JPS61218746A - Air-fuel ratio controller of internal-combustion engine using alcohol-mixed fuel - Google Patents

Abstract

PURPOSE:To finely control the equivalent ratio by installing a means for correcting the standard electric-current value in accordance with the concentration of alcohol and a control means for controlling the quantity of feed of alcohol-mixed fuel. CONSTITUTION:Alcohol-mixed fuel is supplied into an engine intake passage 5, and a lean sensor 16 is installed into an engine exhaust passage 9. A concentration detecting means 30 detects the concentration of alcohol in gasoline. A correcting means 31 corrects the standard electric-current value to the value corresponding to the aimed regular equivalent ratio in accordance with the concentration of alcohol. A control means 32 compares the output electric- current value of the lean sensor 16 with the corrected standard electric-current value and controls the quantity of feed of alcohol-mixed fuel s that the equivalent ratio becomes equal to the predetermined aimed equivalent ratio. Thus, equivalent ratio can be finely controlled.

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 using alcohol mixed fuel.

[Conventional technology]

The stoichiometric air-fuel ratio when only gasoline is used is about 14.6, but the stoichiometric air-fuel ratio when only alcohol is used is about half that when only gasoline is used. Therefore, the stoichiometric air-fuel ratio when using an alcohol-mixed fuel made by mixing alcohol with gasoline is smaller than the stoichiometric air-fuel ratio when using only gasoline, and this stoichiometric air-fuel ratio changes depending on the alcohol concentration in the gasoline. Therefore, if an attempt is made to supply a mixture at a stoichiometric air-fuel ratio into an engine cylinder using alcohol mixed fuel, the amount of fuel supplied must be controlled in accordance with the alcohol concentration. For this purpose, an internal combustion engine is known that detects the alcohol concentration and controls the fuel injection amount according to the alcohol concentration so that the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes the stoichiometric air-fuel ratio (
JP-A-58-28557).

On the other hand, using alcohol mixed fuel, a 0 sensor whose output voltage changes stepwise at the stoichiometric air-fuel ratio is installed in the engine exhaust passage, and the air-fuel ratio of the mixture supplied into the engine cylinder based on the output signal of the 02 sensor. An internal combustion engine is known in which the air-fuel ratio is made to match the stoichiometric air-fuel ratio (Japanese Unexamined Patent Application Publication No. 1983
-98540 or JP-A-56-104131).

In addition, a lean sensor capable of detecting the air-fuel ratio of a lean mixture is placed in the engine exhaust passage, and the internal combustion engine is configured to match the air-fuel ratio to a predetermined lean air-fuel ratio based on the output signal of the lean sensor. The engine is also publicly known (Japanese Unexamined Patent Publication No. 58-5
(See Publication No. 7050).

[Problem that the invention seeks to solve]

When this lean sensor is used only with gasoline, the output current value of the lean sensor changes almost in proportion to the air-fuel ratio.
In this way, the air-fuel ratio can be controlled to a predetermined air-fuel ratio using the lean sensor. However, it was determined that when this lean sensor is used for alcohol-mixed fuel, the output current value of the lean sensor does not correspond in a one-to-one relationship to the equivalence ratio (=theoretical air-fuel ratio/actual air-fuel ratio). That is, even if the equivalence ratio is constant, the output current value of the lean sensor changes depending on the alcohol concentration. In other words, even if the output current value of the lean sensor is constant, the equivalence ratio at that time is not constant depending on the alcohol concentration.

Therefore, when the alcohol concentration changes, the equivalence ratio cannot be made to match the predetermined equivalence ratio based on the output current value of the lean sensor, and thus it is impossible to precisely control the equivalence ratio. There's a problem.

[Means for solving problems]

In order to solve the above problems, according to the present invention, as shown in the block diagram of the invention in FIG. , an air-fuel ratio control device that compares the output current value of the lean sensor 16 with a predetermined reference current value and controls the supply amount of alcohol mixed fuel so that the equivalence ratio becomes a predetermined target equivalence ratio. , a concentration detection means 30 for detecting the alcohol concentration in gasoline, and a correction means 31 for correcting a reference current value to a current value corresponding to a regular target equivalence ratio according to the alcohol concentration based on the detection result of the concentration detection means 30. and a control means 32 that compares the output current value of the lean sensor 16 with a corrected reference current value and controls the supply amount of alcohol mixed fuel so that the equivalence ratio becomes a predetermined target equivalence ratio. ing.

