JPS5934432A - Air-fuel ratio controller of internal-combustion engine - Google Patents

Abstract

PURPOSE:To enable to perform reliable control of an air-fuel ratio to a desired value irrespective of the individual difference of a lean sensor, by installing a lean sensor output characteristic correcting means which corrects the output signal of the lean sensor to a reference characteristic depending on the individual difference of the lean sensor. CONSTITUTION:According to an exhaust air-fuel ratio being found from the output of a lean sensor 28, feedback correction and the like is applied to the basic injection quantity to determine a practical injection amount, and an electronic controller 32 outputting a valve opening time signal to an injector 22 is provided. The electronic controller 32 is provided with a non-inversion amplifier 70 having variable amplification factor, which amplifies the output of the lean sensor 28 inputted through a current-voltage converter 46, and a lean sensor output characteristic correcting means consisting a potentiometer dial 72 for correcting an output characteristic, matching the individual difference of the lean sensor 28, to a reference signal through adjustment of the amplification factor of the non-inversion amplifier 70 by changing the resistance value of a variable resistor R2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an internal combustion engine, and in particular, to an air-fuel ratio control device for an exhaust gas in an air-fuel ratio range suitable for use in an automobile engine equipped with an electronically controlled fuel injection device. , a lean sensor that generates an output signal substantially proportional to the oxygen concentration in the exhaust gas, an intake air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied into the engine combustion chamber, and a lean sensor that generates an output signal that is approximately proportional to the oxygen concentration in the exhaust gas; The present invention relates to an air-fuel ratio control device for an internal combustion engine, including an electronic control device that performs feedback control of the intake air-fuel ratio control means so that the air-fuel ratio becomes a target value in accordance with an exhaust air-fuel ratio.

In internal combustion engines, especially automatic military engines that use three-way catalysts to purify exhaust gas, the air-fuel ratio of the exhaust gas (referred to as the exhaust air-fuel ratio) must be kept strictly close to the stoichiometric air-fuel ratio. Therefore, for example, the air-fuel ratio of the air-fuel mixture supplied into the engine combustion chamber is controlled by using an oxygen concentration sensor that detects the air-fuel ratio from the oxygen concentration in the exhaust gas and by controlling the fuel injection amount. An intake air-fuel ratio control means consisting of an electronically controlled fuel injection device, and a fuel injection amount of the electronically controlled fuel injection device so that the air-fuel ratio becomes near the stoichiometric air-fuel ratio according to the JJ air-fuel ratio determined from the oxygen concentration output. An air-fuel ratio control device having an electronic control device that performs feedback control has been put into practical use.

According to such an air-fuel ratio control device, the air-fuel ratio can be feedback-controlled so as to be close to the stoichiometric air-fuel ratio, and therefore the exhaust gas purification performance of the three-way catalyst arranged in the exhaust system can be sufficiently controlled. However, although the above-mentioned advanced air-fuel ratio control device can improve exhaust gas purification performance, it always controls the air-fuel ratio to be close to the stoichiometric air-fuel ratio. Even in operating conditions where the air-fuel ratio is acceptable for regular use, we investigated the cases in which the air-fuel ratio is increased and the fuel efficiency is not sufficiently improved.

In order to eliminate the above-mentioned drawbacks, attempts are being made to improve the fuel efficiency of the engine by setting the air-fuel ratio to a leaner side than the stoichiometric air-fuel ratio, so-called lean combustion. In the exhaust gas lean air-fuel ratio range, there is a good correlation between the oxygen concentration in the exhaust gas and the air-fuel ratio. One type of sensor that measures exhaust oxygen concentration (referred to as a lean sensor) is a gas permeability measurement electrode into which the exhaust gas to be measured can be introduced, and a reference gas (e.g., atmospheric air) with a known oxygen concentration. There is a sensor with a bottomed cylindrical element consisting of an air-permeable counter electrode that can be introduced and a solid electrolyte (for example, stabilized zirconia) between the two electrodes. In this sensor, when a current is passed between the two electrodes, oxygen is released through the electrolyte. Although it can be moved in one direction, it can be moved within a certain applied voltage range by covering the air permeability measuring electrode with a microporous diffusion resistance layer that introduces a smaller amount of oxygen than the oxygen delivery capacity of the air permeability measuring electrode. Then, the current value can be maintained at a constant value.

