JPS6255555A - Air/fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To achieve a higher operability where the air/fuel ratio is controlled to a value in the vicinity of the theoretical air/fuel ratio, by stopping the supply of current to an oxygen pump element when a target air/fuel ratio is set below a specified value. CONSTITUTION:An oxygen concentration detector has a pair of oxygen ion conductive solid electrolytic materials each having a pair of electrodes arranged as opposed to each other in an emission gas of an internal combustion engine through a specified clearance part 3; one thereof acts as oxygen pump element 1, and the other as battery element 2 for measuring oxygen concentration ratio. A current supply circuit 11 supplies current to electrodes 5 and 6 of the element 1. Then, a control circuit 31 discriminates the air/fuel ratio of a mixed gas fed to the engine according to a voltage generated between electrodes 7 and 8 of the element 2. A target air/fuel ratio is set for the supply mixed gas and according to the results of the discrimination, the air/fuel ratio of the supply mixed gas is adjusted. When the target air/fuel ratio is below a specified value, the supply of current to the element 1 is stopped by the circuit 11.

Description

[Detailed description of the invention] Itgoko 1 The present invention relates to an air-fuel ratio control device for an internal combustion engine.

FI in the exhaust gas for the purpose of purifying the exhaust gas of m-ball internal combustion engines and improving fuel efficiency! There is an air-fuel ratio control device that detects the elementary concentration and performs feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine to a target air-fuel ratio according to the detection result.

As an oxygen concentration detection device used in such an air-fuel ratio control device, there is a device that generates an output proportional to m degrees in the gas to be measured (Japanese Patent Laid-Open No. 153155/1983). Such an R desertity detection device is provided with an oxygen concentration detection device having a pair of flat oxygen ion conductive solid electrolyte materials.

The solid electrolyte material is placed in the gas to be measured, and electrodes are formed on each surface of the solid electrolyte material, and the solid electrolyte materials are arranged in parallel so as to face each other with a predetermined gap in between. It is located. One side of the solid electrolyte material serves as an oxygen pump element, and the other! ! It is designed to function as a battery element for measuring the elemental temperature ratio. J3 in the gas to be measured
When a current is supplied between the electrodes of the oxygen pump element so that the electrodes on the gap side become square, the oxygen gas in the gap is ionized on the negative electrode side of the oxygen pump cord, and the inside of the oxygen pump element is ionized. It moves to the positive electrode side and is released as oxygen gas from the 1-electrode surface. At this time, due to the decrease in oxygen gas in the gap, an oxygen m difference occurs between the gas in the gap and the gas outside the battery element, so II! If the current supplied to the dual pump element is constant, the oxygen concentration difference between the electrodes of the battery element,
In other words, a voltage proportional to the oxygen concentration in the gas to be measured is generated.

Based on the voltage generated by the battery element, it is determined whether the air-fuel ratio of the air-fuel mixture supplied to the engine is ridge or lean based on the target air-fuel ratio. When controlling the air-fuel ratio using secondary air, if it is determined to be rich, secondary air is supplied to the engine, and if it is determined to be lean, the supply of secondary air is stopped, thereby achieving the target air-fuel ratio. Controlled by air fuel ratio.

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 material.

For example, when Zr0z (zirconium oxide) is used as the solid electrolyte material, oxygen 02 is taken away from ZrO2 by excessive current supply to the oxygen pump element, and zirconium Zr is precipitated. This blackening phenomenon is caused by Pi
! This causes rapid deterioration of the cable pump element and deteriorates its performance as an oxygen concentration detector.

Figure 1 shows the relationship between the Pa concentration and the current value Ip supplied to the R element pump element and the blackening phenomenon occurrence region using the voltage Vs generated in the battery element as a parameter. Since the boundary line is a linear functional characteristic similar to the relational characteristic using the voltage Vs as a parameter, it is possible to determine from the voltage Vs whether the current supplied to the oxygen pump element belongs to the value in the blackening phenomenon occurrence region. can. Therefore, when the voltage Vs exceeds a voltage slightly smaller than the boundary voltage of the blackening phenomenon occurrence region, the supply current to the oxygen pump element is reduced to a value close to the blackening phenomenon occurrence region. This makes it possible to prevent the blackening phenomenon from occurring.