〔Example〕

Referring to Figure 2, l is the engine body, 2 is the piston, and 3
is a combustion chamber, 4 is an intake valve, 5 is an intake passage, 6 is an intake passage 5
7 is a throttle valve, 8 is an exhaust valve, 9 is an exhaust passage, and IO is a fuel injection valve arranged in the intake passage 5. The fuel injection valve 10 is connected to a fuel supply pipe 1.
1 and a fuel supply pump 12 to a fuel tank 13, and the fuel tank 13 stores gasoline containing alcohol, that is, alcohol mixed fuel.

An alcohol concentration detector 14 is disposed within the fuel supply pipe 11 to detect the alcohol concentration in the alcohol mixed fuel. A negative pressure sensor 15 that generates an output voltage proportional to the negative and positive voltages generated in the surge tank 6 is disposed within the surge tank 6, and a lean sensor 16 is disposed within the exhaust passage 9. These alcohol concentration detector 14 and negative pressure sensor 15
And the lean sensor 16 is connected to the electronic control unit 2o.

The electronic control unit 2o consists of a digital computer with ROMs interconnected by a bidirectional bus 21.
(Read-only memory) 22. RAM (Random access memory) 231. It includes a CPt1 (microprocessor) 24, an input port 25, and an output port 26. Furthermore, the electronic control unit 2o is equipped with an AD converter 27 having a multiplexer function, and this AD converter 2
7 is connected to the input port 25. An alcohol concentration detector 14 and a negative pressure sensor 15 are connected to the input terminal of the AD converter 27.
and lean sensor 16 are connected, and these alcohol concentration detector I4, negative pressure sensor 15 and lean sensor 1
The output signals of 6 are sequentially input to the input port 25 via the AD converter 27. Furthermore, a rotation speed sensor 17 is connected to the input port 25, which generates an output pulse every time the engine crankshaft rotates by a predetermined crank angle. Further, the output port 26 is connected to the fuel injection valve 1 via a drive circuit 28.
Connected to 0.

The alcohol concentration detector 14 detects the alcohol concentration in the fuel injected from the fuel injection valve 10 and generates an output voltage proportional to the alcohol concentration.

On the other hand, the output current value of the lean sensor 16 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. 3, the vertical axis IR indicates the output current value of the lean sensor 16, and the horizontal axis E indicates the equivalence ratio (=theoretical air-fuel ratio/actual air-fuel ratio).

Further, in FIG. 3, the solid line indicates the case where only gasoline is supplied, and the broken line indicates the case where only alcohol is supplied. As can be seen from Fig. 3, even when only gasoline or only alcohol is supplied, if the equivalence ratio becomes rich, the output current value [R] of the lean sensor 16 becomes small, and the air-fuel ratio becomes lean. (lean), the output current value IR increases. However, even if the equivalence ratio is the same, e.g. Eo, the linear sensor 1 changes when only gasoline is supplied (solid line) and when only alcohol is supplied (broken line).
Therefore, the output current value IR changes depending on the alcohol concentration in gasoline. The reason for this is not clear at present, but it is thought to be due to the following reasons. That is, the lean sensor 16 utilizes the fact that the amount of oxygen ions diffusing in a porous solid electrolyte such as zirconia increases in proportion to the oxygen concentration. Hydrogen in the OH group suppresses the diffusion of oxygen ions, so the higher the alcohol concentration, the lower the output current value IR.
It is assumed that the In this way, even if the equivalence ratio is the same, the lean sensor 16
Since the output current value IR of the lean sensor 16 changes to i, if the output current value IR of the lean sensor 16 is controlled to be constant, the equivalence ratio changes depending on the alcohol concentration, and thus the equivalence ratio accurately matches the predetermined equivalence ratio. It is difficult to force them to do so. Therefore, the present invention attempts to control the equivalence ratio so that it accurately matches a predetermined equivalence ratio even if the alcohol concentration changes. Next, the air-fuel ratio control method according to the present invention will be explained with reference to the flowchart shown in FIG.

