JPS6271853A - Oxygen concentration detector - Google Patents

Abstract

PURPOSE:To prevent securely a blackening phonomenenon from occurring by stopping supplying a pump current to an oxygen pump element when the value of a supply current to the oxygen pump element exceeds a limit value. CONSTITUTION:A signal from a terminal Ic of an air-fuel ratio control circuit 32 enters the charging/discharging part of an integration circuit 28 through a D/A converter 26 and a follower circuit 27 and is raised in voltage according to a time constant and inputted to the uninverted input part of an amplifier 12. The inverted input of the amplifier 12, on the other hand, is at a low level, so the amplifier 12 generates a high-level output to turn on a transistor TR 13, and a pump current flows between electrodes 5 and 6 of the pump element 1, so that a voltage VS is developed between electrodes 7 and 8 of a battery element. When the output voltage of the amplifier 21 reaches the specific value, the noninverting amplifier 25 amplifies the VS and supplies it to the inverted input terminal of the amplifier 12. Then, the state is inverted and the TR 13 is turned off to stop a pump current, so that the VS stops. Thus, said operation is repeated at a high speed to control the voltage VS to a constant level.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen Q degree detection device for detecting the oxygen concentration in gas such as engine exhaust gas.

For the purpose of purifying the exhaust gas of internal combustion engines and improving fuel efficiency, the oxygen concentration in the exhaust gas is detected, and the air-fuel ratio of the mixture supplied to the engine is feedback-controlled to the target air-fuel ratio according to the detection results. There is an air-fuel ratio control device that does this.

As an oxygen concentration detection device used in such an air-fuel ratio control device, there is one that generates an output proportional to the oxygen f1 degree in the gas to be measured (Japanese Patent Laid-Open No. 153155/1983). In such an oxygen WJ degree detection device, a pair of flat M
An M elementary concentration detector having an M ion-conducting solid electrolyte member is provided.

The solid electrolyte member is arranged in the gas to be measured, and electrodes are formed on each front and back surface of the solid electrolyte member, and the solid electrolyte member is flattened so as to face -C through a predetermined gap. It is located in One of the solid electrolyte members acts as an oxygen pump element, and the other acts as a battery element for oxygen temperature ratio measurement. When a current is supplied between the electrodes of the oxygen pump element so that the gap side electrode becomes the negative electrode in the gas to be measured, the oxygen gas in the gap gas is ionized on the negative electrode side of the oxygen pump element, and the oxygen pump It moves within the device toward the positive electrode surface and is released from the positive electrode surface as oxygen gas. This moment is in the gap! ll between the gas in the gap and the gas outside the battery element due to the decrease in elementary gas! Since there is a difference in concentration between the two prefectures, a voltage is generated between the electrodes of the battery element. If the pump current value supplied to the oxygen pump element is changed to maintain this voltage at a constant value, the pump current value will be approximately proportional to the oxygen concentration in the gas being measured at a constant temperature, and the detected oxygen humidity value will be is output as

In such an oxygen concentration detection device, when an excessive current is supplied to the oxygen pump element, a blackening phenomenon occurs in which oxygen is taken away from the solid electrolyte member.

For example, when ZrO2 (zirconium dioxide) is used as the solid electrolyte member, oxygen 02 is taken away from ZrO2 by excessive current supply to the oxygen pump element, and zirconium Zr is deposited. This blackening phenomenon causes deterioration of the M pump element.

This will cause the oxygen concentration detector to deteriorate in performance.

Figure 1 shows the relationship between the oxygen concentration and the current supplied to the oxygen pump element and the area where the blackening phenomenon occurs, using the voltage Vs generated in the battery element as a parameter, and the boundary line with the area where the blackening phenomenon occurs is the voltage Since it is a linear functional characteristic similar to the relational characteristic using Vs as a parameter, it can be determined from the voltage Vs whether the current supplied to the oxygen pump element belongs to the value in the blackening phenomenon occurrence region. Therefore, when the voltage Vs increases to a predetermined voltage or higher, the current supplied to the oxygen pump element becomes a value close to the area where the blackning phenomenon occurs, and by reducing the supplied current, it is possible to prevent the occurrence of the blackning phenomenon. .

In an air-fuel ratio control device using such an oxygen m degree detection device, the value of the current supplied to the WIA cable pump element is set to a value below the blackning phenomenon occurrence boundary value in order to prevent the blackning phenomenon, and the W1 By comparing the current value supplied to the elementary pump element and the half value of M, it is determined whether the air-fuel ratio of the supplied air-fuel mixture is the target air-fuel ratio J: rich or lean. In the case of a system in which the air-fuel ratio is controlled by secondary air, if the engine is determined to be rich, secondary air is supplied to the engine, and if the engine is determined to be lean, the secondary air supply is stopped. The fuel ratio is controlled to the target air-fuel ratio.