However, when such an oxygen concentration detection device is applied to an air-fuel ratio control device, when the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to a target air-fuel ratio near the stoichiometric air-fuel ratio (14,7> It was found that the voltage fluctuated violently up and down, becoming very unstable, and dropping below the voltage level during normal detection.As a result, the air-fuel ratio could not be accurately determined from the output voltage Vs of the oxygen concentration detection device, and the If the air-fuel ratio of the supplied air-fuel mixture is controlled according to the result, drivability deteriorates.

An object of the present invention is to provide an air-fuel ratio control device that improves drivability when the air-fuel ratio is controlled to a value near the stoichiometric air-fuel ratio.

The air-fuel ratio control device of the present invention is characterized in that when the target air-fuel ratio is set below a predetermined value, the current supply to the oxygen pump element is stopped to prevent incorrect air-fuel ratio determination.

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

FIG. 2 shows an air-fuel ratio control device according to the present invention. In this apparatus, at t3, an oxygen concentration detector consisting of a pair of parallel planar elements, the oxygen pump cord 1 and the battery element 2, is disposed in 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,
The other ends are connected to each other via a spacer 4. Further, rectangular electrode plates 5 to 8 made of porous heat-resistant fully bendable material are provided on the front and back surfaces of one end of the oxygen pump element 1 and the battery element 2, and the electrode plates 5 to 8 are provided on the other end surface. Out F
i15a to i8a are formed.

A constant current circuit 11 is connected between the electrode plates 5 and 6 of the oxygen pump element 1.
A constant current is supplied from the The constant current circuit 11 is a sink type circuit, and the operational amplifier 12. NPN transistor 13
and resistors 15 to 17. The output terminal of the operational amplifier 12 is connected to the base of the transistor 13 via a resistor 15.

Further, the emitter of the transistor 13 is grounded via a resistor 16 and connected via a resistor 17 to the inverting input terminal of the operational amplifier 12. The collector of the transistor 13 is connected to the inner electrode plate 6 of the oxygen pump element 1 by a lead wire 6a.
A voltage VB is supplied to the outer electrode plate 5 via a lead wire 5a.

On the other hand, the inner electrode plate 7 of the battery element 2 is grounded via a lead wire 7a, and the outer electrode plate 8 is connected to a filter circuit 19 via a lead wire 8a. Filter circuit 1
9 is the resistance 20. It consists of a capacitor 21 and is designed to remove noise components of the voltage signal generated between the electrode plates 7 and 8 of the battery element 2. An operational amplifier 26. is connected to the output end of the filter circuit 19. It is connected to the Vs" input terminal of an air-fuel ratio control circuit 31 via a non-inverting amplifier 30 consisting of resistors 27 to 29. A D/A converter 32 is connected to an IC control output terminal of the air-fuel ratio control circuit 31. , the D/A converter 32 generates a voltage according to the digital signal output from the Ic control output terminal of the air-fuel ratio 1.111110 path 31.
The output terminal of the A converter 32 is connected to the non-inverting input terminal of the operational amplifier 12 via a voltage follower circuit 33 consisting of an operational amplifier and a resistor 34.

Further, a limiter circuit 38 is connected to the output terminal of the non-inverting amplifier 30. The limiter circuit 38 includes an operational amplifier 39.
Resistance 40, 41. Diode 42 and limiter reference voltage generation? Consists of h43. The inverting input end of the operational amplifier 39 is connected to the output end of the limiter reference voltage generator 43, and the non-inverting input end is connected to the output end of the non-inverting amplifier 30. The operational amplifier 39 supplies a voltage corresponding to the difference voltage between the output voltage of the non-inverting amplifier 30 and the limiter reference voltage VL output from the limiter reference voltage generator 43 to the inverting input of the operational amplifier 12 through a resistor 41° diode 42 in the forward direction. It is designed to be fed at the end.

