JPH0325625B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an air-fuel ratio control method for an internal combustion engine.

As an oxygen concentration detector capable of detecting the oxygen concentration in a gas, there is an oxygen concentration detector using an oxygen ion conductive solid electrolyte such as zirconia, as described in Japanese Patent Application Laid-Open No. 52-72286. It is publicly known. In this oxygen concentration sensor, a thin film that serves as a cathode is coated on one side of the zirconia plate, a thin film that serves as an anode is coated on the other side of the zirconia plate, and a voltage is applied between the cathode and the anode. Oxygen molecules, which have been given electrons upon contact with the cathode, pass through the zirconia plate and then emit electrons at the anode, generating a current from the anode to the cathode, and this current causes the oxygen passing through the zirconia plate Since it is proportional to the number of molecules, that is, the partial pressure of oxygen in the gas that contacts the cathode, the oxygen concentration can be determined from this current value. Therefore, if this oxygen concentration detector is installed in the engine exhaust passage, the oxygen concentration in the exhaust passage can be detected, and therefore the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder can be known. Since this oxygen concentration detector detects the oxygen concentration in the exhaust passage, it functions as a detector when the air-fuel mixture supplied to the engine cylinder is a lean mixture. Such an oxygen concentration detector will be referred to as a lean sensor hereinafter.

One method of controlling the air-fuel ratio using such a lean sensor is to directly control the fuel injection time based on the output signal of the lean sensor so that the air-fuel ratio becomes a predetermined air-fuel ratio. In many cases, the basic fuel injection time required to form a mixture with a predetermined air-fuel ratio is calculated from the engine speed and intake pipe negative pressure or from the output signal of an air flow meter, and this basic fuel injection The time is corrected based on the output signal of the lean sensor. The air-fuel ratio required by the engine varies depending on the operating state of the engine, and therefore, especially when calculating the basic fuel injection time from the engine speed and intake pipe negative pressure, it is necessary to calculate the air-fuel ratio experimentally as a function of the engine speed and intake pipe negative pressure. The basic fuel injection time determined by is stored in advance, and fuel is injected based on the stored basic fuel injection time. However, when fuel is injected based on the basic fuel injection time stored in this way, changes in the fuel injection valve over time,
For example, the fuel injection amount may be reduced from the initial injection amount due to a blockage in the fuel injection port, and as a result, even if fuel is injected based on the basic fuel injection time, the air-fuel mixture formed by this injected fuel will be reduced. The air-fuel ratio deviates from the predetermined air-fuel ratio. Even if the air-fuel ratio deviates from the predetermined air-fuel ratio in this way, the feedback control by the lean sensor will gradually make it match the predetermined air-fuel ratio. Because of this, there is a problem that not only good operation cannot be obtained, but also exhaust emissions are deteriorated.