As a current supply means for supplying pump current to the oxygen pump element, a current supply circuit is used which compares the voltage generated between the electrodes of the battery element with a reference voltage and controls the current supplied to the oxygen pump element according to the comparison result. There is. When the reference voltage is supplied to the current supply circuit as shown in Fig. 2 (a) at the time of starting the engine, etc., the current supply circuit starts supplying pump current to the oxygen pump cord. However, the operation of the air-fuel ratio control system Due to the delay, the pump current does not immediately reach the current value within the predetermined control range, but changes transiently as shown in Figure 2 (b), causing an overshoot, so that the pump current value does not exceed the blackning phenomenon occurrence boundary value. - There was a problem in that the blackening phenomenon could occur due to heat.

In addition, since there is a gap between the oxygen pump element and the battery element, even if the pump current value rises to a current value within the predetermined control t11 range immediately after the start of pump current supply to the oxygen pump element, the response will be delayed. The output voltage of the battery element does not reach around the reference voltage immediately, but gradually rises as shown in FIG. 2 <C). Therefore, in order to prevent the occurrence of the blackning phenomenon, even if the device is designed to determine from the output voltage of the battery element whether an excessive current is flowing through the oxygen pump element, which would cause the blackning phenomenon to occur, the pump' cannot be supplied with current. It was not possible to completely prevent the blackening phenomenon from occurring immediately after starting.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an oxygen concentration detection device that can reliably prevent the blackening phenomenon immediately after the start of pump supply.

The oxygen concentration detection device of the present invention includes a limit command means that generates a flow stop command when the supply pump current value reaches a limit value or more, a reference voltage generation means that generates a reference voltage, and a charge pump that is charged by the reference voltage. and a charging/discharging circuit that discharges its charge in response to a current stop command, and a current is supplied between the electrodes of the oxygen pump element so that the voltage between the electrodes of the battery element is equal to the output voltage of the charging/discharging circuit. The present invention is characterized by being provided with a current supply means comprising a current supply circuit that stops supplying current between the electrodes of the oxygen pump element in response to a stop command.

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

FIG. 3 shows an air-fuel ratio control device using the oxygen concentration detection device according to the present invention. In this device, an oxygen concentration detector consisting of a pair of planar elements parallel to each other, an oxygen pump element 1 and a battery element 2, is disposed within an exhaust pipe (not shown). The main body of the oxygen pump element 1 and the battery element 2 is made of an oxygen ion conductive solid electrolyte material, and a gap 3 is formed between one end thereof, and the other end thereof is connected to each other via a spacer 4. Also, oxygen pump element 1 and battery element 2
Rectangular electrode plates 5 to 8 made of porous heat-resistant metal are provided on the front and back surfaces of one end, and drawers 15a to 8a of the Fi electrode plates 5 to 8 are formed on the other end.

A current supply circuit 1 is connected between the electrode plates 5 and 6 of the oxygen pump cord 1.
Current is supplied by 1△. The current supply circuit 11 includes an operational amplifier 12. NPN transistor 13 and resistor 14.1
Consists of 5. The output end of the operational amplifier 12 is connected to the base of a transistor 13 via a resistor 14. Also, the transmitter of the transistor 13 is grounded via a resistor 15.

The resistor 15 is provided to detect the pump current value 1p flowing between the electrode plates 5 and 6 of the oxygen pump element 1, and its terminal voltage is used as the pump current value IP in the air-fuel ratio control circuit 3.
2 of 1 + - supplied to human power #4.

The collector of the transistor 13 is connected to the inner electrode plate 6 of the oxygen pump element 1 via a lead wire 6a, and the voltage v8 is supplied to the outer electrode plate 5 via the lead wire 5a. There is. Further, a Zener diode 18 is connected in parallel between the collector and emitter of the transistor 13 with its cathode facing the collector side of the transistor 13.

The Zener diode 18 is provided to prevent a voltage higher than the withstand voltage from being applied between the collector and emitter of the transistor "!3".

On the other hand, the inner electrode plate 7 of the battery element 2 is grounded via the lead wire 7a, and the outer electrode plate 8 is grounded via the lead wire 7a.
through the operational amplifier 21. Itj, anti-22 to 24
It is connected to a non-inverting amplifier 25 consisting of. The output of the non-inverting amplifier 25 is connected to the inverting input terminal of the operational amplifier 12. A D/A converter 26 is connected to the Ic control output terminal of the air-fuel ratio control circuit 32, and the D/A converter 26 receives Vs output from the Ic control output terminal of the air-fuel ratio control circuit 32.
Generates voltage according to value command data. D/A converter 2
The output terminal of 6 is connected to an integrating circuit 28 forming a charging/discharging circuit via a voltage follower circuit 27 consisting of an operational amplifier. The integrating circuit 28 is composed of a resistor 29, 30 and a capacitor 31, and its output voltage is supplied to the non-inverting input terminal of the operational amplifier 12.

