JPS6255554A - Air/fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To elevate the operability when the air/fuel ratio is controlled to be in the vicinity of the theoretical air/fuel ratio, by stopping the supply of current to an oxygen pump element when the target air/fuel ratio is below a specified value. CONSTITUTION:An oxygen concentration detector has a pair of oxygen ions conducting 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 element 2 for measuring oxygen concentration ratio. A current supply circuit 11 supplies current between electrodes 5 and 6 of the element 1 and changes the supply current value to keep the voltage at a constant value as generated between electrodes 7 and 8 of the element 2. Then, a control circuit 31 discriminates the air/fuel ratio of a mixed gas supplied to the engine according to the value of current flowing between the electrodes 5 and 6 of the element 1. A target air/fuel ratio is set to control the air/fuel ratio of the supply mixed gas and when the target air/fuel ratio is below a specified value, the current supply to the element 1 is stopped by the circuit 11.

Description

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

BACKGROUND ART In order to purify the exhaust gas of internal combustion engines and improve fuel efficiency, an air-fuel system detects the oxygen concentration in the exhaust gas and feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine to a target air-fuel ratio according to the detection result. There is a fuel ratio control device.

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 degree of obscurity (Japanese Patent Laid-Open No. 153155/1983). Such an oxygen concentration detection device is provided with an oxygen cJ degree detector having a pair of flat oxygen ion conductive solid electrolyte materials.

The solid electrolyte material is arranged in the gas to be measured, and electrodes are formed on each of the front and back surfaces 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. has been done. One of the solid electrolytes acts as an oxygen pump element, and the other acts as a battery element for measuring oxygen concentration ratio. When J3 is in the gas to be measured and a current is supplied between the electrodes of the oxygen pump element so that the electrode on the gap side becomes the negative electrode, the oxygen gas in the gas in the gap is ionized on the negative electrode side of the oxygen pump element and becomes oxygen. It moves within the pump element toward the positive electrode surface and is released from the positive electrode surface as oxygen gas. At this time, due to the decrease in oxygen gas in the gap, a difference in oxygen concentration occurs between the gas in the gap and the gas outside the battery element, so a voltage is generated between the electrodes of the battery element, and the voltage is kept at a constant value. When the current value supplied to the oxygen pump element is changed in this manner, the current value becomes approximately proportional to the oxygen concentration in the gas to be measured at a constant temperature. Based on the current value supplied to the Mf pump element, it is determined whether the air-fuel ratio of the air-fuel mixture supplied to the engine is richer or leaner than the target air-fuel ratio. Air-fuel ratio controlled by secondary air
When t = J', if it is determined to be rich, secondary air is supplied to the engine, and if it is determined to be lean, then
By stopping the supply of secondary air, the air-fuel ratio is controlled to the target 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 dioxide) is used as the solid electrolyte material, oxygen 02 is taken away from Zr0z by excessive current supply to the oxygen pump element, and zirconium Zr is precipitated. This blackening phenomenon causes rapid deterioration of the oxygen pump element and deteriorates its performance as an oxygen concentration detector.

FIG. 1 shows the relationship between the oxygen concentration and the current value Ip 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.
The boundary line with the blackening phenomenon occurrence area is a linear function characteristic similar to the relationship characteristic using the voltage Vs as a parameter. In order to prevent the blackning phenomenon, the current supplied to the oxygen pump cord must be made smaller than the value in the blackening occurrence region.

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), the voltage Vs It was found that it moved violently up and down and became extremely unstable.

As a result, in order to control the voltage Vs to a constant value, the supply current value to the oxygen pump element also fluctuates, making it impossible to accurately determine the air-fuel ratio from the supply current value, and depending on the determination result, the air-fuel ratio of the supplied mixture is changed. Controlling this will result in poor drivability.

1 and View I Therefore, 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 close to the stoichiometric air-fuel ratio (=1).

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.

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

FIG. 2 shows an air-fuel ratio control device using an 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 lead lines 5a to 8a of the 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 element 1.
1, current is supplied. The current supply circuit 11 includes an operational amplifier 12. NPN transistor 13 and resistor 14.15
Consisting of The output end of the operational amplifier 12 is connected to the base of a transistor 13 via a resistor 14. Further, the emitter 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,
The terminal voltage is supplied to the Ip input terminal of the control circuit 31 as a pump current value 1p. The collector of the transistor 13 is connected to the inner electrode plate 6 of the oxygen pump cord 1 via a lead wire 6a, and a voltage v8 is supplied to the outer electrode plate 5 via the 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 inverting input terminal of the A bare amplifier 12 via a non-inverting amplifier 30 consisting of resistors 27 to 29. A D/A converter 32 is connected to the Ic control output terminal of the control circuit 31.
It generates a voltage according to the digital signal output from the Ic control output terminal of. The output terminal of the D/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.

The control circuit 31 is preferably composed of a microcomputer, and has an A/F drive end in addition to the above-mentioned Ic output end and Ip input end, and the A/F drive end is connected to a solenoid valve 44 for adjusting secondary air supply. It is connected.

