JPS62198747A - Oxygen concentration detecting device for internal combustion engine - Google Patents

Abstract

PURPOSE:To obtain a detection output which depends upon neither variation in exhaust temperature nor variation in exhaust air flow by detecting plural operation parameters of an internal combustion engine and correcting the output signal of an oxygen concentration sensor with a coefficient of correction based upon those operation parameters. CONSTITUTION:A suction pipe negative pressure sensor 31 and a TD pulser 34 for outputting engine rotating speed information are provided so as to detect plural operation parameters of the internal combustion engine. A CPU 309 corrects the output signal of the oxygen concentration sensor with the coefficient of correction based upon those operation parameters. The detection output which depends upon neither variation in exhaust temperature and variation in exhaust flow rate is therefore obtained without performing complicate temperature control by a heater current supply circuit 308 nor making the structure of the sensor body complex. Thus, variance in detected air-fuel ratio due to exhaust temperature dependency and exhaust flow rate dependency is eliminated, so the accuracy of air-fuel ratio control is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen concentration detection device for detecting the oxygen concentration in exhaust gas of an internal combustion engine.

For the purpose of exhaust gas purification and fuel efficiency improvement of internal combustion engines, the oxygen concentration in the exhaust gas is detected, and the air-fuel ratio of the air-fuel mixture supplied to the engine is fed back to the target air-fuel ratio according to the detection results. There is an air-fuel ratio control device that controls the air-fuel ratio.

This air-fuel ratio control device uses an oxygen concentration sensor that is installed in the exhaust system of an internal combustion engine and generates an output signal proportional to the oxygen concentration in the exhaust gas.
(See Publication No. 286, etc.).

By the way, this type of oxygen concentration sensor generally has a so-called exhaust temperature dependence, in which the output characteristic with respect to the air-fuel ratio varies depending on changes in the temperature of the sensor section, and furthermore, the output characteristic with respect to the air-fuel ratio varies depending on the temperature change of the sensor section.
It is known that there is a so-called exhaust flow rate dependence in which the sensor temperature fluctuates due to changes in the exhaust gas (changes in load).

These dependencies cause errors in the sensor output, resulting in variations in the detected air-fuel ratio, making it impossible to expect good air-fuel ratio control.

As a countermeasure against this exhaust temperature dependence and exhaust flow rate dependence, first, a heater is attached to the sensor body and the element temperature is kept constant by controlling the heater temperature according to the engine operating parameters. In order to reduce the dependence on the exhaust flow rate, methods have been adopted to reduce the direct influence of the exhaust flow rate by attaching a protective cover to the sensor body and layering these protective covers.

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

1. Further improvements and 1. The present invention has been made in view of the above-mentioned points, and is capable of controlling exhaust gas temperature changes and exhaust flow rate changes without complicated temperature control of the heater and without complicating the structure of the sensor body. An object of the present invention is to provide an oxygen concentration detection device for an internal combustion engine that can obtain a detection output that does not depend on the oxygen concentration.

The oxygen concentration detection device for an internal combustion engine according to the present invention detects a plurality of operating parameters of the internal combustion engine, obtains a correction coefficient based on these operating parameters, and corrects the output signal of the oxygen concentration sensor based on the correction coefficient. It is a feature.

Mi-Emperor-1 Embodiments of the present invention will be described below with reference to the drawings.

In FIGS. 1(a) and (b), the oxygen concentration sensor body 1
0 has a roughly cubic oxygen ion conductive solid electrolyte member 1, and inside this oxygen ion conductive solid electrolyte member 1, first and second gas retention chambers 2 and 3 are formed. . The first gas retention space 2 communicates with an introduction hole 4 through which exhaust gas of the gas to be measured is introduced from the outside of the solid electrolyte member 1. It is positioned so that it can easily flow into the gas retention chamber 2. A communication hole 5 is formed in the wall between the first gas retention space 2 and the second gas retention space 3, and the exhaust gas enters the second gas retention space 3 through the introduction hole 4 and the first gas retention chamber 2. , and is introduced through the communication hole 5.

Further, a gas reference chamber 6 into which outside air or the like is introduced is formed in the oxygen ion conductive solid electrolyte member 1 so as to be separated from the first and second gas reservoirs 2 and 3 by a wall.

Electrode protection holes 7 are formed in the walls of the first and second gas retention chambers 2.3 on the side opposite to the gas reference chamber 6. 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, an electrode pair 12a,
12b, 11a, and 11b are formed respectively, and electrode pairs are formed on the wall between the second gas retention chamber 3 and the gas reference chamber 6 and the wall between the second gas retention chamber 3 and the electrode protection hole 7. 14a, 1
4b, 13a, and 13b are formed, respectively. The solid electrolyte member 1 and the electrode pair 11a, 11b are the 11th! ! As the elementary pump element 15, the solid electrolyte member 1 and the electrode pair 12a
, 12b each act as the first battery element 16. Further, the solid electrolyte member 1 and the electrode pair 13a, 13b serve as the second oxygen pump element 17.
4a and 14b each act as a second N-cell element 18.