The air-fuel ratio control circuit 32 is preferably composed of a microcomputer, and in addition to the above-mentioned 1c output terminal and Ip input terminal, it has an A/F output terminal.
It has an F drive end and an Io output end, and the A/F drive end is connected to a solenoid valve 39 for adjusting secondary air supply. The solenoid valve 39 is provided in a secondary intake air supply passage that communicates with the intake passage downstream of the carburetor throttle valve of the engine. A switch circuit 40 is connected to the Io output terminal. The switch circuit 40 consists of resistors 41, 42 and a transistor 43.

The transistor 43 is turned on when a current stop command is supplied from the 1o output terminal of the air-fuel ratio control circuit 32, and the integrator circuit 2
The terminal of the resistor 29 of 8 is short-circuited to the ground line, and the base of the transistor 13 is short-circuited to the ground line.

In this configuration, when Vs value command data is output from the Ic output terminal of the air-fuel ratio control circuit 32 to the D/A converter 26 at time t1, the D/A converter 26 outputs Vs value command data.
The s value command data is converted to the control m royal pressure VC, and the control m +
The voltage VC is connected to the voltage follower circuit 2 as shown in FIG.
7 to an integrating circuit 28. As shown in FIG. 1, the output voltage of the integrating circuit 28 gradually increases due to the integration time constant formed by the resistor 29.30 and the capacitor 31, and after a predetermined time Ti from time t1, the voltage M is controlled by the resistor 29.30. The divided voltage of VC is reached. This divided voltage is the integral output voltage! It is supplied as IVr+ to the non-inverting input terminal of the η bare amplifier 12. At this time, since the voltage level at the inverting input terminal of the operational amplifier 12 is smaller than the integrated output voltage Vr+, the output level of the operational amplifier 12 becomes high level, and the transistor 13 is turned on. When the transistor 13 is turned on, a pump current flows between the electrode plates 5 and 6 of the oxygen pump element 71.

When the pump current flows, a voltage Vs is generated between the electrode plates 7° and 8 of the battery element 2, and the voltage Vs gradually increases from time t1 as shown in FIG. A predetermined voltage level is reached immediately. Also, the voltage Vs
is supplied to a non-inverting amplifier 25, which amplifies the voltage Vs and supplies it to the inverting input terminal of the operational amplifier 12.

When the voltage Vs increases, the output voltage V of the non-inverting amplifier 25
s- also increases. The output voltage Vs- is the integrated output voltage Vr+
When the voltage exceeds 0, the output level of the operational amplifier 12 is inverted to a low level, and the transistor 13 is turned off. transistor 1
3 is turned off, the pump current decreases, so the voltage Vs generated between the electrode plates 7 and 8 of the battery element 2 decreases, and the voltage VS' supplied from the non-inverting amplifier 25 to the inverting input terminal of the operational amplifier 12 also decreases. When the voltage Vs- falls below the integrated output voltage Vr1, the output level of the operational amplifier 12 becomes high level again, causing the pump current to increase. Since this operation is repeated at high speed, the voltage Vs is controlled to a constant value and becomes a voltage directly corresponding to the Vslif4 command data.

The pump current value 1 flowing between the electrode plates 5 and 6 of the oxygen pump element 1 when the integral output voltage Vr+ is supplied to the operational amplifier 12
p is detected by the terminal voltage Vp of the resistor 15, and the terminal voltage Vp is supplied to the Ip input terminal of the air-fuel ratio control circuit 32.

The air-fuel ratio control circuit 32 changes l01l'IJl to engine rotation.
It operates as follows. As shown in FIG. 5, first, it is determined whether air-fuel ratio feedback (F/B) control conditions are satisfied (step 51).

This determination is determined from various engine parameters such as engine rotational speed, intake pressure, and cold water temperature. Note that a plurality of sensors (not shown) are provided to detect these engine parameters. When the air-fuel ratio feedback control conditions are not satisfied, for example, when the engine is under high load,
When the cooling water temperature is low, a current stop command consisting of a high level signal is generated to the switch circuit 40 (step 52). In response to the current stop command, the transistor 43 of the switch circuit 40 is turned on and the base of the transistor 13 is brought to the ground level. Therefore, the transistor 13 is turned off, stopping the supply of pump current between the electrode plates 5 and 6 of the oxygen pump element 1. Also, the input line from the voltage follower circuit 27 to the integrating circuit 28 is made equal to the ground level. Therefore, current flows from the capacitor 31 to the ground via the resistor 29 or t-30, and the charge accumulated in the capacitor 9'31 is discharged, so that the output voltage of the integrating circuit 28 gradually decreases.

