JPS6296743A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To keep drivability in an optimum state in despite of a variation in alcohol content, by making the detected value of an oxygen content detecting device compensable to the value corresponding to an actual equivalence ratio according to the alcohol content, in case of an engine using alcohol-blended fuel. CONSTITUTION:In case of a device which feeds an internal combustion engine M1 with blended fuel blending alcohol with other fuel by a fuel feeding device M2, in the state that a bias voltage is impressed, there is provided with an oxygen content detecting device M4 which detects oxygen content in an engine exhaust system M3. Then, on the basis of the detected value of this detecting device M4, the fuel feeding device M2 is controlled and an equivalence ratio (the ratio of a theoretical air-fuel ratio in the internal combustion engine M1 to an actual air-fuel ratio) is adjusted to the specified equivalence ratio. In addition, on the basis of alcohol content in the alcohol-blended fuel to be fed by the fuel feeding device M2, the bias voltage of the oxygen content detecting device M4 is made so as to be compensated by an alcohol content compensating device M6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to an air-fuel ratio control device for an internal combustion engine that uses alcohol mixed fuel as fuel.

[Prior Art] There is a technique disclosed in Japanese Unexamined Patent Publication No. 56-98540 for operating an internal combustion engine using conventional alcohol mixed fuel in an optimal state. This technology detects the mixing ratio of alcohol mixed fuel, determines the optimum amount of fuel at that mixing ratio using a map, etc., and supplies the fuel.

[Problems to be Solved by the Invention]However, in order to further improve fuel efficiency, an attempt was made to perform air-fuel ratio feedback control using a lean mixture sensor that produces an output corresponding to a lean air-fuel ratio as shown in Figure 13. . However, the following new problems were discovered. In other words, as shown in Fig. 14, the lean mixture sensor described above exhibits an output current characteristic proportional to the oxygen concentration for gasoline, but when the gasoline is changed to methanol, the output current increases in the region where the oxygen concentration is low. This shows that. On the other hand, when the bias voltage is changed and the methanol output characteristic is set to be proportional as shown in FIG. 15, the output current for gasoline exhibits a characteristic that the output current becomes small in the high oxygen Ila region.

Therefore, when air-fuel ratio feedback control is performed on a fuel mixture of methanol and gasoline using the lean mixture sensor, the output current of the lean mixture sensor, which is the reference for the feedback control, changes depending on the mixing state of methanol. There is a problem in that the air-fuel ratio control fluctuates.

Therefore, it is an object of the present invention to solve the above problems and perform appropriate air-fuel ratio control.

[Means for solving the problem] As a means to solve the above problem and achieve the purpose, as shown in Fig. 1, alcohol mixed fuel, which is a mixture of alcohol and other fuel, is supplied to the internal combustion engine M1. fuel supply means M2; and oxygen concentration detection means M4 for detecting the oxygen concentration in the exhaust system M3 of the internal combustion engine M1 while a bias voltage is applied.
and controlling the fuel supply means M2 based on the detected value of the oxygen concentration detection means M4 to make the equivalence ratio, which is the ratio between the stoichiometric air-fuel ratio and the actual air-fuel ratio of the internal combustion engine M1, to a predetermined equivalence ratio. an air-fuel ratio 11111 of an internal combustion engine comprising means M5;
The apparatus is characterized by further comprising: alcohol concentration correction means M6 for correcting the bias voltage of the oxygen concentration detection means M4 based on the alcohol concentration of the alcohol mixed fuel supplied by the fuel supply means M2. The main topic is air-fuel ratio control devices for internal combustion engines.

Other fuels in the alcohol mixed fuel supplied to the internal combustion engine M1 include, for example, gasoline, isopentane,
Or isobutane etc.

The fuel supply means M2 is, for example, a carburetor or a fuel injection device.

