JPS6036946A - Control device for air-fuel ratio - Google Patents

Abstract

PURPOSE:To enable easy detection of whether an air-fuel ratio sensor attains activating temp. or not with a device for using the air-fuel ratio sensor of which the output changes proportionally to the air-fuel ratio and subjecting the gaseous mixture taken into an engine to feedback control by setting the reference voltage of an oxygen sensor at an adequate value after the start of the engine. CONSTITUTION:The analog value of the information on an intake air flow is converted to a digital value by an AD converter 20 while feedback control by an air-fuel ratio sensor 2 is not performed. A microprocessor 21 reads out the preprogrammed procedure and constant from an ROM 22 and operates an optimum fuel feed rate. The result of the arithmetic fed via an output interface circuit 24 to a means 15 for forming a gaseous mixture corresponds to the driving pulse width of, for example, an electromagnetic fuel injection valve provided in the means 15, by which the air-fuel ratio in the means 15 is controlled. The correction by pump current Ip is further added to the arithmetic of the open loop control in which the feedback control is not executed, in the operating state in which the feedback control is performed in accordance with the output from the sensor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a) a device for detecting an air-fuel ratio by measuring oxygen concentration in exhaust gas of an internal combustion engine, etc., and particularly relates to an oxygen pump type device constructed of an ion-conducting solid electrolyte. The present invention relates to a method for determining activation of an air-fuel ratio sensor in an air-fuel ratio control device using an air-fuel ratio sensor.

Conventionally, an oxygen sensor composed of an ion-conducting solid electrolyte (e.g. stabilized zirconia) is used to detect the stoichiometric air-fuel ratio by changing the electromotive force caused by the difference between the oxygen partial pressure of the exhaust gas and the oxygen partial pressure of the air. It is well known that, for example, an automobile engine can be controlled to operate at a stoichiometric air-fuel ratio by detecting the combustion state of the engine. By the way, the above oxygen sensor has an air-fuel ratio A/ which is the weight ratio of air and fuel.
When F is large at the stoichiometric air-fuel ratio of 14.7, a large change in output is obtained, but in other operating air-fuel ratios there is almost no change in output, and when the engine is operated at an air-fuel ratio other than the stoichiometric air-fuel ratio, The output of the oxygen sensor cannot be used.

This invention uses a solid electrolyte oxygen pump type oxygen concentration measuring device, which was proposed in Japanese Patent Laid-Open No. 130649/1983, which was said to be difficult to accurately detect the stoichiometric air-fuel ratio, to accurately detect the stoichiometric air-fuel ratio. The air-fuel ratio is controlled using an engine air-fuel ratio sensor that can detect not only the fuel ratio but also other air-fuel ratios. An embodiment of the present invention will be described below.

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure is a cross-sectional view taken along line ll-1 in FIG. In the figure, (
1) is an exhaust pipe of the engine, and (2) is an air-fuel ratio sensor disposed within the exhaust pipe (1). The air-fuel ratio sensor (2) has platinum electrodes (41
, (5), a solid electrolyte oxygen pump (G
), and a solid electrolyte oxygen sensor α [ which is constructed by providing platinum electrodes (8) and (9) on both sides of a flat ion-conducting solid electrolyte (7), which is the same as the oxygen pump (6). and the above oxygen pump (6).

It is composed of a support stand aυ for arranging the oxygen sensor rods facing each other with a minute gap 1111d of about 0.1 mm in between.

← 4 is the electronic control unit, and the above oxygen sensor scream is the electrode (
8) and (9) Apply the electromotive force e generated between them to the inverting input terminal of the operational amplifier via the resistor Rz, and apply the reference voltage Vs applied to the non-inverting input terminal of the operational amplifier A.
The output of the operational amplifier A proportional to the difference between the electromotive force e and the electromotive force e drives the transistor TR to
6) has a function of controlling the pump current IP flowing between the electrodes (4) and (5). That is, it functions to supply the pump current I'P necessary to maintain the electromotive force e at a predetermined value (Vs).

Further, a resistor RO is provided for obtaining an output signal corresponding to the pump current IP supplied from the DC power supply B serving as pump current supply means. This resistor no corresponds to the DC power supply B, and a desired resistance value is selected so that the pump current IP does not flow excessively. C is a capacitor, and S is a switching device for changing the reference voltage Vs from Ml to Vs.

