JPH07117515B2 - Oxygen concentration detector for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oxygen concentration detection device for detecting the oxygen concentration in the exhaust gas of an internal combustion engine.

Background Art An air-fuel ratio that detects the oxygen concentration in the exhaust gas and purifies the air-fuel ratio of the air-fuel mixture supplied to the engine by feedback control to the target air-fuel ratio according to the detection results for the purpose of purifying exhaust gas from internal combustion engines and improving fuel efficiency. There is a fuel ratio control device. This air-fuel ratio control device uses an oxygen concentration sensor that is provided in the exhaust system of an internal combustion engine and that generates an output signal proportional to the oxygen concentration in the exhaust gas (see Japanese Patent Laid-Open No. 52-72286).

By the way, in this type of oxygen concentration sensor, in general, the output characteristics with respect to the air-fuel ratio fluctuate due to changes in the temperature of the sensor section, so-called exhaust gas temperature dependency, and further due to changes in the intake air amount Qa (changes in load), the sensor temperature It is known that there is so-called exhaust gas flow rate dependency. An error will occur in the sensor output due to these dependencies, and as a result, the detected air-fuel ratio will vary, and good air-fuel ratio control cannot be expected.

As a countermeasure against the exhaust temperature dependency and the exhaust flow rate dependency, first, for the exhaust temperature dependency, a heater is attached to the sensor body and the heater temperature is controlled according to the operating parameters of the engine to keep the element temperature constant. As for the method for maintaining the above, and for the dependence on the exhaust gas flow rate, a method is adopted in which a protective cover is attached to the sensor body and the protective cover is multiplexed to mitigate the direct influence of the exhaust gas flow rate.

However, the former requires a complicated control circuit for controlling the heater temperature, and the latter has a problem that the structure of the sensor main body becomes complicated due to the multiple structure of the protective cover.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned points, and depends on a change in exhaust temperature and a change in exhaust flow rate without complicated temperature control of a heater and without complicating the structure of a sensor body. An object of the present invention is to provide an oxygen concentration detection device for an internal combustion engine, which can obtain a detection output that does not exist.

The oxygen concentration detecting apparatus for an internal combustion engine of the present invention obtains a means for detecting an operating parameter indicating the engine speed and the engine load of the internal combustion engine, and obtains a correction coefficient based on the operating parameter indicating the engine speed and the engine load. A means for correcting the output signal of the oxygen concentration sensor based on the correction coefficient is provided.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

In FIGS. 1A and 1B, the oxygen concentration sensor main body 10
Is a substantially cubic oxygen ion conductive solid electrolyte member 1
This oxygen ion conductive solid electrolyte member 1 having
First and second gas retention chambers 2 and 3 are formed therein.
The first gas retention chamber 2 communicates with an introduction hole 4 for introducing the exhaust gas of the gas to be measured from the outside of the solid electrolyte member 1, and the introduction hole 4 is the first exhaust gas inside the exhaust pipe (not shown) of the internal combustion engine. It is located so that it can easily flow into the gas retention chamber 2.
A communication hole 5 is formed in a wall portion between the first gas retention chamber 3 and the second gas retention chamber 3, and exhaust gas is introduced into the second gas retention chamber 3 through the introduction hole 4, the first gas retention chamber 2, and It is designed to be introduced through the communication hole 5.

Further, the oxygen ion conductive solid electrolyte member 1 is formed with a gas reference chamber 6 for introducing outside air or the like so as to separate the walls from the first and second gas retention chambers 2 and 3. Electrode protection holes 7 are formed in the walls of the first and second gas retention chambers 2 and 3 opposite to the gas reference chamber 6. Electrode pairs 12a, 12b, 11a, 11b are formed on the wall between the first gas retention chamber 2 and the gas reference chamber 6 and on the wall between the first gas retention chamber 2 and the electrode protection hole 7, respectively. Also, electrode pairs 14a, 14b, 13a, 13b are provided on the wall between the second gas retention chamber 3 and the gas reference chamber 6 and on the wall between the second gas retention chamber 3 and the electrode protection hole 7, respectively. Has been formed. The solid electrolyte member 1 and the electrode pairs 11a and 11b are the first oxygen pump element 15
As a result, the solid electrolyte member 1 and the electrode pairs 12a and 12b act as the first battery element 16, respectively. The solid electrolyte member 1 and the electrode pair 13a, 13b act as the second oxygen pump element 17, and the solid electrolyte member 1 and the electrode pair 14a, 14b act as the second battery element 12, respectively.