This constant current value is the limit current value! So, this work! changes almost linearly in proportion to the oxygen concentration, so the limiting current value is Oxygen concentration can be continuously detected from changes in .

Generally, when this type of lean sensor is used for exhaust air-fuel ratio feedback control of an internal combustion engine, 90
The air-fuel ratio output must always be stable even in a high-temperature atmosphere of about 0°C.

Therefore, the material of the diffusion resistance layer of the lean sensor element is a heat-resistant porous ceramic material such as spinel or alumina. Plasma spray manufacturing method is used to coat the ceramic material. By the way, in order to fully produce lean sensors and use them in internal combustion engines, etc., the diffusion current value must be determined by individual differences under a constant atmosphere. (It is necessary to output a constant value. For this purpose, in manufacturing the sensor, the micropore structure (e.g., pore diameter, porosity, thickness, etc.) of the diffusion resistance layer must always be kept constant. However, in order to maintain a constant micropore structure using the plasma spray manufacturing method, there is a limit even if the manufacturing control is performed with high precision and frequency, and as a result, the lean sensor Therefore, if air-fuel ratio feedback control is performed based on the lean sensor output signal, which has individual differences, it will not be possible to accurately control the target air-fuel ratio (and the lean sensor output signal will not match the standard). If the lean sensor output signal is larger than the standard characteristic, the air-fuel ratio will be controlled to be leaner than the target air-fuel ratio, resulting in deterioration of engine operating performance and fuel efficiency.On the other hand, if the lean sensor output signal is larger than the standard characteristic, the air-fuel ratio will be controlled to be leaner than the target air-fuel ratio. There was a risk that fuel efficiency would deteriorate and the concentration of harmful components in exhaust gas would increase.

The present invention aims to eliminate the above-mentioned drawbacks of the conventional technology, and is an air-fuel ratio control for an internal combustion engine that can easily and accurately control the fuel ratio to a target value regardless of individual differences in lean sensors. The purpose is to provide equipment.

The present invention provides a lean sensor that generates an output signal that is approximately proportional to the oxygen concentration in the exhaust gas in the exhaust gas No. 1 air-fuel ratio range, and a lean sensor that generates an output signal that is approximately proportional to the oxygen concentration in the exhaust gas, and a lean sensor for controlling the air-fuel ratio of the air-fuel mixture supplied into the engine combustion chamber. An air-fuel ratio of an internal combustion engine comprising an intake air-fuel ratio control means and an electronic control device that performs feedback control of the intake air-fuel ratio control means so that the air-fuel ratio becomes a target value according to an exhaust air-fuel ratio determined from the output of the lean sensor. In the control device, the above object is achieved by providing the electronic control device with a lean sensor output characteristic calibrating means for calibrating the lean sensor output signal to a reference characteristic according to individual differences of the IJ-sensor. .

Further, the individual differences in the lean sensors are determined by comparing the lean sensor output value under atmospheric oxygen concentration with a reference value, so that the individual differences in the lean sensors can be easily and accurately determined. 7j thing.

Furthermore, the lean sensor output characteristic calibrating means includes an amplifier with a variable amplification rate provided in the electronic control unit for amplifying the output signal of the lean sensor, and an amplifier externally attached to the electronic control unit. It consists of a potentiometer dial for calibrating the output characteristics of the lean sensor by adjusting the amplification factor of the amplifier.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In this embodiment, as shown in FIG. 1, an accelerator pedal ( (not shown); a surge tank 16 for preventing intake interference; and a precise intake pipe pressure for detecting intake pipe pressure from the pressure inside the surge tank 16. The sensor 18 and the engine 1 disposed in the intake manifold 20
An injector 22 for injecting fuel by turning to the intake port 0, a spark plug 24 for igniting the air-fuel mixture introduced into the engine combustion chamber 10a, and an exhaust gas disposed in an exhaust manifold 26. A lean sensor 28 generates an output signal that is approximately proportional to the oxygen concentration in the exhaust gas in the air-fuel ratio range of 1000 yen, and the engine rotational speed is determined based on the rotation of the detripulator shaft, which is built in, for example, the detripulator (not shown). The rotation speed unit that outputs the signal determines the actual injection amount by adding feedback correction, etc. according to the exhaust air-fuel ratio obtained from the output of the lean sensor 28 to the basic injection amount obtained from the map according to the engine rotation speed obtained. , and an electronic control device 32 that outputs a valve opening time signal to the injector 22.
In the intake pipe pressure sensing type electronically controlled fuel injection device of 0,
The electronic control device 32 is provided with lean sensor output characteristic calibrating means for calibrating the lean sensor output signal to a reference signal in accordance with individual differences in the lean sensor 28.