The present invention corrects the basic fuel injection time so as to offset changes in the fuel injection amount over time, thereby making the air-fuel ratio of the air-fuel mixture formed by the injected fuel match a predetermined air-fuel ratio. An object of the present invention is to provide an air-fuel ratio control method that achieves the following.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, 1 is the engine body, 2 is the cylinder block, 3 is the piston that reciprocates within the cylinder block 2, and 4 is the cylinder block 2.
Cylinder head fixed on top, 5 is piston 3
and a combustion chamber formed between the cylinder head 4, 6 an ignition plug disposed within the combustion chamber 5, 7 an intake port, 8 an intake valve, 9 an exhaust port, and 10 an exhaust valve. The intake port 7 is connected to a common surge tank 12 via a branch pipe 11, while the exhaust port 9 is connected to an exhaust manifold 13. Each branch pipe 11 is provided with a fuel injection valve 15 that is controlled by an output signal from an electronic control unit 14, and from these fuel injection valves 15, a corresponding intake port 7 is provided.
Fuel is injected towards. The surge tank 12 is connected to an air cleaner (not shown) via an intake pipe 16, and a throttle valve 17 connected to an accelerator pedal is disposed within the intake pipe 16. A negative pressure sensor 18 is installed inside the surge tank 12,
The negative pressure sensor 18 and the rotational speed sensor 19 are connected to the electronic control unit 14. On the other hand, a lean sensor 20 is attached to the exhaust manifold 13, and this lean sensor 20 is connected to the electronic control unit 1.
Connected to 4. The lean sensor 20 is, for example, a second
As shown in the figure, it comprises a cup-shaped oxygen ion conductive solid electrolyte 21 made of zirconia and a porous ceramic 22 covering its outer peripheral surface, and this porous ceramic 22 is placed in the exhaust gas flow.
Further, a platinum thin film for an anode and a platinum thin film for a cathode are coated on the inner and outer peripheral surfaces of the oxygen ion conductive solid electrolyte 21, respectively, and a voltage is applied between the lead wires 23 and 24 connected to these platinum thin films. applied. Oxygen molecules in the exhaust gas pass through the porous ceramic 22 by diffusion and reach the cathode platinum thin film of the oxygen ion conductive solid electrolyte 21,
After the oxygen molecules imparted with electrons pass through the oxygen ion conductive solid electrolyte 21, they come into contact with the anode platinum thin film of the oxygen ion conductive solid electrolyte 21 and emit electrons, thereby generating an electric current. FIG. 5 shows the relationship between the oxygen concentration P (weight percent) in the exhaust gas and the generated current A (mA).
As shown by the solid line K in FIG. 5, it can be seen that the generated current A is approximately proportional to the oxygen concentration. Note that if the oxygen concentration in the exhaust gas is known, the air-fuel ratio supplied into the engine cylinder can be found, and this air-fuel ratio is shown on the horizontal axis A/F in FIG. Therefore, it can be seen from FIG. 5 that if the generated current is known, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder can be detected.

FIG. 3 shows the electronic control unit 14. Referring to FIG. 3, the electronic control unit 14 is composed of a digital computer, in which a microprocessor (MPU) 30 that performs various calculation processes, a random access memory (RAM) 31, control programs, calculation constants, etc. are stored in advance. A read-only memory (ROM) 32, an input port 33, and an output port 34 are interconnected via a bidirectional bus 35. Furthermore, a clock generator 36 is provided within the electronic control unit 14 for generating various clock signals. As shown in FIG. 3, the negative pressure sensor 18 is connected to a buffer 37 and an AD converter 38.
It is connected to the input port 33 via. The negative pressure sensor 18 generates an output voltage proportional to the negative pressure generated in the surge tank 12, that is, the intake pipe negative pressure P, and this output voltage is outputted to the corresponding 2
The binary number is converted into a base number and inputted to the MPU 30 via the input port 33 and the bus 35.
On the other hand, the rotation speed sensor 19 is connected to the input port 33 via a buffer 39. This rotation speed sensor 19 generates a pulse every time the engine crankshaft rotates by a predetermined crank angle, and this pulse is transmitted to the MPU 30 via an input port 33 and a bus 35.
is input. In MPU30, rotation speed sensor 19
The engine speed is calculated from the output pulse. Furthermore, the lean sensor 20 is connected to the input port 33 via a current-voltage converter 40, an amplifier 41, and an AD converter 42. The current generated by the lean sensor 20 is converted into a corresponding voltage in a current-voltage converter 40, and this voltage is then converted into a corresponding binary number in an AD converter 42, and this binary number is transmitted via an input port 33 and a bus 35. MPU30
is input. The relationship shown by the solid line K in FIG. 5 is stored in advance in the ROM 32, but in this case, the vertical axis in FIG.
In the ROM 32, the relationship between the voltage V and the oxygen concentration P shown by the solid line K in FIG. 5 is stored in the form of a data table or function.

The output port 34 is provided to output data for operating the fuel injection valve 15, and the binary data is sent to the MPU 3.
0 via bus 35. Each output terminal of the output port 34 is connected to a corresponding input terminal of the down counter 43. This down counter 43 is provided to convert the binary data written from the MPU 30 into the corresponding time length.
starts counting down the data sent from the output port 34 in response to the clock signal from the clock generator 36, and when the count value reaches 0, the count is completed and a count completion signal is generated at the output terminal. The reset input terminal R of the S-R flip-flop 44 is connected to the output terminal of the down counter 43, and the set input terminal S of the S-R flip-flop 44 is connected to the clock generator 36. This S-R flip-flop 44 is connected to the clock generator 3.
It is set simultaneously with the start of down counting by the clock signal No. 6, and reset by the count completion signal of the down counter 43 when the down counting is completed. Therefore, the output terminal Q of the S-R flip-flop 44 is at a high level while the down count is being performed. The output terminal Q of the S-R flip-flop 44 is connected to the fuel injection valve 15 via a power amplification circuit 45.
It can be seen that is activated while the down counter 43 is counting down.