Further, heater elements 19 and 20 are provided on the outer wall surface of the gas reference chamber 6 and the outer wall surface of the electrode protection hole 7, respectively. Heater element 19,
20 is electrically connected in parallel to each other, and includes first and second oxygen pump elements 15, 17 and first and second battery elements 16,
While heating 18 evenly, the heat retention in the solid electrolyte member 1 is improved. The oxygen ion conductive solid electrolyte member 1 is integrally formed from a plurality of pieces. Also the first
Also, it is not necessary to form the wall portion of the second gas retention chamber from all the oxygen ion conductive solid electrolyte, and at least only the portion where the electrode pair is provided may be formed of the solid electrolyte.

ZrO ₂ (zirconium dioxide) is used as the oxygen ion conductive solid electrolyte member 1, and Pt (platinum) is used as the electrodes 11a to 14b.

In FIG. 2, a current supply circuit 21 is connected to the first and second oxygen pump elements 15 and 17 and the first and second battery elements 16 and 18. As shown in FIG. 2, the current supply circuit 21 includes a differential amplifier circuit 22,23, a current detection resistor 24,25, a reference voltage source 26,2.
7 and switching circuits 28 and 29. The outer electrode 11a of the first oxygen pump element 15 is a switch 28a of the switching circuit 28 and a current detection resistor.
The inner electrode 11b is connected to the output terminal of the differential amplifier circuit 22 via 24, and is grounded via the switch 29a of the switching circuit 29. The outer electrode 12a of the first battery element 16 is connected to the inverting input terminal of the differential amplifier circuit 22, and the inner electrode 12b is grounded via the switch 29b of the switching circuit 29.

Similarly, the outer electrode 13a of the second oxygen pump element 17 is connected to the switching circuit 2
Differential amplifier circuit via switch 28b of 8 and current detection resistor 25
The inner electrode 13b is connected to the output terminal of 23 and is grounded via the switch 29a of the switching circuit 29. The outer electrode 14a of the second battery element 18 is connected to the inverting input terminal of the differential amplifier circuit 23, and the inner electrode 14b is connected to the switch 2 of the switching circuit 29.
It is designed to be grounded via 9b. A reference voltage source 26 is connected to the non-inverting input terminal of the differential amplifier circuit 22, and a reference voltage source 27 is connected to the non-inverting input terminal of the differential amplifier circuit 23. The output voltage of the reference voltage sources 26, 27 is a voltage (for example, 0.4 V) corresponding to the stoichiometric air-fuel ratio. Both ends of the current detection resistor 24 form an output of the first sensor, and both ends of the current detection resistor 25 form an output of the second sensor. Current detection resistor 2
The voltage between both ends of 4, 25 is supplied to the control circuit 30. Positive and negative power supply voltages are supplied to the differential amplifier circuits 22 and 23.

In order to detect a plurality of operating parameters of the internal combustion engine, for example, an intake pipe negative pressure (P _B ) sensor 31 and a TDC pulser 32 for outputting engine speed (Ne) information are provided. The P _B sensor 31 generates an output at a level according to the negative pressure P _B in the intake manifold (not shown), and the TDC pulser 32
Generates a pulse each time the piston reaches top dead center in conjunction with a crankshaft (not shown). The means for outputting the engine speed (Ne) information is one that generates a pulse each time the crankshaft rotates by a predetermined angle, and one that detects a pulse generated in the primary coil of an ignition coil (not shown). May be

The control circuit 30 converts a differential input A / D (analog / digital) converter 301 that converts the voltage across the current detection resistors 24 and 25 into a digital signal and the output signal of the P _B sensor 31 into a digital signal. The A / D converter 302, the waveform shaping circuit 303 that shapes the output signal of the TDC pulser 32, and the generation interval of the TDC pulse output from the waveform shaping circuit 303 are counted by the clock from the clock generation circuit 304. A counter 305 for measuring by means of a drive circuit 306, a drive circuit 306 for switching and driving the switching circuits 28, 29, and a drive circuit 307 for driving the solenoid valve 33 to open.
From a heater current supply circuit 308 that supplies a current to the heater elements 19 and 20, a CPU (central processing circuit) 309 that performs digital calculation and the like according to a program, and a ROM 310 and a RAM 311 in which various processing programs and data are written in advance. Has become.