As shown in detail in FIG. 2, the lean sensor 28 includes a bottomed cylindrical element body 28a made of a stabilized zirconia solid electrolyte with oxygen ion conductivity, and a notch on the outer surface of the element body 28a. , an air permeability measuring electrode (cathode) 28b into which the gas to be measured can be introduced, and a known oxygen concentration (approximately 21%).
Air permeable counter electrode (anode) 28C that can introduce atmosphere with
, a porous ceramic diffusion resistance layer 28d provided to cover the cathode 28b, a heater 28e disposed in the center so that its tip approaches the bottom of the element body 28a, and a heater 28e for protecting the element assembly. Gas flow hole 28 to be measured
It is composed of a louver 28f having a diameter of 1.g, and a flange 28h for attaching the element assembly to the exhaust pipe of the engine.

Here, the cathode 28b and the anode 28c are made of a heat-resistant electron conductor such as platinum, and a diffusion resistor 1628a is used.
is made of a heat-resistant inorganic material such as alumina, magnesia, spinel, etc., and has the function of restricting the flow of oxygen into the cathode 28b. Lean sensor 28 with such a configuration
When a DC voltage is applied between the positive and negative poles by attaching it to the exhaust pipe of an engine and bringing it into contact with the exhaust gas, or by attaching it to a heating furnace into which atmospheric air is introduced, and applying a DC voltage between the positive and negative poles, the Only a current of 1 flows, which causes so-called limiting current characteristics. Figure 3 is a diagram showing the correlation between the limiting current value at -voltage in the voltage range that produces this limiting current characteristic, oxygen 1a in the exhaust gas, and atmospheric oxygen concentration (approximately 21%). It is.

From Figure 3, it is shown that the limiting current value increases linearly as the oxygen concentration increases, and from this, if the limiting current value is determined, the oxygen concentration in the exhaust gas, and therefore the air-fuel ratio, can be detected. is clear. Further, solid lines A and B%C in FIG. 3 indicate the correlation between the limiting current value and the oxygen concentration due to individual differences in lean sensors. The lean sensor with a high output limit current value ai, which is the standard at atmospheric oxygen concentration, is shown by solid line A, and the lean sensors shown by solid lines B and C have individual limit current values (a) and (c) at that atmospheric oxygen concentration, respectively. By multiplying the value by a value of 0, it is possible to calibrate to the reference lean sensor output value (solid line A) even under any oxygen concentration. Figure 4 is a diagram showing the correlation, and the vertical axis shows the limit current value of the lean sensor at atmospheric oxygen concentration on the sleeve, and the limit current value a of the reference lean sensor on the vertical axis. This shows the calibration value. Here, the limiting current value of each lean sensor at atmospheric oxygen concentration can be measured, for example, by placing the lean sensor in a heating furnace into which air is introduced.