Next, the operation of the air-fuel ratio control device according to the present invention will be explained with reference to FIG. Referring to FIG. 4, first, in step 50, the negative pressure sensor 18 is
The target air-fuel ratio is set from the output signal of the rotation speed sensor 19. This target air-fuel ratio is stored in advance in the ROM 32 as a function of the engine load, for example, the intake pipe negative pressure P and the engine speed N, as shown in FIG. 7, for example. Note that the numerical values in FIG. 7 indicate the air-fuel ratio.
Therefore, in step 50, the target air-fuel ratio is calculated from the relationship shown in FIG. Next, when the target air-fuel ratio is determined, in step 51, the lean sensor 2 is
A target output voltage value V ₀ of 0 is calculated, and then in step 52 a basic fuel injection time τ ₀ is calculated. This basic fuel injection time τ ₀ is the time required to form a mixture with an air-fuel ratio as _shown in FIG. For example, it is stored in advance in the ROM 32 in the form of a map as a function of the intake pipe negative pressure P and the engine speed N. Next, in step 53, it is determined whether the intake pipe negative pressure P and the engine speed N are within a predetermined range, and if the intake pipe negative pressure P and the engine speed N are not within the predetermined range. The process proceeds to step 54, where Σf is set to 0, and then the process proceeds to step 55. In step 55, lean sensor 20
It is determined whether the current output voltage value V of is not smaller than the target voltage value _V0 . When it is determined in step 55 that the current output voltage value V is not smaller than the target voltage value _V0 , a constant value α is added to the correction coefficient f in step 56, and after setting the addition result to f, the process proceeds to step 57. move on. On the other hand, step
At 55, the current output voltage value V is the target voltage value V ₀
If it is determined that the constant value β is smaller than the correction coefficient f, the constant value β is subtracted from the correction coefficient f in step 58, and the subtraction result is set as f, and then the process proceeds to step 57. step
At 57, the basic fuel injection time τ ₀ is multiplied by the correction coefficient f to calculate the fuel injection time τ, and fuel is injected from the fuel injection valve 15 for a time corresponding to this fuel injection time τ. FIG. 6 shows changes in the output voltage V of the lean sensor 20 and the correction coefficient f. As shown in FIG. 6, when the output voltage V of the lean sensor 20 becomes larger than the target voltage value _V0 , that is, when the air-fuel ratio becomes larger than the target air-fuel ratio, the correction coefficient f is increased by α, so that the fuel injection amount is increased. On the other hand, when the output voltage V of the lean sensor 20 becomes smaller than the target voltage value _V0 , that is, when the air-fuel ratio becomes smaller than the target air-fuel ratio, the correction coefficient f is reduced by β, so that the fuel injection amount is be reduced.