In the control circuit 30, the TDC pulse output from the waveform shaping circuit 303 is also supplied to the interrupt terminal of the CPU 309, which enables a TDC interrupt when the oxygen concentration sensor output correction process described later is performed. The pump current values I _P (1) and I _P (2) flowing through the current detection resistors 24 and 25, which are oxygen concentration sensor outputs, are transferred to the CPU 309 via the A / D converter 301.
Read in.

The solenoid valve 34 is provided in an intake secondary air supply passage (not shown) communicating with the intake manifold downstream of the engine carburetor throttle valve. Further, a current is supplied from the heater current supply circuit 308 to the heater elements 19 and 20, whereby the heater element 1
9,20 generate heat and oxygen pump elements 15,17 and battery elements 16,18
Is heated to an appropriate temperature higher than the exhaust gas.

In this structure, the exhaust gas in the exhaust pipe is introduced into the introduction hole
Flows into the second gas retention chamber 2 and diffuses. Further, the exhaust gas in the first gas retention chamber 2 passes through the communication hole 5 to the second gas retention chamber 3
It flows in and diffuses.

In the switching circuits 28 and 29, as shown in FIG.
Connects the electrode 11a to the current detection resistor 24, the switch 28b opens the connection line of the electrode 13a, the switch 29a grounds the electrode 11b and opens the connection line of the electrode 13b, and the switch 29b grounds the electrode 12b. Then, when it is set to the selection position where the connection line of the electrode 14b is opened, the selection state of the first sensor is set.

In the selected state of the first sensor, first, when the air-fuel ratio of the engine-supplied air-fuel mixture is in the lean region, the output level of the differential amplifier circuit 22 becomes a positive level, and this positive-level voltage is the resistance.
24 and the first oxygen pump element 15 are supplied to the series circuit.
Therefore, the pump current flows between the electrodes 11a and 11b of the first oxygen pump element 15. This pump current flows from electrode 11a to electrode 11b.
The oxygen in the first gas retention chamber 2 flows toward the electrode 11
At b, it is ionized, moves inside the first oxygen pump element 15, is released as oxygen gas from the electrode 11a, and oxygen in the first gas retention chamber 2 is pumped out.

By pumping out oxygen in the first gas retention chamber 2, an oxygen concentration difference occurs between the exhaust gas in the first gas retention chamber 2 and the gas in the gas reference chamber 6. Due to this difference in oxygen concentration, a voltage Vs is generated between the electrodes 12a and 12b of the battery element 16. This voltage Vs is supplied to the inverting input terminal of the differential amplifier circuit 22. Differential amplifier circuit 22
Since the output voltage of is equal to the voltage difference between the voltage Vs and the output voltage Vr ₁ of the reference voltage source 26, the pump current value is proportional to the oxygen concentration in the exhaust gas.

When the air-fuel ratio is in the rich region, the voltage Vs exceeds the output voltage Vr ₁ of the reference voltage source 26. Therefore, the output level of the differential amplifier circuit 22 is inverted from the positive level to the negative level. Due to this negative level, the pump current flowing between the electrodes 11a and 11b of the first oxygen pump element 15 decreases and the current direction is reversed. That is, since the pump current flows from the electrode 11b to the electrode 11a, the external oxygen is ionized at the electrode 11a and moves in the first oxygen pump element 15 to move from the electrode 11b into the first gas retention chamber 2 as oxygen gas. It is released and oxygen is pumped into the first gas retention chamber 2. Accordingly, the pump current is pumped in and out by supplying the pump current so that the oxygen concentration in the first gas retention chamber 2 is always constant, so that the pump current value I _P and the output voltage of the differential amplifier circuit 22. Is proportional to the oxygen concentration in the exhaust gas in the lean and rich regions, respectively. A solid line a in FIG. 3 shows the pump current value I _P.