FIG. 3 shows the results of a test in which the air-fuel ratio sensor of the present invention constructed as described above was installed in a gasoline engine of a domestic passenger car 2000. If an excessive pump current IP flows, the oxygen pump <6) will be destroyed, so the pump current I
P was limited by the DC power source B so that it did not flow more than 100 mA. In addition, as a result of testing with the reference voltage (8) set to V 1 = 55 mV and (2) set to 200 mV, the characteristic of (a) shown in Figure 3 is obtained by the switching device S). Obtained. Further, the switching device S sets the reference voltage VB to VB=200.
When the voltage was changed to mV, the characteristics shown in (b) were obtained. If you try to detect the air-fuel ratio A/F in a wide range of 12 to 19 using the above characteristics, in the characteristic 6), there are two air-fuel ratio points with the same pump current value, so it can be detected only with the above pump current value. Can not do it. On the other hand, in the characteristic (b), since there is no change in the pump current IP in the range of the stoichiometric air-fuel ratio of 14.7 or less, the air-fuel ratio cannot be detected in this range. Therefore, for example, when detecting the air-fuel ratio during engine operation, first,
The switching device S sets the reference voltage Vs to Vz. Then, according to the characteristic '(b) above, when the operating air-fuel ratio is smaller than the stoichiometric air-fuel ratio, the pump current IP is 10.
If it is 0mA, if it is larger than the stoichiometric air-fuel ratio, it will be smaller than 100mA, so the above operating air-fuel ratio is the stoichiometric air-fuel ratio)
It can detect whether it is small or large. Next, the switching device S changes the reference voltage (8) to Vz, and the above (a)
Depending on the characteristics of the air-fuel ratio, the operating air-fuel ratio can be detected in a range smaller or larger than the stoichiometric air-fuel ratio.

The reason why the pump current IP changes in proportion to the air-fuel ratio in a range where the air-fuel ratio A/F is larger than the stoichiometric air-fuel ratio, as shown by the characteristics in FIG. 3, is described in JP-A-56-130649. has been done. That is, by changing the oxygen partial pressure of the exhaust gas introduced into the micro-' sparse part d by the action of the oxygen pump (6), the oxygen content of the exhaust gas flowing inside the exhaust pipe (1) can be reduced. #f! of the oxygen sensor +1I11 generated in response to the difference in oxygen partial pressure. , 9-h
p-AtTit 9i? When controlling the pump current IP supplied to the pump (6), this pump current IP changes in proportion to the oxygen concentration in the exhaust gas. Since the air-fuel ratio is approximately proportional to the oxygen concentration, the pump current IP changes in proportion to the air-fuel ratio A/F. Incidentally, the reason why the pump current Np changes in a range smaller than the stoichiometric air-fuel ratio is considered to be because the air-fuel ratio sensor (2) is sensitive to the carbon monoxide (CO) concentration in the exhaust gas.

As described above, the air-fuel ratio can be controlled to the stoichiometric air-fuel ratio and the air-fuel ratio other than the stoichiometric air-fuel ratio using the solid electrolyte oxygen sensor Q (1) and the oxygen pump (6). 2) can exhibit the characteristics shown in Fig. 3 only when the temperature of the air-fuel ratio sensor (2) is above a predetermined value (for example, 500°C), and when the temperature is low, the characteristics shown in Fig. 4 can be exhibited. The characteristics deteriorate as shown by the broken lines ag and ba, and it becomes impossible to know the accurate air-fuel ratio (A/F).

This invention prevents the problem that if the proportional output range of the air-fuel ratio sensor is used when the engine temperature is low after the engine has started, the air-fuel ratio detection accuracy will be low and the error will be large. is the pump current (I) of the air-fuel ratio sensor (2)
P) Set the reference voltage (v8) so that the output characteristics switch inverted at the stoichiometric air-fuel ratio point, monitor the pump current (IF) value while the engine is running, and set the air-fuel ratio sensor (2)
This is to determine the activation of. Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1, a3 is a current-voltage converter that converts the pump current (Ip) into a voltage level, α4 is a control device that receives a signal from this converter α4, and also sends a signal to the air-fuel mixture generating means (1ω); 161 is an internal combustion engine, (Iη is a key switch that is closed when the vehicle is running. The main character is an AD converter that converts the analog output of the current-voltage converter and intake air amount information into digital values, and Qυ ROM (2) is a microprocessor that performs arithmetic and logical processing according to the procedure of a program written in advance; (c) is a microprocessor (2) that temporarily stores the calculated values (RAM);
In response to the results of the arithmetic and logical processing of the microprocessor (2υ), the switching device (3) in the electronic control unit a2 is switched to V.
Signal to switch to x or Vz and mixture generation means (to)
The control device α41 is composed of an output interface circuit that outputs an electric signal for controlling the amount of fuel supplied or the amount of intake air to the engine.