As shown in detail in FIG. 5, the electronic control unit 32 is connected to a 7th central processing unit (referred to as M P, U) 40 which performs various arithmetic processing, for example, a microprocessor, and a buffer 42 . The input signal is input via an analog-to-digital converter (referred to as an A/D converter) 44 for converting the intake pipe pressure signal output from the intake pipe pressure sensor 18 into a digital signal, and a current-voltage converter 46. An A/D converter 48 for converting the air-fuel ratio signal output from the lean sensor 28 into a digital signal; an input board 52 for taking in rotational speed signals, a read-only memory (referred to as ROM) 54 for storing control programs and various constants, and a random memory for temporarily storing calculation data, etc. in the MPU 40. an access memory (referred to as RAM) 56, a clock generation circuit 58 for generating various clock signals, an output port 0 for outputting data for operating the injector 22 according to the calculation results in the MPU 40; According to the data output from the output port 0, the output port 0 also counts down the sent data to the clock generation circuit 5.
Starts with the clock signal of 8 outputs, and the count value is 0.
a down counter 62 that completes counting and generates a count completion signal at an output terminal when the clock signal reaches the clock signal, and an S-R flip-flop 64 that is reset by the output of the down counter 62 and set by the output of the clock generation circuit 58; a power amplifier 6 for energizing the injector 22 while the down counter 62 is counting down according to the output of the S-R flip-flop 64;
6, and the current-voltage converter 4 in this electronic control device 32.
6 and the A/D converter 48, and includes a fixed resistor R2 and a variable resistor I6 for amplifying the output of the lean sensor 28 that is input via the current-voltage converter 46. The amplification factor of the non-inverting amplifier 70 is adjusted by changing the resistance value of the non-inverting amplifier 70 with a variable ratio and the variable resistor R2 externally connected to this electronic control device 32. It is comprised of a lean sensor output characteristic calibrating means such as a potentiometer dial 72 for calibrating the output characteristics, and a bidirectional bus 74 for connecting the respective component devices.

The ROM 54 stores in advance the relationship shown by the solid line A of the reference lean sensor shown in FIG. 3 above, but in this case, the vertical axis in FIG.
In the ROM 54, the relationship between the voltage V and the oxygen concentration P shown by the solid line A in FIG. 3 is stored in the form of a data table or function.

The action will be explained below.

In this embodiment, by first operating the potentiometer dial 72 in accordance with the output characteristics of the lean sensor 28, the output characteristics of the lean sensor 28 are adjusted to the standard lean shown by the solid line A in FIG. Match the output characteristics (standard characteristics) of the sensor. Specifically, for example, the potentiometer dial 72 is rotated in response to a deviation in the output voltage of the lean sensor 28 with respect to the output voltage of the reference lean sensor, which is measured by a lean sensor tester consisting of a heating furnace into which atmospheric air is introduced. However, by changing the amplification factor of the output voltage of the lean sensor 28, the output characteristics of the lean sensor 28 are made to match the output characteristics of the reference lean sensor.

Air-fuel ratio feedback control by the lean sensor 28 whose output characteristics have been calibrated in this manner is executed according to a time interrupt routine as shown in FIG. That is,
First, in step 101, depending on the engine operating range determined from the engine rotational speed output from the degree sensor 30,
A target air-fuel ratio (for example, a lean air-fuel ratio) stored in the ROM 54 in advance is set. Next, the process proceeds to step 102, where the target output voltage value V of the lean sensor 28 is determined from the relationship shown by the solid line A in FIG. Calculate. Then,
Proceeding to step 103, the basic injection time τ is determined.

Calculate it. Furthermore, the process proceeds to step 104, where the current output voltage value V of the lean sensor 28 is the target output voltage value V. It is determined whether or not the value is greater than or equal to the value. If the determination result is positive, the process proceeds to step 105, where the result of adding a partial value α to the current air-fuel ratio feedback correction coefficient f is calculated as a new air-fuel ratio feedback correction coefficient f, as shown in the following equation. do.

f+-f+α ・・・・・・・・・・・・・・・・・・
(1) On the other hand, if the judgment result in step 104 is negative, the process proceeds to step 106, and the result of subtracting the current air-fuel ratio feedback correction coefficient f or the partial value β is calculated as shown in the following equation. Let it be a new air-fuel ratio feedback correction coefficient j''.

f(, −f−β・・・・・・・・・・・・・(2
) After completing Stesono 106 or 105, step 107
Then, the basic injection time τ obtained in step 103 is determined. As shown in the following equation, the effective injection time τ is determined by multiplying by the air-fuel ratio feedback correction coefficient f,
End this time interrupt routine.

τ-f・τ.・・・・・・・・・・・・・・・・・・(
3) According to the execution injection time τ determined in step 107 of this time interrupt routine, a valve opening time signal corresponding to the execution injection time τ is output to the injector 22, for example, by the crank angle interrupt routine, and the fuel is injected into the injector 22. It is injected from 22.

FIG. 7 shows an example of the relationship between the output voltage of the lean sensor 28 and the air-fuel ratio feedback correction coefficient in this embodiment.