The pump current value I _P is the charge e, the diffusion coefficient of the introduction hole 4 to the exhaust gas is σ _O , and the oxygen concentration in the exhaust gas is P _O ex
When h is the oxygen concentration in the first gas retention chamber 2 and P _O v, it can be expressed by the following equation.

I _P = 4eσ _O (P _O exh-P _O v) (1) where the diffusion coefficient σ _O is the area of the introduction hole 4, A is the Boltzmann constant, k is the absolute temperature, and T is the length of the introduction hole 4. Let l be the length and D be the diffusion constant.

σ _O = D · A / kTl (2) Next, the switch 28a opens the connection line of the electrode 11a, the switch 28b connects the electrode 13a to the current detection resistor 25, and the switch 29a grounds the electrode 13b. And open the connection line of electrode 11b, and switch 29b grounds electrode 14b and
Once in the selected position to open the 12b connection line, the second
The sensor is selected.

In the selected state of the second sensor, the pump current is the electrode of the second oxygen pump element 12 so that the oxygen concentration in the second gas retention chamber 3 is always constant by the same operation as the selected state of the first sensor described above. Oxygen is supplied to between 13a and 13b, and oxygen is pumped in or pumped out. Therefore, the pump current value I _P and the output voltage of the differential amplifier circuit 23 are different from the oxygen concentration in the exhaust gas in the lean and rich regions, respectively. It is proportional. The pump current value I _{P in} the second sensor selected state is defined by the diffusion coefficient σ _O in the above formula (1) by the introduction hole 4 and the communication hole 5, and P _O v is the oxygen in the second gas retention chamber 3. It is represented by the concentration. The magnitude of the pump current value I _P is the fourth
As shown in the figure, it is clear that in the lean and rich regions of the air-fuel ratio, the larger the diffusion resistance inversely proportional to the magnitude of the diffusion coefficient σ _O , the smaller the diffusion resistance. Therefore, since the diffused resistance becomes larger in the second sensor selection state than in the first sensor selection state, the magnitude of the pump current value I _P becomes smaller in the lean and rich regions as shown by the broken line b in FIG. By adjusting the size and length of the communication hole 5, as shown in FIG. 3, the pump current direct value characteristic in the rich region in the second sensor selected state is changed to the pump current value in the lean region in the first sensor selected state. The characteristics are linearly continuous at I _P = 0. In addition, the differential amplifier circuit 22,
The output voltage characteristic of 23 also becomes linearly continuous at 0 [V].

The control circuit 30 also performs a process of correcting the output signal of the oxygen concentration sensor 10. In order to perform the correction processing of the sensor output, the ROM 310 in the control circuit 30 is shown in advance in FIG. 5 in association with a plurality of operating parameters of the internal combustion engine, for example, the engine speed Ne and the intake pipe negative pressure P _B. The correction coefficient thus set is stored as a Ne-P _B map.
Then, the CPU 309 performs the sensor output correction process according to the procedure shown in the flowchart of FIG. It should be noted that this correction process is performed by a TDC interrupt in a routine that is processed for each ignition in the engine control.

The CPU 309 first uses the TDC pulse from the waveform shaping circuit 303.
Interrupt processing is performed by the TDC interrupt (step 1). Then, the pump current values I _P (1) and I _P (2) flowing through the current detection resistors 24 and 25, which are the outputs of the oxygen concentration sensor 10, are read (step 2b), and then from the previous TDC timing to this time. The engine speed Ne is calculated based on the count number counted by the counter 305 by the TDC timing (step 3), and the intake pipe negative pressure sensor 37
The output voltage of is read (step 4). And
A correction coefficient corresponding to the detected engine speed Ne and the intake pipe negative pressure P _B is obtained from the Ne-P _B map of RO310, and the output of the oxygen concentration sensor 10 is corrected based on this correction coefficient (step 5). . As is clear from FIG. 5, the correction coefficient is large (for example, 1.2 times) when the engine speed Ne is low and the intake pipe negative pressure P _B is large, that is, when the intake air amount Qa is small. Number Ne is high and intake pipe negative pressure P
_{When B} is small, that is, when the intake air amount Qa is large, it is set to be small (for example, 0.8 times).