The operation of one embodiment configured in this way will be explained. First, in operating conditions where feedback control by the air-fuel ratio sensor (2) is not performed, the analog value of the intake air amount information is converted to a digital value by the AD converter (2), and the analog value of the intake air amount information is converted to a digital value by the microprocessor (2) The optimum fuel supply amount is calculated by reading the pre-programmed procedure and constants.The calculation result is sent to the air-fuel mixture generating means α9 via the output interface circuit. For example, it corresponds to the driving pulse width of an electromagnetic fuel injection valve, and the mixture generating means (
The air-fuel ratio at 15 is controlled. Next, the output of the air-fuel ratio sensor (2) tb pump current CI? ), a correction based on the pump current (Ip) K is added to the feed calculation described above, but this correction generally includes a moderate amount of ripple due to PI control. .

Incidentally, in the present invention, activation determination of the air-fuel ratio sensor (2) is performed in the following procedure. That is, when the key switch aη is turned on when the vehicle starts driving, the fifth
As shown in the flowchart of the figure, the changeover switch (S) in the electronic control device α4 is set to the reference voltage Vs=Vz by the output of the control device α4. Reference voltage VB=V
When the temperature of the air-fuel ratio sensor (2) is above a predetermined value, it exhibits the characteristics shown in bx in Fig. 4, but when the temperature is not high enough, it exhibits output characteristics at a lower level, such as bs or hiro. show. While the engine is warming up after starting, the air-fuel ratio sensor (
2) Because the temperature is low, sufficient output characteristics cannot be obtained, and the fuel current (IF) is low in the rich air-fuel ratio region.
Since the reference voltage (Vs) does not reach I, the reference voltage (Vs) remains set at ■1, but when the temperature rises and the pump current (IF) exceeds IPl, the air-fuel ratio sensor (2) activates the shi 1 house I 舅Iviewraiza rVg) 糾Vnegativef stirrup h-
The regular characteristic al shown in FIG. 4 can be used.

In addition, as a method for determining activation of the air-fuel ratio sensor (2), a reference voltage (v8) was set so that the characteristic of the air-fuel ratio sensor (2) reverses switching at the stoichiometric air-fuel ratio point. If the reference voltage (Vs) is set so that (2) obtains a proportional output to the air-fuel ratio, it is difficult to distinguish whether the output decreases due to temperature or the output pump current (IP) or the output decreases due to the actual air-fuel ratio. Because you can't.

As described above, according to the present invention, in a device that feedback-controls the air-fuel mixture taken into an engine using an air-fuel ratio sensor whose output changes proportionally to the air-fuel ratio, the oxygen sensor By setting the reference voltage to an appropriate value, it is possible to very easily detect whether or not the air-fuel ratio sensor has reached its activation temperature.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an embodiment of the present invention; Fig. 2 is a sectional view showing the air-fuel ratio sensor of Fig. 1; Figs. 3 and 4;
The figure is a characteristic diagram of the air-fuel ratio sensor, and FIG. 5 is a flowchart showing the operating procedure of an embodiment of the present invention. (2)・e-・Air-fuel ratio sensor, (121...Electronic control unit, α1...-Current voltage converter, a4...Adjustment control device. Agent: Masuo Oiwa, Figure 1) Figure 2 3 Diagram □ 14/F) Roku Seki

Claims (1)

[Claims] A gap section into which engine exhaust gas is introduced, a solid electrolyte oxygen pump that controls the oxygen partial pressure within this gap section, and an actuator corresponding to the oxygen partial pressure within the gap section and the fluorine partial pressure in the exhaust gas outside the gap section. An air-fuel ratio sensor equipped with a solid electrolyte oxygen sensor that generates electric power, and an output signal corresponding to the pump current of the oxygen pump necessary to maintain the electromotive force generated by the oxygen sensor of this air-fuel ratio sensor at a predetermined value. In an air-fuel ratio control device comprising a control device configured to detect the air-fuel ratio of the engine, and an air-fuel mixture generating means that is feedback-controlled in accordance with the output signal of the air-fuel ratio sensor, the oxygen pump is activated when the engine is started. The electromotive force of the oxygen sensor is set so that the pump current changes rapidly at the stoichiometric air-fuel ratio, and after the pump current reaches a predetermined level or higher during engine operation, the pump current of the oxygen pump changes rapidly relative to the air-fuel ratio. An air-fuel ratio control device characterized in that the electromotive force of an oxygen sensor is set so as to change proportionally.