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 this configuration, when a digital signal is output from the Ic output terminal of the control circuit 31 to the D/A converter 32, the D
The digital signal is converted into a voltage by the /A converter 32 and supplied to the voltage follower circuit 33. The output voltage of the voltage follower circuit 33 is supplied to the non-inverting input terminal of the operational amplifier 12 via the resistor 34 as the reference voltage Vr''+.At this time, the voltage level at the inverting input terminal of the operational amplifier 12 is lower than the reference voltage Vr+. Therefore, the output level of the operational amplifier 12 becomes high level, and the transistor 13 is turned on.By turning on the transistor 13, the oxygen pump element 1 is turned on.
A pump current flows between the electrode plates 5 and 6.

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 is supplied to the non-inverting amplifier 30 via the filter circuit 19.

The non-inverting amplifier 30 amplifies the output voltage of one filter circuit and supplies it to the inverting input terminal of the operational amplifier 12. When the voltage Vs increases, the output voltage Vs- of the non-inverting amplifier 30 increases.
will also rise. When the output voltage Vs- exceeds the reference voltage Vr+, the output level of the operational amplifier 12 is inverted to a low level, and the transistor 13 is turned off. Since the pump current decreases by turning off the transistor 13, the electrode plate 7 of the battery element 2
The generated voltage Vs between .degree. When the voltage V S - falls below the reference voltage Vr1, the output level of the operational amplifier 12 becomes high 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 corresponding to the value indicated by the digital control signal.

The pump current II flowing between the electrode plates 5.6 of the oxygen pump element 1 when supplying the reference voltage V r + to the operational amplifier 12
ρ is detected by the terminal voltage Vρ of the resistor 15, and the terminal voltage Vρ is supplied to the IP input terminal of the control circuit 31.

The control circuit 31 operates as follows in synchronization with engine rotation. As shown in FIG. 3, first, the control circuit 31 sets a target air-fuel ratio D 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 A/F D is set, for example, from the engine speed and the engine suction A/F tracheal pressure, and is retrieved from a data map stored in advance in a ROM or the like in the control circuit 31. After setting the target air-fuel ratio D, it is determined whether the target air-fuel ratio A/F DA/F is greater than a predetermined value 1)r (step 52). The predetermined 1lrJDr is a value slightly larger than the stoichiometric air-fuel ratio. If D ≦ [)r, then the target air-fuel ratio is set near the stoichiometric air-fuel ratio or richer than it, and the air-fuel ratio cannot be accurately determined from the pump current, so the supply of pump current is stopped. In order to set the reference voltage Vr+ to 0 [V], the content of the digital signal output from the Ic control output terminal is changed to °゛O'', for example, in the case of a 4-bit digital signal, to ``o o o o''. (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 transistors 1 to 13 are turned off, and the pump is applied between the electrode plates 5 and 6 of the oxygen pump element 1. No current flows. After executing step 53, the control circuit 31 stops driving the solenoid valve 440 to open in order to stop supplying secondary air to the engine (step 54), while DA/'F>[ ) r, then
Assuming that the target air-fuel ratio is set leaner than near the stoichiometric air-fuel ratio, the digital signal output from the Ic control output terminal is set to a predetermined oxygen concentration detection value in order to supply the pump current (step 55). After that, pump current value 1
The terminal voltage Vp is read as p (step 56), and it is determined whether the read pump current value Iρ is smaller than the reference current value 1r+ corresponding to the target air-fuel ratio DA7F (step 57). If Ip<Ir+, the air-fuel ratio of the air-fuel mixture supplied to the engine is rich, and the control circuit 31 opens the solenoid valve 44 to supply secondary air to the engine (step 58). If Ip≧Tr+, 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.

Note that in the embodiment of the present invention described above, when the target air-fuel ratio DA/F is smaller than the predetermined value Dr, the supply of pump current is stopped by changing the content of the digital signal, but the present invention is not limited to this. For example, the voltage at the non-inverting input terminal of the operational amplifier 12 may be forced to 0 (V). Further, if the target air-fuel ratio DA/F is retrieved from the memory in the control circuit 31 at the pump current level, the retrieved target air-fuel ratio DA/F is used as it is at the reference current value 1r.
It can be used as 1.

As described above, in the air-fuel ratio control device for an internal combustion engine of the present invention, when the target air-fuel ratio is set to a value near the stoichiometric air-fuel ratio at which the output of the oxygen concentration detection device becomes unstable, Since the current supply to the oxygen pump element is stopped, the blackening phenomenon can be avoided, and rapid deterioration of the oxygen pump element can be prevented. In addition, incorrect air-fuel ratio determination based on the pump current value is prevented. 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 the drawing]

Figure 1 is l! 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 operation of the control circuit in the device shown in FIG. 2. It is a flow diagram. 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 30...Non-inverting amplifier

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 which is arranged to face each other and 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 for changing the supplied current value so as to maintain the voltage generated between the electrodes of the battery element at a constant value; a discriminating means for discriminating the air-fuel ratio; and an air-fuel ratio adjusting means for setting a target air-fuel ratio of the air-fuel ratio of the supplied air-fuel mixture and adjusting the air-fuel ratio of the supplied air-fuel mixture to the target air-fuel ratio according to the determination result of the discriminating means. An air-fuel ratio control device, wherein the current supply means stops supplying current to the oxygen pump element when the target air-fuel ratio is below a predetermined value.