Sensor output correction processing is performed by the above series of procedures, which enables complicated temperature control of the heater elements 19 and 20, and multiple sensor cover mounting on the sensor body to complicate the structure of the sensor body. Even if it does not, it is possible to obtain the sensor output that does not depend on the exhaust temperature change and the exhaust flow rate change, only by changing the program of the ROM 310 and storing the Ne-P _B map in advance.

In the above embodiment, the case where the correction processing operation of the sensor output is performed by the control circuit 30 that performs the air-fuel ratio has been described, but a dedicated controller, memory, etc. for performing the correction processing are provided separately from the control circuit 30. Of course, it is okay to do so.

In the above embodiment, the correction coefficient is a Ne-P _B map.
Stored in ROM310 in advance and detected engine speed
The correction coefficient corresponding to Ne and the intake pipe negative pressure P _B is read out from the map of the ROM 310 and corrected, but a predetermined calculation is performed based on the engine speed Ne and the intake pipe negative pressure P _B detected by the CPU 309. It is also possible to obtain a correction coefficient by calculating with an equation and perform the correction based on this correction coefficient.

Furthermore, the oxygen concentration detection sensor used in the oxygen concentration detection device according to the present invention is not limited to the structure shown in FIGS. 1 (a) and 1 (b).

As described above, in the oxygen concentration detecting device according to the present invention, the operating parameter indicating the engine speed and the engine load amount of the internal combustion engine is detected, and the operating parameter indicating the engine speed and the engine load amount is detected. Since the correction coefficient based on this is obtained and the output signal of the oxygen concentration sensor is corrected based on this correction coefficient, it is possible to further complicate the structure of the sensor body without performing complicated temperature control of the heater. Therefore, it is possible to obtain a detection output that does not depend on changes in exhaust temperature and changes in exhaust flow rate. Therefore, variations in the detected air-fuel ratio due to the exhaust temperature dependency and the exhaust flow rate dependency can be prevented, and the accuracy of the air-fuel ratio control can be improved.

[Brief description of drawings]

FIG. 1 (a) is a plan view showing an embodiment of the oxygen concentration detection device according to the present invention, and FIG. 1 (b) is Ib-Ib of FIG. 1 (a).
A sectional view of a portion, FIG. 2 is a circuit diagram showing a current supply circuit including an air-fuel ratio control device, FIG. 3 is a diagram showing output characteristics of the device of FIG. 1, and FIG. 4 is a diffusion resistance and a pump current value. FIG. 5 is a characteristic diagram showing the relationship of FIG. 5, FIG. 5 is a diagram showing an example of the correction coefficient of the Ne-P _B map, and FIG. Explanation of symbols of main parts 1 …… Oxygen ion conductive solid electrolyte member 2,3 …… Gas retention chamber 4 …… Introduction hole 5 …… Communication hole 6 …… Gas reference chamber 10 …… Oxygen concentration sensor 15,17… … Oxygen pump element 16,18 …… Battery element 19,20 …… Heater element 21 …… Current supply circuit 30 …… Control circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Mieno 1-4-1 Chuo, Wako-shi, Saitama, Honda R & D Co., Ltd. (56) References JP-A-61-241654 (JP, A) JP Sho 62-179654 (JP, A)

Claims (2)

[Claims] 1. An oxygen concentration detecting device for an internal combustion engine, comprising an oxygen concentration sensor which is provided in an exhaust system of an internal combustion engine to detect an oxygen concentration in exhaust gas and to generate an output signal proportional to the oxygen concentration. A means for detecting an operating parameter indicating the engine speed and the engine load of the internal combustion engine; and a correction coefficient based on the operating parameter indicating the engine speed and the engine load, and the oxygen based on the correction coefficient. An oxygen concentration detecting device for an internal combustion engine, comprising: means for correcting an output signal of the concentration sensor. 2. The internal combustion engine according to claim 1, wherein the correction coefficient is stored in advance in a memory in correspondence with an operating parameter indicating the engine speed and the engine load amount. Oxygen concentration detector.