Referring to FIG. 5, first, in step 102, the output signal of the rotation speed sensor 17 representing the engine rotation speed N is taken in to calculate the engine rotation speed N, and then in step 104, the negative pressure representing the intake pipe negative pressure P is calculated. Take in the output signal of the sensor 15. Then in step 106 the ROM 22
The basic injection amount TAUO is determined from the relationship between N, P, which is stored in advance in the form of a map, and the basic injection ff1TAIIo. Next, in step 108, it is determined whether or not the operating state is one in which feed bank control is performed, and if the operating state is not one in which feedback control is performed, the routine moves to a routine for executing a fuel injection action. If the operating state is one in which feedback control is to be performed, the process proceeds to step 110, where a comparison current value IRo, that is, a reference for feedback control, is determined from the relationship between N, P, which is stored in advance in the form of a map in the ROM 22, and the comparison current value IRO. Find the reference current value IRo. This comparison current value or reference current value IRo is determined based on the case where only gasoline is used as shown in FIG. 3, and corresponds to the equivalence ratio E0 when only gasoline is used. That is, N.

Optimal target equivalence ratio E0 according to the operating condition determined by P
exists and the target equivalence ratio E when only gasoline is used.

Comparison current value or reference current value IRo and N, P when
The relationship between the two is stored in advance in the ROM 22 in the form of a map. When the comparison current value or reference current value rRa is determined from N and P in step 110, the process proceeds to step 112, where the alcohol concentration detector 1 representing the alcohol concentration is detected.
Take in the output signal of 4. Next, in step 114, a correction coefficient K determined by the alcohol concentration F is determined from the relationship shown in FIG. 4, which is stored in the ROM 22 in advance. As can be seen from FIG. 4, this correction coefficient is 1.0 when the alcohol concentration F is 0%, and gradually becomes smaller than 1.0 as the alcohol concentration F increases. Next, in step 116, IR, is multiplied by K, and the result is set as the comparison current value or reference current value rR0. Therefore I
Ro changes depending on the alcohol concentration F, and when the alcohol concentration F is 0%, it becomes IR, which corresponds to point X in Figure 3, and when the alcohol concentration F is 100%, it becomes IR, which corresponds to point X in Figure 3.
IR corresponding to the point. The value of K in FIG. 4 is determined so that when the alcohol concentration F is between 0% and 100%, IR corresponds to the target equivalence ratio E0.

That is, the reference current value IR, is corrected to a current value corresponding to the normal target equivalence ratio E0 according to the alcohol concentration F, and thus IR, corresponds to the target equivalence ratio E0 regardless of the alcohol concentration F. become. Next, in step 118, the output signal IR of the lean sensor 16 is taken in, and in step 120, TR and IRo are compared, IR>
If it is I RQ, that is, if it is lean compared to the target equivalence ratio E0, then in step 122 TAUo is set to a constant value α.
is added to increase the fuel injection amount, and as a result, the equivalence ratio E
approaches the target equivalence ratio E0, and unless IR>IRo,
That is, if it is rich compared to the target equivalence ratio E6, step 1
24, a constant value α is subtracted from TAIJo to reduce the fuel injection amount, and as a result, the equivalence ratio E becomes the target equivalence ratio E0.
approach. In this way, the target equivalence ratio E0 can be precisely controlled regardless of the alcohol concentration F.

〔Effect of the invention〕

When alcohol mixed fuel is used, the equivalence ratio can be made to accurately match the predetermined target equivalence ratio regardless of the alcohol concentration.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of the present invention, Figure 2 is an overall diagram of the internal combustion engine,
Figure 3 is a diagram showing the relationship between comparison current value or reference current value and equivalence ratio, Figure 4 is a diagram showing the relationship between correction coefficient and alcohol concentration F, and Figure 5 is a diagram showing air-fuel ratio control. A flowchart is shown below. 5...Intake passage, 9...Exhaust passage, 10...
Fuel injection valve, 14... Alcohol concentration detector, 16... Lean sensor, 20... Electronic control unit.

Claims (1)

[Claims] Alcohol mixed fuel is supplied into the engine intake passage, a lean sensor is provided in the engine exhaust passage, and the output current value of the lean sensor is compared with a predetermined reference current value to determine the target equivalence ratio. The air-fuel ratio control device is configured to control the supply amount of alcohol mixed fuel so that the ratio of alcohol to alcohol is maintained. a correction means for correcting the current value to correspond to a regular target equivalence ratio according to the concentration; and a correction means that compares the output current value of the lean sensor with the corrected reference current value so that the equivalence ratio becomes a predetermined target equivalence ratio. An air-fuel ratio control device for an internal combustion engine for alcohol-mixed fuel, comprising a control means for controlling the supply amount of alcohol-mixed fuel.