For example, as shown in FIG. 2, the oxygen concentration detection means M4 means that when a bias voltage (■) is applied to the zirconia solid electrolyte ZS under a predetermined temperature condition or higher and a current (■) is forced to flow, oxygen ions are detected through the solid electrolyte partition wall. This is a lean mixture sensor that detects the oxygen concentration in exhaust gas by utilizing the principle of movement of oxygen. The lean mixture sensor is a third
As shown in the figure, as the oxygen concentration increases from A% to 4A%, the output current increases, and as the bias voltage increases, the output current saturates and becomes constant. The structure when actually used as a detection element is as shown in FIG. In this structure, the lean mixture sensor part shown in Fig. 2 is covered with a protective cover and exposed to exhaust gas, and the reflective surface of this exposed part is opened to the atmosphere and a heater is installed in that part. It is something that

The control means M5 is composed of, for example, a microcomputer, and controls the fuel supply means M2 in a direction in which the output current of the oxygen concentration detection means M4 reaches a predetermined value corresponding to a predetermined equivalence ratio.
The amount of fuel supplied is controlled by controlling the amount of fuel supplied. The above equivalence ratio is equivalent ratio-stoichiometric air-fuel ratio/actual air-fuel ratio.

The alcohol concentration correction means M6 applies, for example, a bias voltage corresponding to the alcohol concentration of the alcohol mixed fuel supplied by the fuel supply means M2 to the lean mixture sensor, which is the oxygen concentration detection means. The bias voltage can be set using a switch if the alcohol concentration is known, or can be set using a detected value using an alcohol concentration sensor that detects the alcohol concentration based on changes in the dielectric constant of the fuel if it is unknown. This alcohol concentration sensor may be provided anywhere between the fuel tank and the injection valve, but the closer it is to the injection valve, the better it can respond to cases where the alcohol concentration changes midway.

[Operation] When gasoline is used in the lean mixture sensor, which is an example of the oxygen concentration detecting means M4 having the above configuration, the characteristics of the bias voltage and the output current are curved as shown by the dotted line in FIG. This characteristic has a flat saturation region in the middle of the bias voltage, and shows a characteristic that the higher the oxygen 1lIIlf, the larger the output current in the GM (lean air-fuel ratio) curve than in the Gr (rich air-fuel ratio) curve. The middle of the saturation region is the bias voltage (2) 9 in the figure, and when the oxygen concentration is detected at this Vg, a characteristic that slopes upward to the right as shown by the dotted line in FIG. 6 is obtained.

On the other hand, the results of measurement using alcohol are the M curve and the Mr curve shown by solid lines in FIG.

The middle of the saturation region of the curve is the bias voltage Vm in the figure, and when the oxygen concentration is detected at this Vll, the same upward-sloping characteristic as for gasoline is obtained, as shown by the solid line in FIG.

Therefore, by setting the bias voltage approximately in the middle of the saturation region as shown in FIG. 5, the output current corresponding to the oxygen concentration becomes the same regardless of the alcohol concentration as shown in FIG. 6.

Bias voltage Va and vIll in the above saturation region
FIG. 7 shows a correction curve obtained by interpolating . This characteristic decreases in proportion to the alcohol concentration from the bias voltage V9 to Vm. By correcting the bias voltage according to this characteristic, a constant m elementary concentration can be detected even if the alcohol concentration changes. As a result, the air-fuel ratio detection device is controlled to a predetermined equivalence ratio.

Examples will be described below, but the examples of the present invention are not limited to these and can be implemented in various forms without departing from the scope.

[Embodiment] FIG. 8 is a configuration diagram of an embodiment of the present invention. 1 in the configuration diagram is an engine, and this engine 1 includes a well-known lean mixture sensor 10 that detects the oxygen concentration of exhaust gas, a swirl control valve 12 that generates a strong swirl in the thin intake air, and a sensor that responds to the intake pressure. an actuator 14 that drives the swirl control valve 12;
, throttle valve 24, throttle opening sensor 26,
Surge tank 28, intake pressure sensor 30 that generates an output voltage proportional to intake negative pressure, intake manifold 32, fuel injection valve 34, spark plug 36, F-jest manifold 38, ignition coil 40, distributor 4
2, a rotation speed sensor 44, a water temperature sensor 46, and an electronic control unit (ECU) 48. The fuel injection valve 34 includes a fuel tank 50 and a fuel pump 52.
The alcohol mixed fuel is supplied via an alcohol concentration sensor 54 which detects the dielectric constant and generates an output voltage proportional to the alcohol m degree. The above lean mixture sensor 10. Each sensor of the throttle distance sensor 26, intake pressure sensor 30, rotation speed sensor 44, water temperature sensor 46, and alcohol concentration sensor 54 is ECtJ.
48.