As shown in FIG. 7, the output voltage value V of the lean sensor 28
is the target output voltage value V. When the air-fuel ratio becomes larger than the target air-fuel ratio (then the air-fuel ratio feedback correction coefficient f is increased by α, the fuel injection amount increases and becomes thicker, and on the other hand, the output voltage V Target voltage value V
. When it becomes smaller than , the air-fuel ratio feedback correction coefficient f is decreased by β, and the fuel injection amount is decreased. That is, the air-fuel ratio can be accurately controlled to the target air-fuel ratio by comparing the output voltage value of the lean sensor 28 with the target output voltage value and performing feedback control on the fuel injection amount based on the determination result.

In the above embodiment, the present invention was applied to an automobile engine equipped with an electronically controlled fuel injection device that senses intake pipe pressure, but the scope of application of the present invention is not limited to this.
The intake air-fuel ratio can be adjusted by controlling the effective area of the fuel passage or air bleed passage for forming an air-fuel mixture by using an automobile engine equipped with an electronically controlled fuel injection device that senses the amount of intake air, or an air-fuel ratio control means. It is obvious that by using a control solenoid valve that controls the control, it can be similarly applied to a general internal combustion gradual opening system that does not have an electronically controlled fuel injection device.

As described above, according to the present invention, individual differences in lean sensors can be easily absorbed, and the air-fuel ratio can be accurately controlled to a target value regardless of individual differences in lean sensors. Therefore, the accuracy of air-fuel ratio control can be greatly improved, and in particular, in a lean combustion system, control at a lean air-fuel ratio that is very close to the lean limit is possible, and fuel efficiency can be greatly improved. It has an excellent effect of reducing harmful components in air gas.

[Brief explanation of the drawing]

FIG. 1 shows the air-fuel ratio fIII of the internal combustion engine according to the present invention.
FIG. 2 is a cross-sectional view showing the structure of the lean sensor used in the embodiment, and FIG. FIG. 4 is a diagram showing an example of the sensor output %1 raw, and FIG. FIG. 5 is a block diagram showing the configuration of the electronic control device including the lean sensor river force characteristic calibration means used in the above (19) embodiment, and FIG. FIG. 7 is a flowchart showing a time interrupt routine for feedback controlling the air-fuel ratio. 10... Engine, 18... Intake pipe pressure sensor, 22
...Injector, 28...Lean sensor, 30.
...Rotational speed sensor, 32...Electronic control device, 40.
...Central processing unit, 46...Current voltage converter, 48.
...Analog-digital converter, 52...Input port, 54...Read-only memory, 56...Random access memory, 58...Clock generator, 60...
...Output boat, 62...Down counter, 64...
・S-R flip-flop, 66...Power amplifier, 70
. . . Non-inverting amplifier, 72 . . . Potentiometer dial, 74 . . . Bidirectional bus. Agent Takaya Ron (and 1 other person) (20) Figure 6-177- Figure 7

Claims (3)

[Claims] (1) A lean sensor that generates an output signal that is approximately proportional to the oxygen concentration in the exhaust gas in the exhaust gas No. 1 air-fuel ratio range, and an intake sensor that controls the air-fuel ratio of the air-fuel mixture supplied into the engine combustion chamber. Air-fuel ratio control for an internal combustion engine, comprising: an air-fuel ratio control means; and an electronic control device that performs feedback control of the intake air-fuel ratio control means so that the air-fuel ratio reaches a target value according to the exhaust air-fuel ratio determined from the lean sensor output. Air-fuel ratio control for an internal combustion engine, wherein the electronic control device is provided with lean sensor output characteristic calibration means for calibrating the lean sensor output signal to a reference characteristic according to individual differences in the lean sensor. Device. (2) The air-fuel ratio control for an internal combustion engine according to claim 1, wherein the individual difference of the lean sensor is determined by comparing the lean sensor output value under atmospheric oxygen concentration with a reference value. Device. (3) The lean sensor output characteristic calibrating means includes an amplifier with a variable amplification rate provided in the electronic control device for amplifying the output signal of the lean sensor, and an amplifier externally attached to the electronic control device. The air-fuel ratio control device for an internal combustion engine according to claim 1, further comprising a potentiometer dial for calibrating the output characteristics of the lean sensor by adjusting the amplification factor t'' of the amplifier.