On the other hand, in step 53, as mentioned above, the engine speed N is set within a predetermined range, for example 1980r.pm (=
N ₁ ) < N < 2020r.pm (=N ₂ ), and the intake pipe negative pressure P is within a predetermined range, e.g. -360mmHg
It is determined whether or not (=P ₁ )<P<-340mmHg (=P ₂ ), and if it is within the above range, step 59 is performed.
Proceed to. In step 59, it is determined whether 5 seconds have elapsed or not. When 5 seconds have elapsed, the process proceeds to step 60, where a correction coefficient f is added. Then step 61
Then, it is determined whether 5 seconds have passed or not.
When seconds have elapsed, the process advances to step 62. Therefore, at this time, Σf indicates the sum of the correction coefficients f for 5 seconds.
In step 62, Σf is divided by the number of additions n in step 60, and the result of the division is set as . Therefore, this shows the average value of the correction coefficient f over 5 seconds. Next, in step 63, is divided by _f0 , and the result of the division is designated as K. As shown in FIG. 6, this f ₀ is a predetermined reference value for the correction coefficient f, and this reference value f ₀ is, for example, 1.0. As mentioned above, for example, if the engine speed N is 1980r.
When the range is pm<N<2020r.pm and the intake pipe negative pressure P is in the range -360mmHg<P<-340mmHg, the target air-fuel ratio is 22
Therefore, the basic fuel injection time τ ₀ is the target air-fuel ratio
This is the injection time required to form a mixture of 22. However, due to changes over time, for example, if the nozzle port of the injection valve becomes clogged, the fuel injection amount will decrease even if the fuel is injected for the basic fuel injection time τ _0. For example, the amount of fuel injected based on the basic fuel injection time τ ₀ will decrease. The resulting air-fuel ratio will be around 25. At this time, the air-fuel ratio is controlled by the lean sensor 20 so that it becomes the target air-fuel ratio 22, so the value of the correction coefficient f inevitably becomes large. Therefore, K=/f ₀ mentioned above indicates the deviation of the basic fuel injection time τ ₀ from the predetermined air-fuel ratio. Therefore, in step 64, the basic fuel injection time τ ₀ stored in the map is multiplied by K, and the multiplication result is set as the basic fuel injection time τ ₀ . That is, this means that the basic fuel injection time τ ₀ stored in the map has been rewritten. Next, in step 65, Σf is set to 0, and then the process proceeds to step 55.

As described above, according to the present invention, the target air-fuel ratio changes depending on the engine speed and the engine load, the basic fuel injection amount necessary to set the air-fuel ratio to the target air-fuel ratio, and the basic fuel injection amount that corresponds to the target air-fuel ratio. The target output value of the lean sensor is stored in advance, and the basic fuel injection amount is corrected to increase or decrease using a correction coefficient that increases or decreases around the reference value so that the lean sensor output value becomes the target output value. The air-fuel ratio can be accurately controlled to the target air-fuel ratio. Also,
The average value of the correction coefficients is calculated, and when the average value of the correction coefficients deviates from the reference value, the stored value of the basic fuel injection amount is updated so that the average value of the correction coefficients becomes the reference value. For example, even if a fuel injection port is clogged, if fuel is injected based on the basic fuel injection amount, the air-fuel ratio will be the target air-fuel ratio. As a result, even if, for example, the fuel injection port becomes clogged due to changes over time, the air-fuel ratio will follow the change in the target air-fuel ratio and change with good responsiveness when the operating conditions of the engine change and the target air-fuel ratio changes. , thus ensuring good engine operation.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of an internal combustion engine according to the present invention;
Fig. 2 is a side sectional view of the lean sensor, Fig. 3 is a circuit diagram of the electronic control unit, Fig. 4 is a flowchart for explaining the operation of the air-fuel ratio control device, and Fig. 5 is a flowchart for explaining the operation of the air-fuel ratio control device.
FIG. 6 is a diagram showing the relationship between the output of the lean sensor and oxygen concentration, FIG. 6 is a diagram showing changes in the correction coefficient, and FIG. 7 is a diagram showing the target air-fuel ratio. 12... Surge tank, 13... Exhaust manifold, 14... Electronic control unit, 15... Fuel injection valve, 17... Throttle valve, 18... Negative pressure sensor, 19... Rotation speed sensor, 20... Lean sensor.

Claims (1)

[Claims] 1. A lean sensor whose output value changes according to the air-fuel ratio is placed in the engine exhaust passage, and the target air-fuel ratio, which changes according to the engine speed and engine load, is stored in advance as a function of the engine speed and engine load. Furthermore, the basic fuel injection amount required to set the air-fuel ratio to the target air-fuel ratio is stored in advance as a function of engine speed and engine load, and the lean sensor output value corresponding to the target air-fuel ratio is set as the target output value. The air-fuel ratio is adjusted to the target air-fuel ratio by increasing or decreasing the basic fuel injection amount using a correction coefficient that is stored in advance and increases or decreases around the reference value so that the lean sensor output value becomes the target output value. is controlled to calculate the average value of the correction coefficient, and when the average value of the correction coefficient deviates from the reference value, updates the stored value of the basic fuel injection amount so that the average value of the correction coefficient becomes the reference value. An air-fuel ratio control method for an internal combustion engine.