Electronic control unit (ECtJ) 48 whose configuration is shown in Fig. 9
consists of a digital computer and a bidirectional bus 60.
A ROM (read only memory) 62, a RAM (random access memory) 64, and a C
It is equipped with a PU (microprocessor) 66, an input port 8 and an output port 0. Further, the electronic control unit 48 includes an AD converter 72 having a multiplexer function, and this AD converter 72 is connected to the input port 8.

A water temperature sensor 46 , a throttle opening sensor 26 , an alcohol concentration sensor 54 , an intake pressure sensor 30 , and a lean mixture sensor 10 are connected to the input terminals of the AD converter 72 .
6. The output signals of the alcohol concentration sensor 54, the intake pressure sensor 30, and the lean mixture sensor 10 are sequentially input to the input port 8 via the AD converter 72. Furthermore,
A rotation speed sensor 44 is connected to the input port 8 and generates an output pulse every time the engine crankshaft rotates by a predetermined crank angle. Further, the output port door 0 is connected to a bias section 7 that outputs bias voltages of the fuel injection valve 34 and the lean mixture sensor 10 via a drive circuit 74.
6 to a lean mixture sensor 10.

The alcohol concentration sensor 54 detects the alcohol concentration in the fuel injected from the fuel injection valve 34 and generates an output voltage proportional to the alcohol concentration. On the other hand, the output current value of the lean mixture sensor 10 changes in proportion to the oxygen concentration in the exhaust gas, but this output current value changes depending on the alcohol concentration in the fuel. This is shown in FIG. In FIG. 10, the vertical axis shows the output 'R current value of the lean mixture sensor 10, and the horizontal axis shows the bias voltage. Also,
In Fig. 10, actual numbers 111M1 to M4 indicate the case where only alcohol is supplied, and dashed dotted lines MG1 to MG
4 shows the case where gasoline and alcohol were mixed and supplied in almost equal amounts, and 11G1 to G4 show the case where only gasoline was fed. The above M;, MG*, and Gi (where i is 1 to 4) indicate the case of the same oxygen concentration, and the larger i is, the lower the oxygen concentration is. The bias voltage Vm in FIG. 10 is a voltage at which the detection characteristic of oxygen III when alcohol is burned becomes almost a straight line, and is at the center of the saturation characteristic portion of Mi. Similarly, Vmo is the bias voltage when alcohol and gasoline are mixed in approximately equal amounts, and (2) is the bias voltage when gasoline is used. The characteristic curve of the bias voltage and alcohol concentration is shown in FIG. Therefore, by applying the bias voltage determined from FIG. 11 according to the alcohol concentration to the lean mixture sensor 10,
The output of the lean mixture sensor 10 is no longer affected by alcohol concentration.

Next, a flowchart showing the operation of this embodiment is shown in FIG. 12 and explained. This flowchart is periodically interrupted during the processing of an air-fuel ratio control routine (not shown). First, when this bias voltage correction routine is called, the output of the alcohol concentration sensor 54 is first read (step 100). The alcohol concentration sensor 54 is
It generates an output voltage proportional to alcohol concentration. Next, alcohol concentration (alcohol/(alcohol +
The bias voltage corresponding to gasoline (gasoline))X100%) is calculated based on the graph shown in FIG. Next, the obtained bias voltage is applied to the bias section 76.
(step 120). In other words, the bias section 7
6, a bias voltage corresponding to the alcohol concentration is set. Therefore, the bias voltage of the lean mixture sensor 10 is corrected to indicate the oxygen concentration with high accuracy without being affected by the alcohol concentration.