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. The heater elements 19, 20 are electrically connected to each other in parallel;
The first and second oxygen pump elements 15, 17 and the first and second battery elements 16, 18 are heated evenly, and the heat retention inside the solid electrolyte member 1 is improved. Note that the oxygen ion conductive solid electrolyte member 1 is integrally formed from a plurality of pieces. Further, it is not necessary that the walls of the first and second gas retention chambers are entirely made of an oxygen ion conductive solid electrolyte.
It is sufficient that at least only the portion where the electrode pair is provided is made of the solid electrolyte.

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

In FIG. 2, first and second W1 element pump elements 15.
17 and the first and second battery elements 16 and 18 are connected to a current supply circuit 21 . As shown in FIG. 2, the current supply circuit 21 includes differential amplifier circuits 22, 23, . Current detection resistors 24, 25. Reference voltage source 26.27 and switching circuit 28.
Consists of 29.

The outer M pole 11a of the first oxygen pump element 15 is connected to the switching circuit 2.
The switch 28a1 of No. 8 is connected to the output terminal of the differential amplifier circuit 22 via the current detection resistor 24, and the inner electrode 11b 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 output terminal of the differential amplifier circuit 23 via the switch 28b1 of the switching circuit 28, the current detection resistor 25, and the inner electrode 13b
is grounded via a switch 29a of the switching circuit 29.

The outer electrode 14a of the second battery element 18 is connected to the differential amplifier circuit 23.
The inner electrode 14b is connected to the inverting input terminal of the switching circuit 2.
It is configured to be grounded via one switch 29b. A reference voltage source 26 is connected to the non-inverting input terminal of the differential amplifier circuit 22, and a reference voltage +1127 is connected to the non-inverting input terminal of the differential amplifier circuit 23. Reference voltage source 26
．． The output voltage of 27 is a voltage corresponding to the stoichiometric air-fuel ratio (for example, 0°4V). The first electrode is connected between both ends of the current detection resistor 24
The output of the sensor is connected between both ends of the current detection resistor 25.
It serves as the output of the sensor. The 1i4tli voltage of the current detection resistor 24.25 is supplied to the control circuit 30. In addition,
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 (Pa) sensor 31 and a TDC balsa 3 for outputting engine speed (Ne) information are provided.
2 is provided. The Pa sensor 31 generates an output at a level corresponding to the negative pressure Ps in the intake manifold (not shown), and the TDC balsa 32 works in conjunction with the crankshaft (not shown) to generate an output every time the piston reaches top dead center. Generates a pulse. Note that the means for outputting the engine rotation speed (Ne) information includes one that generates a pulse every time the crankshaft rotates by a predetermined angle, and one that detects a pulse generated in the second coil of an ignition coil (not shown). It may be something.

The control circuit 30 includes a differential input A/D (analog/digital) converter 301 that converts the voltage across the current detection resistor 24 and 25 into a digital signal, and an A/D (analog/digital) converter 301 that converts the output signal of the Pe sensor 31 into a digital signal. /D converter 302, a waveform shaping circuit 303 that shapes the output signal of the TDC balsa 32, and the generation interval of the TDC pulse output from this waveform shaping circuit 303 by counting the clock from the clock generation circuit 304. A counter 305 for measurement, a drive circuit 306 that switches and drives the switching circuits 28 and 29, and a drive circuit 307 that drives the solenoid valve 33 to open.
, a heater current supply circuit 308 that supplies current to the heater elements 19 and 20, a CPU (central processing circuit) 309 that performs digital calculations etc. according to a program, and a ROM 31 in which various processing programs and data are written in advance.
0 and RAM311.

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, thereby enabling a Te3 interrupt when performing correction processing of the oxygen concentration sensor output, which will be described later.

In addition, the current detection resistor 24.2 which is the oxygen concentration sensor output
Pump current values 1p (1) and I p (2
) is read into the CPU 309 via the A/D converter 301.

The solenoid valve 34 is provided in a secondary intake air supply passage (not shown) that communicates with the intake manifold downstream of the engine carburetor throttle valve. Further, current is supplied to the heater element 19.20 from the heater current supply circuit 308, which causes the heater element 19.20 to generate heat and the oxygen pump element 15.1
7 and battery elements 16 and 18 are heated to an appropriate temperature higher than the exhaust gas.

In such a configuration, the exhaust gas in the exhaust pipe passes through the introduction hole 4.
The gas then flows into the first gas retention chamber 2 and diffuses therein. Furthermore, the exhaust gas in the first gas retention chamber 2 flows into the second gas retention chamber 3 through the communication hole 5 and diffuses therein.