On the other hand, if the air-fuel ratio feedback control conditions are satisfied, the generation of the current stop command is stopped (step 5
3). The transistor 43 stops generating the current stop command.
is turned off and voltage is supplied from the voltage follower circuit 27 to the integrating circuit 28, so the capacitor 31 is charged and the terminal voltage of the capacitor 31, that is, the output voltage of the integrating circuit 28, gradually rises to 11. When the transistor 43 is turned off, the base level of the transistor 13 is released from the ground level, and the current supply circuit 11 receives the output of the integrating circuit 28.
The pump current is applied to the electrode plate 5 of the oxygen pump element 1 according to the withstand pressure.
, 6, the pump current value IP suddenly increases to a value corresponding to the output voltage of the integrating circuit 28 immediately after the generation of the current stop command stops, and then gradually increases. Note that if this step 53 satisfies the air-fuel ratio feedback control condition and has already been executed at step 10, then the air-fuel ratio feedback control condition is satisfied.
It may be ignored until the back control condition is no longer satisfied. Thereafter, a limit value TPL of the pump current value 1p is set according to the target air-fuel ratio at this time (step 54
). For example, the limit value fpL is retrieved from a data map stored in advance in a ROM in the air-fuel ratio control circuit 32. When the limit value fpL is set to 1 pL, the pump current EI
T "How is the terminal voltage Vp read (Step 5?
5) The read pump current value ρ is the limit
It is determined whether or not it is greater than lIlpL (step 56).

If Ip>IpL, there is a possibility that a blackening phenomenon will occur, so step 52 is executed and the supply of pump current is stopped. If Ip≦IPL, the read pump current value Tp is the reference value 1. corresponding to the target air-fuel ratio. j″
It is determined whether or not it is smaller than ' (step 57).

If Ip<Ir, the air-fuel ratio of the air-fuel mixture supplied to the engine is rich, and the air-fuel ratio control circuit 32 controls the solenoid valve 3.
9 to open the valve to supply secondary air to the engine (
Step 58). If lp≧lr, it is assumed that the air-fuel ratio is equal to one, and the air-fuel ratio control circuit 32 stops driving the solenoid valve 39 to open, and the supply of secondary air to the engine is stopped (
Step 59). Furthermore, when step 52 is executed, step 59 is executed and the supply of secondary air to the engine is stopped.

As described above, in the oxygen concentration detection device of the present invention, when the supply current value to the oxygen pump element is equal to or higher than the limit value, the supply of pump current to the oxygen pump element is stopped, so that the secondary air supply is Even if there is a time delay until the air-fuel ratio control result is detected based on the oxygen concentration in the exhaust gas, the black tan phenomenon can be reliably prevented from occurring. In addition, since the pump current gradually increases immediately after the start of pump current supply to the oxygen pump element, the gap between the oxygen pump element and the battery element causes a delay in the response to the excessive pump current prevention operation by a limiter circuit, etc. It is also possible to prevent the pump current from reaching a value in the range where the blackening phenomenon occurs.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the oxygen concentration-pump current characteristics and the blackening phenomenon occurrence region, Fig. 2 is a waveform diagram showing the operation of a conventional oxygen concentration detection device, and Fig. 3 is a diagram showing the operation of a conventional oxygen concentration detection device. FIG. 4 is a waveform diagram showing the operation of the device shown in FIG. 3, and FIG. 5 is a flow chart showing the operation of the four control paths in the device shown in FIG. 3. Explanation of symbols of main parts 1...Oxygen pump element 2...Battery element 3...Gap portion 4...Spacer 5 to 8...・Electrode plate 11...Current supply circuit 25...Non-inverting amplifier

Claims (1)

[Claims] A pair of oxygen ion conductive solid electrolyte members disposed in a gas to be measured, a pair of electrodes formed on each of the solid electrolyte members, and the pair of solid electrolyte members facing each other with a predetermined gap interposed therebetween. an oxygen concentration detector arranged in such a manner that one of the pair of solid electrolyte members acts as an oxygen pump element and the other acts as a battery element for measuring oxygen concentration ratio; and a current supply that supplies current between the electrodes of the oxygen pump element. and outputting the supplied current value of the current supplying means as an oxygen concentration detection value, the current supplying means issuing a current stop command when the supplied current value reaches a limit reference value or more. a limit command means for generating a reference voltage, a reference voltage generating means for generating a reference voltage, a charging/discharging circuit that is charged by the reference voltage and discharges the charged charge in response to the current stop command, and a voltage between the electrodes of the battery element. supplying a current between the electrodes of the oxygen pump element so that the voltage of the voltage becomes equal to the output voltage of the charging/discharging circuit, and stopping the current supply between the electrodes of the oxygen pump element in response to the current stop command; An oxygen concentration detection device characterized by comprising a circuit.