The air-fuel ratio control circuit 31 has an A/F drive end in addition to the above-mentioned Ic output end and VS' input end, and the A/F drive end is connected to a solenoid valve 44 for adjusting secondary air supply. ing. The solenoid valve 44 is provided in a secondary intake air supply passage that communicates with the intake passage downstream of the carburetor throttle valve of the engine.

In such a configuration, when a digital signal is output from the Ic output terminal of the air-fuel ratio control circuit 31 to the D/A'ilL converter 32, the digital signal is converted into a voltage by the D/A converter 32, and the digital signal is converted into a voltage. The voltage is the voltage follower circuit 33
, and is supplied to the non-inverting input terminal of the operational amplifier 12 via the resistor 34 as a reference voltage Vr+. Reference voltage Vr+
The pump current value 4p that flows between the electrode plates 5 and 6 of the oxygen pump element 1 when is supplied is detected by the terminal voltage ρ of the resistor 16, and the terminal voltage Vp is supplied to the inverting input terminal of the operational amplifier 120 via the resistor 17. be done. When the terminal voltage Vp is lower than the reference voltage Vr+, the output level of the operational amplifier 12 becomes high level and the base current of the transistor 13 is prevented from increasing, so the pump current 1p increases and the terminal voltage Vp
When Vr+ is greater than the reference voltage Vr+, the output level of the operational amplifier 12 becomes a low level, which reduces the base current of the transistor 13, thereby reducing the pump current. Since this operation is repeated at high speed, a constant current value is obtained according to the pump current 1p11 base voltage vrI.

On the other hand, voltage VS is generated on electrode plates 7.8 of battery element 2, and voltage Vs is supplied to non-inverting amplifier 30 via filter circuit 19. The non-inverting amplifier 30 is the filter circuit 1
9 is amplified and supplied to the Vs'' input terminal of the air-fuel ratio control circuit 31 as an oxygen concentration detection output.

The air-fuel ratio control circuit 31 operates in synchronization with engine rotation as follows. As shown in FIG. 3, first, the air-fuel ratio control circuit 3
1 sets a target air-fuel ratio DA/' to which value the air-fuel ratio of the supplied air-fuel mixture should be controlled according to the operating state of the engine (step 51).

The target air-fuel ratio DA/F is set, for example, from the engine speed and the engine intake pipe pressure, and is retrieved from a data map stored in advance in a ROM or the like in the air-fuel ratio control circuit 31. After setting the target air-fuel ratio DA/F, the target air-fuel ratio DA
It is determined whether 7F is a person based on a predetermined value [)r (step 52). The predetermined value Or is a value slightly different from the stoichiometric air-fuel ratio. If OA/F≦[)r, even if the target air-fuel ratio is set near the stoichiometric air-fuel ratio or richer than it, it is not possible to accurately determine the air-fuel ratio from the pump current, so the reference voltage Vr+ is set to stop the pump current supply. The content of the digital signal output from the Ic control output terminal is changed to "O" so as to make the voltage O(V), for example, "o o o o" in the case of a 4-bit digital signal (step 53). ). When the reference voltage Vr+ is set to 0 (V), the output level of the operational amplifier 12 becomes a low level, so the 1- transistor 13 is turned off, and the electrode plate 5.6 of the oxygen pump element 1 is turned off.
Pump current stops flowing during this period. After executing step 53, the air-fuel ratio control circuit 31 stops driving the solenoid valve 44 to open in order to stop supplying secondary air to the engine (step 54). On the other hand, if DA/F>Dr, the target air-fuel ratio is set leaner than near the stoichiometric air-fuel ratio, and the digital signal output from the Ic control output terminal is set to a predetermined oxygen concentration detection signal to supply pump current. (step 55). Then, the output voltage Vs- of the non-inverting amplifier 30 is read (step 56), and the read output voltage Vs' is the reference voltage V corresponding to the target air-fuel ratio, /.
It is determined whether it is greater than r2 (step 57).

If Vs=>yr2, the air-fuel ratio of the air-fuel mixture supplied to the engine is a lip, and the air-fuel ratio control circuit 31 opens the solenoid valve 44 to supply secondary air to the engine (step 58). If VS-≦V r 2, it is assumed that the air-fuel ratio of the supplied air-fuel mixture is lean, and step 54 is executed to stop the supply of secondary air to the engine.