In the switching circuits 28 and 29, as shown in FIG. 2, a switch 28a connects the electrode 11a to the current detection resistor 24, a switch 28b opens the connection line of the electrode 13a, and a switch 29a grounds the electrode 11b and connects the electrode 13b. When the connection line of the electrode 14b is opened and the switch 29b is set to the selection position where the electrode 12b is grounded and the connection line of the electrode 14b is opened, the first sensor is in the selected state.

In the selection state of the first sensor, first, when the air-fuel ratio of the air-fuel mixture supplied to the engine is in the lean region, the differential amplifier circuit 22
The output level becomes a positive level, and this positive level voltage is supplied to the series circuit of the resistor 24 and the first oxygen pump element 15. Therefore, the electrode 11a of the first oxygen pump element 15,
A pump current flows between 11b and 11b. Since this pump current flows from the electrode 11a to the electrode 11b, oxygen in the first gas retention chamber 2 is ionized at the electrode 11b, moves within the first oxygen pump element 15, and is released from the electrode 11a as oxygen gas. , the oxygen in the first gas retention chamber 2 is pumped out.

By pumping out the oxygen in the first gas retention chamber 2, a difference in oxygen concentration occurs between the exhaust gas in the first gas retention chamber 2 and the gas in the gas reference chamber 6. Due to this oxygen concentration difference, the battery element 16
A voltage Vs is generated between the electrodes 12a and 12b. This voltage Vs is supplied to the inverting input terminal of the differential amplifier circuit 22.

The output voltage of the differential amplifier circuit 22 is the voltage Vs and the reference voltage source 2.
Since the voltage is proportional to the difference voltage from the output voltage Vr+ of No. 6, 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 is the reference voltage source 2.
6 output voltage Vr+. Therefore, differential amplifier circuit 2
The output level of No. 2 is inverted from a positive level to a negative level. Due to this negative level, the electrode 11a of the first oxygen pump element 15
, 11b decreases, and the current direction is reversed. That is, the pump current flows from electrode 11b to electrode 1.
1a direction, external oxygen is ionized at the electrode 11a, moves through the 111i elementary pump element 15, and is released from the electrode 11b as oxygen gas into the first gas retention chamber 2, so that oxygen is retained in the first gas retention chamber 2. It is pumped into the sky 2. Therefore, since oxygen 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, the pump current value Ip and the output voltage of the differential amplifier circuit 22 are It is proportional to the oxygen concentration in the exhaust gas in the lean and rich regions, respectively. A solid line a in FIG. 3 indicates the pump current value Ip.

Pump current [Ip is the electric charge, 01 is the diffusion coefficient for the exhaust gas through the introduction hole 4, is σo1 is the oxygen concentration in the exhaust gas, is PO
When eXh and the oxygen concentration in the first gas retention chamber 2 are PoV, it can be expressed as in the following equation.

rp-4eao (Poexh-PoV)"-...
(1) Here, the diffusion coefficient σ0 is the area of the introduction hole 4, A is the Boltzmann constant, k is the absolute temperature, and the length of the introduction hole 4 is ρ.
, where D is the diffusion constant, it can be expressed as in the following equation.

σo=D-A/kTjl-(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 M pole 13b and Open the connection line of power supply III 1b, and also switch 2
When the electrode 9b is brought to the selected position where the electrode 14b is grounded and the connection line of the electrode 12b is opened, the second sensor is in the selected state.

In the selected state of the second sensor, the pump current is applied to the electrodes of the second oxygen pump element 17 so that the oxygen concentration in the second gas retention chamber 3 is always constant by the same operation as in the selected state of the first sensor described above. Since oxygen is supplied between 13a and 13b and pumped out, the pump current value I
P and the output voltage of the differential amplifier circuit 23 are proportional to the oxygen concentration in the exhaust gas in the lean and rich regions, respectively.

The pump current value IP in the second sensor selection state is calculated using the diffusion coefficient σ0 of the introduction hole 4 and the communication hole 5 in the above equation (1).
It is also expressed by setting PoV to be the oxygen concentration in the second gas retention chamber 3. Pump current value Ip
As shown in FIG. 4, it has been revealed that the magnitude of σ becomes smaller as the diffusion resistance, which is inversely proportional to the difference in the diffusion coefficient σ0, increases in the lean and rich air-fuel ratio regions. Therefore, the diffusion resistance is larger in the second sensor selection state than in the first sensor selection state, so the magnitude of the pump current value Ip becomes smaller in the lean and rich regions, as shown by the broken line in FIG. By adjusting the size and length of the hole 5, as shown in FIG. 3, the rich wAi+! The pump current value characteristic continues linearly with the pump current value characteristic in the lean region in the first sensor selection state at Ip=O.

