an application example in which the embodiment of FIG. 2 is combined with an exhaust particulate post-treatment device (hereinafter referred to as a DPT system). Parts corresponding to those of the above embodiment are denoted by the same reference numerals.

The DPT system 86 uses a filter 89 inside a clam shell 88 provided in an exhaust passage 87 to collect exhaust particulates (particulates) in exhaust gas.
After the black smoke component in the exhaust gas is removed, the exhaust gas is released to the outside via the silencer 62. Then, after collecting a certain amount of exhaust particulates, the collected exhaust particulates are burned by the ignition means 90 to recover (hereinafter, regenerate) the collecting function of the filter 89. In the filter regeneration state, the electronic control unit 40 switches the state of the valves 91 to 94 to isolate the filter 89 from the exhaust gas, and at the same time, uses the air pump 82 to reduce the minute air flow in the direction opposite to the direction in which the normal exhaust gas flows. Let the air flow. During this time, the exhaust gas from the engine 10 and the exhaust gas of the exhaust particulate burned in the filter 89 pass through the exhaust pipe 9 through valves 91 and 92.
It is discharged to 5,96.

As shown, the oxygen concentration sensor 70 is disposed between the air pump 82 and the filter 89, and normally detects the oxygen concentration in the exhaust gas and outputs an output value for EGR control to the electric control unit 40. Send out. In this embodiment, as in the embodiment of FIG. 2, the output value from the oxygen concentration sensor is calibrated by the calibration value α in the electric control unit 40 to determine the oxygen concentration. However, in the present embodiment, the calibration value is determined when the DPT system 86 is performing the filter regeneration operation, that is, when the air pump 82 and the filter 89 are operated.
It is calculated when the interval becomes the atmospheric oxygen concentration. For example, the filter regeneration operation is performed on the order of several minutes to several tens of minutes.

FIG. 6 is a flowchart showing one operation of the calibration process according to this embodiment. The following operation is executed at predetermined time intervals by interruption. First, at step 100, an output value I corresponding to the oxygen concentration in the exhaust gas from the oxygen concentration sensor is obtained.
L is taken in, and in step 200, the output value IL is
In the same manner as in the embodiment, the sensor output value IL ′ calibrated by multiplying by the latest calibration value α is calculated. In step 300, D
It is determined whether the PT system is in a state of collecting exhaust particulates or in a state of regeneration of the filter. This can be determined from a state signal from each valve or the like.

If the DPT system is in the trapping state, step 500 is executed and normal EGR control is continued. The oxygen concentration value used for this EGR control is determined in Step 20
The sensor output value IL ′ calculated at 0 is used. on the other hand,
If the DPT system is in the playback state, step 310 is executed to determine whether the calibration value has been updated during the current playback state, that is, the latest calibration value α is calculated, and the calibration value in the storage device is updated. It is determined whether or not the calibration value has been updated. If the calibration value α has been updated, step 500 is executed, and EGR control is executed using the latest calibration value α. If the calibration value α has not been updated, step 40
At 0, a calibration value calculation routine is executed.

FIG. 7 is a time chart of the calibration value calculation routine.
Indicates a port number. DPT system is t₁Filter again at
When in the raw state, the electronic control unit operates each valve.
To prevent the exhaust gas from flowing into the filter,
Air is supplied to the isolated area by an air pump. this
Exhaust gas is gradually removed around the oxygen concentration sensor
Time T₁To reach atmospheric oxygen concentration. In this embodiment
When the oxygen concentration sensor heater is energized, filter regeneration
Start t ₁Stop at the point of time T_TwoLater t_TwoAt
Is restarted. This is the area around the oxygen concentration sensor.
Since the area is isolated and does not receive a large cooling effect, the concentration measurement
It is not necessary to heat the sensor except for the fixed time.
is there. Of course, during this time, the sensor may be kept in the preheated state.
Absent. This predetermined time T_TwoIs the area around the oxygen sensor
Time T until atmospheric oxygen concentration is reached by apump
₁And the time until the sensor is activated by the heater
Interval T_ThreeCan be calculated from the correlation with In other words, oxygen
The concentration sensor is t_ThreeAt the time of activation, and oxygen concentration
The surrounding area of the degree sensor becomes the same oxygen concentration state as the atmosphere,
At this time, the output value of the oxygen concentration is sampled.
It is set in advance.

FIG. 8 shows a flowchart of the calibration value calculation routine. First, in step 401, the DPT
System after the start of the filter regeneration, whether or said time T ₂ has elapsed. When no elapsed time T ₂ are, then returns to continue the non-energized state of the heater at step 402. On the other hand, when the elapsed time T ₂ proceeds to step 403, the oxygen concentration sensor to determine whether an active state. For this determination, the temperature value of the thermocouple in the sensor described above is used. If the oxygen concentration sensor is not in the active state, the power supply to the heater is continued in step 404, and the process returns.