Further, when the voltage Vs between the electrode plates 7.8 of the battery element 2 increases, the output voltage Vs= of the non-inverting amplifier 30 increases. When the output voltage Vs' exceeds the limiter reference voltage v, the voltage corresponding to the difference voltage between the output voltage Vs' and the limiter reference voltage VL becomes higher than the terminal voltage Vp, so that the operational amplifier 39 is connected to the resistor 41. Diode 42. A current flows through the resistor 17 and then through the resistor 16, causing the voltage at the inverting input terminal of the operational amplifier 12 to rise above the reference voltage Vr+.Thus,
The output voltage of the operational amplifier 12 decreases and the transistor 13
Since the base current of the oxygen pump element 1 decreases, the pump current 1p of the oxygen pump element 1 also decreases. Since the limiter reference voltage VL is set slightly higher than the reference voltage ■r2, the output voltage Vs- of the non-inverting amplifier 30 becomes the limiter reference. When the voltage reaches VL, it means that the area where the blackening phenomenon occurs is approached 11'. When Vs->VL, the higher the air-fuel ratio is, the higher the output voltage of the operational amplifier 39 becomes, and the pump current Tp increases.
This prevents the blackening phenomenon from occurring.

In the embodiment of the present invention described above, when the target air-fuel ratio DA/F is smaller than the predetermined value [)r, the supply of the pump Ti flow is stopped by changing the content of the digital signal. Not limited to, just an example.

For example, the voltage at the non-inverting input terminal of the operational amplifier 12 is forced to 0 (
V) may also be used. Furthermore, if the target air-fuel ratio DA/F is retrieved from the memory in the control circuit 31 at the output voltage level of the l'ill depth detection concentration, the retrieved target air-fuel ratio DA/F is directly used as the reference voltage Vr2. Can be used.

As described above, the air-fuel ratio control of the internal combustion engine of the present invention 2I!
In the device, the output of the M wood degree detection device becomes unstable. l! When a target air-fuel ratio near the theoretical air-fuel ratio is set, the current supply to the oxygen pump element is stopped, thereby avoiding the occurrence of the blackening phenomenon and preventing rapid deterioration of the oxygen pump element. . Further, it is possible to prevent incorrect air-fuel ratio determination based on the output voltage of the oxygen a degree detection device.

Therefore, it is possible to improve the drivability of the engine when the air-fuel ratio is around the stoichiometric air-fuel ratio.

[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 circuit diagram showing the air-fuel ratio control device according to the present invention, and Fig. 3 is a diagram showing the control circuit in the device of Fig. 2. It is a flow diagram showing the behavior. Explanation of symbols of main parts 1...Oxygen pump element 2...Battery element 3...Gap portion 4...Spacer 5 to 8...・Electrode plate 11... Constant current circuit 30... Non-inverting amplifier 38... Limiter circuit Applicant Honda Motor Co., Ltd., Agent Patent attorney Motohiko Fujimura Figure 1 Oxygen concentration

Claims (1)

[Claims] A pair of oxygen ion conductive solid electrolyte materials disposed in the exhaust gas of an internal combustion engine, a pair of electrodes formed on each of the solid electrolyte materials, and the pair of solid electrolyte materials are connected to each other through a predetermined gap. A current is supplied between an electrode of the oxygen pump element and an oxygen concentration detector arranged to face each other, one of the pair of solid electrolyte materials acts as an oxygen pump element and the other acts as a battery element for measuring oxygen concentration ratio. a current supply means; a determination means for determining an air-fuel ratio of the air-fuel mixture supplied to the engine according to a voltage generated between the electrodes of the battery element; and a determination means for setting a target air-fuel ratio of the air-fuel ratio of the supplied air-fuel mixture; and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the supplied air-fuel mixture to a target air-fuel ratio according to the determination result of the means, and the current supply means supplies current to the oxygen pump element when the target air-fuel ratio is below a predetermined value. An air-fuel ratio control device characterized by stopping supply.