In addition, the output voltage characteristics of the differential amplifier circuits 22 and 23 are also 0 (V).
becomes linearly continuous.

In the control circuit 30, processing for correcting the output signal of the oxygen concentration sensor 10 is also performed. In order to perform this sensor output correction process, the ROM 310 in the control circuit 30 is preliminarily stored with five parameters corresponding to a plurality of operating parameters of the internal combustion engine, such as engine speed Ne and intake pipe negative pressure Ps.
The correction coefficients set as shown in the figure are stored as a Ne-Pa map. Then, the CPU 309 performs sensor output correction processing according to the procedure shown in the flowchart of FIG. Note that this correction processing is performed by a T2C interrupt in a routine that is processed for each ignition in engine control.

The CPU 309 first receives the TDC from the waveform shaping circuit 303.
Interrupt processing is performed by a T2C interrupt caused by a pulse (step 1). Then, the pump current value I flowing through the current detection resistor 24.25 which is the output of the oxygen concentration sensor 10
P (1) and I p (2) are read (step 2), and then the current TDC timing is changed from the previous TDC timing.
The engine rotation speed Ne is measured based on the count counted by the counter 305 up to the DC timing (Step 3), and the output voltage of the intake pipe negative pressure sensor 37 is read (Step 4). A correction coefficient corresponding to the detected engine speed Ne and intake pipe negative pressure Pa is obtained from the Ne-Pa map in the ROM 310, 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 PB is large, that is, when the intake air IQa is small. It is set to be small (for example, 0.8 times) when the number Ne is high and the intake pipe negative pressure P8 is small, that is, when the intake air ff1Qa is large.

Through the above series of steps, the sensor output is corrected, and this allows for complex temperature control of the heater elements 19 and 20, and for making the structure of the sensor body complicated by attaching multiple protective covers to the sensor body. Even if you don't, ROM3
By simply changing the program No. 10 and storing the Ne-Pe map in advance, it is possible to obtain a sensor output that is independent of changes in exhaust temperature and flow rate.

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

Further, in the above embodiment, the correction coefficient is stored in advance in the ROM 310 as a Ne-Pa map, and the correction coefficient corresponding to the detected engine speed Ne and intake pipe negative pressure PB is read out from the map in the ROM 310 and corrected. However, a correction coefficient is obtained by calculating a predetermined calculation formula based on the engine rotation speed Ne and intake pipe negative pressure PB detected by the CPU 309, and correction is performed based on this correction coefficient. is also possible.

Furthermore, the oxygen concentration detection sensor used in the oxygen concentration detection device according to the present invention is shown in FIG. 1(a).

It is not limited to the structure shown in (b).

As explained above, the oxygen concentration detection device according to the present invention detects a plurality of operating parameters of an internal combustion engine, obtains correction coefficients based on these operating parameters, and determines the oxygen concentration based on the correction coefficients. Since it is configured to correct the output signal of the sensor, there is no need for complicated temperature control of the heater, and there is no need to complicate the structure of the sensor body.
It is possible to obtain a detection output that is independent of changes in exhaust temperature and flow rate. Therefore, it is possible to prevent variations in the detected air-fuel ratio due to exhaust gas temperature dependence and exhaust flow rate dependence, thereby improving the accuracy of air-fuel ratio control.

[Brief explanation 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 a plan view showing an embodiment of the oxygen concentration detection device according to the present invention.
2 is a circuit diagram showing the current supply circuit including the air-fuel ratio 1IIJ III device, 3 is a diagram showing the output characteristics of the device in 1, and 4 is the diffusion resistance and pump current. FIG. 5 is a diagram showing an example of the correction coefficient of the Ne-Pa map, and FIG. 6 is a flowchart showing the procedure for correcting the output of the oxygen concentration sensor. 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 to 10...Oxygen concentration sensor 15.17 ...Oxygen pump element 16.18...
...Battery element 19.20...Heater element 21...Current supply circuit 30...Control circuit

Claims (2)

[Claims] (1) An oxygen concentration detection device for an internal combustion engine, which includes an oxygen concentration sensor installed in the exhaust system of the internal combustion engine to detect the oxygen concentration in the exhaust gas and generate an output signal proportional to the oxygen concentration, the device comprising: It is characterized by comprising means for detecting a plurality of operating parameters of the internal combustion engine, and means for obtaining a correction coefficient based on the plurality of operating parameters and correcting the output signal of the oxygen concentration sensor based on the correction coefficient. Oxygen concentration detection device for internal combustion engines. (2) The oxygen concentration detection device for an internal combustion engine according to claim 1, wherein the correction coefficient is stored in a memory in advance in correspondence with the plurality of operating parameters.