Note that an outline of air-fuel ratio control performed using the output current of the lean mixture sensor 10 will be explained.

First, the basic injection tJ4I is determined from the engine speed and intake pressure.
Find l. Next, a target equivalence ratio (stoichiometric air-fuel ratio/target air-fuel ratio) is determined from various operating conditions. A comparison current corresponding to the target equivalence ratio is calculated and compared with the output current of the lean mixture sensor 10. Based on the result of the comparison, the basic injection amount is corrected to increase or decrease. The above is an outline of the air-fuel ratio control, and once executed, the air-fuel ratio of the engine 1 is controlled to a value corresponding to the target target equivalence ratio.

By implementing the embodiment described above, the detection output of the lean mixture sensor 10 will always be at a value corresponding to the oxygen concentration, even if the alcohol concentration in the fuel changes during driving due to fuel temperature, etc. Corrected. Therefore, the air-fuel ratio control device can always perform air-fuel ratio control with high accuracy even when the alcohol concentration of the fuel changes.

As a result, it is possible to maintain better fuel economy, pollution control, and drivability based on changes in the alcohol concentration of the fuel.

[Effects of the Invention] In the present invention described above, the detected value of the oxygen concentration detection means M4 is corrected according to the alcohol concentration so that it becomes a value corresponding to the actual equivalence ratio. Therefore, the equivalence ratio of the internal combustion engine M1 can be optimally adjusted to a predetermined value without being affected by the alcohol concentration. As a result, it is possible to provide an air-fuel ratio control device for an internal combustion engine that can maintain optimal fuel efficiency, anti-pollution measures, and drivability even if the alcohol concentration changes.

[Brief explanation of drawings]

Figure 1 is a basic configuration diagram of the present invention, Figure 2 is a diagram explaining the principle of the oxygen sensor, Figure 3 is its output characteristic graph, Figure 4 is a structural diagram of the lean mixture sensor, Figures 5 and 6. The figure is the output characteristic graph, Figure 7 is the same bias voltage characteristic graph, Figure 8 is the configuration diagram of the example, and Figure 9 is the EC of the example.
A configuration diagram of LI, FIG. 10 is a characteristic graph of the lean mixture sensor, FIG. 11 is a bias voltage characteristic graph thereof, FIG. 12 is a flowchart of the bias voltage correction routine of the embodiment, and FIG. 13 is a graph of the air-fuel ratio sensor for gasoline. Output characteristic graphs FIGS. 14 and 15 are output characteristic graphs of the oxygen concentration sensor. Ml...Internal combustion engine M2...Fuel supply means M3...Exhaust system M4...Oxygen degree detection means M5...Control means M6...Alcohol concentration correction means 1...Engine 10...・Lean mixture sensor 34...Fuel injection valve 48...Electronic control unit 54...Alcohol concentration sensor Fig. 1 Fig. 2 Fig. 3 Fig. 1 Guiasumi pressure Fig. 6 Fig. 7 'i'L near material, 100% No. 11
Figure 12 Figure 13 Temperature of alcohol Figure 14 Figure 15 Figure 15 Acid wave

Claims (1)

[Claims of Claims] Fuel supply means for supplying alcohol mixed fuel, which is a mixture of alcohol and other fuel, to an internal combustion engine, and detecting the oxygen concentration in the exhaust system of the internal combustion engine while a bias voltage is applied. oxygen concentration detection means; and controlling the fuel supply means based on the detected value of the oxygen concentration detection means to make an equivalence ratio, which is a ratio between the stoichiometric air-fuel ratio and the actual air-fuel ratio of the internal combustion engine, to a predetermined equivalence ratio. An air-fuel ratio control device for an internal combustion engine, comprising: a control means;
An air-fuel ratio control device for an internal combustion engine, comprising: alcohol concentration correction means for correcting the bias voltage of the oxygen concentration detection means based on the alcohol concentration of the alcohol mixed fuel supplied by the fuel supply means.