If the sensor is in the active state in step 403, the power supply to the heater is stopped in step 405, and the process proceeds to step 406. Here, after the filter regeneration starts,
It determines whether or not the predetermined time T ₁ is passed. Proceeds to step 407 when the predetermined time T ₁ is being passed, takes in the output value ILb from the oxygen concentration sensor. This output value ILb is a value when the DPT system is in the filter regeneration state and the atmospheric oxygen concentration state does not include the exhaust gas. Then, the process proceeds to step 408, where the oxygen concentration sensor initially outputs the output value ILs in the atmospheric oxygen concentration state.
Is divided by the output value ILb to obtain the calibration value α.
Is calculated. In step 409, the calculated calibration value α is updated and stored in the backup memory of the electric control unit, and the output calibration routine ends.

In the output calibration routine, for example, if the calculated calibration value α does not fall within a predetermined range, it is possible to determine that there is some abnormality or the like and to issue an alarm ( Not shown).

As described above, in this embodiment, the calibration value α is updated when the DPT system is in the filter regeneration state,
In the state of collecting fine particles, the EGR control is performed with an accurate oxygen concentration determined using the latest calibration value α.

The present invention is not limited to the above embodiment as long as the oxygen concentration can be temporarily measured in the atmospheric oxygen concentration region during engine operation by appropriately configuring the exhaust pipe and each valve. It will be readily understood that any configuration may be applied to gasoline engines as well as diesel engines.

[0032]

As described above, according to the present invention, since the calibration value relating to the output calibration of the oxygen concentration sensor can be obtained while the engine is operating, for example, a long measurement time required for obtaining the calibration value before starting the engine is obtained. , And a reduction in battery power when the engine is started. Also, when calculating the calibration value during the operation of the engine, the area around the oxygen concentration sensor is temporarily isolated from the exhaust gas, so that the sensor is not greatly cooled by the exhaust gas flow. The calibration value is obtained without being affected by the residual exhaust gas. Further, the calibration value can be obtained at a desired time period that can be set in advance. As described above, since the calibration value is obtained under the optimum condition and is updated at predetermined time intervals, the output of the oxygen concentration sensor is always calibrated with the optimum calibration value, and an accurate oxygen concentration can be measured. Therefore,
Since the air-fuel ratio control can be executed based on the accurate oxygen concentration in the exhaust gas, it greatly contributes to the improvement of the power performance, exhaust gas purification and fuel efficiency of the internal combustion engine.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an oxygen concentration measuring device according to the present invention.

FIG. 2 is a configuration diagram showing one embodiment of an oxygen concentration measuring device according to the present invention.

FIG. 3 is a sectional view of an oxygen concentration sensor used in the embodiment of FIG.

FIG. 4 is a diagram showing a map stored in a backup memory in the embodiment of FIG. 2;

FIG. 5 is a configuration diagram showing an application example of the embodiment of FIG. 2;

6 is an operation flowchart of a sensor output value calibration process executed by the electric control unit of FIG.

FIG. 7 is a time chart of a calibration value calculation routine of FIG. 6;

8 shows a flowchart of a calibration value calculation routine of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Exhaust passage 2 ... Oxygen concentration sensor 3 ... Measurement area 4 ... Measurement area forming means 5 ... Bypass exhaust path 6 ... Atmospheric supply means 7 ... Calibration value calculation means 8 ... Storage means 9 ... Calibration means 12 ... Intake pipe 14 ... Exhaust Pipe 32 EGR valve 40 Electronic control unit (ECU) 64, 65, 66, 67 Valve 70 Oxygen concentration sensor 80 Measurement area 82 Air pump 86 Exhaust particulate after-treatment device (DPT system) 89 Filter 91 92, 93, 94 ... valve

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/26 361 F02D 35/00 368 F02D 45/00 368 G01N 27/409

Claims (1)

(57) [Claims] 1. An oxygen concentration measuring device for determining an oxygen concentration of exhaust gas passing through an exhaust passage (1) of an internal combustion engine from an output signal of an oxygen concentration sensor (2) provided in the passage. A measurement region forming means (4) for forming a measurement region (3) including a sensor and temporarily separating the oxygen concentration sensor from the exhaust gas; and a bypass exhaust passage for passing the exhaust gas when the measurement region is formed. (5) Atmosphere supply means (6) for supplying air to the measurement region when the measurement region is formed to bring the inside of the measurement region into an atmospheric oxygen concentration state; Calibration value calculation means (7) for calculating a calibration value from the output signal of the oxygen concentration sensor measured at the time of (2), storage means (8) for storing the calibration value, and exhaust gas passing through the exhaust passage (1). Oxygen in gas A calibration means (9) for determining an oxygen concentration by calibrating an output value from an oxygen concentration sensor using the calibration value when measuring the concentration.