JPH041181B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an air-fuel ratio control device 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 surface of a zirconia plate, a thin film that serves as an anode is coated on the other surface 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. Note that since this oxygen concentration detector detects the oxygen concentration in the exhaust passage, it is possible to detect the air-fuel ratio when the air-fuel mixture supplied into the engine cylinder is a lean air-fuel mixture. On the other hand, when no voltage is applied between the anode and cathode of the zirconia plate in this oxygen concentration detector, the oxygen concentration in the gas that contacts one surface of the zirconia plate and the gas that contacts the other surface of the zirconia plate An electromotive force is generated due to the concentration difference with the oxygen concentration in the engine cylinder, and by utilizing this property, it is determined whether the air-fuel mixture supplied into the engine cylinder is higher than the stoichiometric air-fuel ratio. In an internal combustion engine, it is necessary to adjust the air-fuel ratio of the air-fuel mixture supplied into the engine cylinders to the stoichiometric air-fuel ratio or to a lean mixture depending on the engine operating conditions. When used, the air-fuel ratio can be precisely controlled over a wide range.

An object of the present invention is to provide an air-fuel ratio control device that can accurately feedback control the air-fuel ratio to either the stoichiometric air-fuel ratio or a predetermined lean side air-fuel ratio using a single oxygen concentration detector. .

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.
Fuel is injected from these fuel injection valves 15 toward the corresponding intake ports 7. 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 this 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, an oxygen concentration detector 20 is attached to the exhaust manifold 13, and this oxygen concentration detector 20 is connected to the electronic control unit 14. As shown in FIG. 2, the oxygen concentration detector 20 includes, for example, a cup-shaped oxygen ion conductive solid electrolyte 21 made of zirconia, and a porous ceramic 22 covering the outer peripheral surface of the electrolyte. Placed in a gas stream. Further, a thin platinum film for an anode and a thin platinum film for a cathode are coated on the inner and outer peripheral surfaces of the oxygen ion conductive fixed electrolyte 21, respectively, and these platinum thin films are connected to a switching circuit 24 via lead wires 23a and 23b. be done. As shown in FIG. 2, the switching circuit 24 includes three switching switches 25a, 2
5b, 25c, a power supply 26, and a resistor 27, and as described later, each changeover switch 25a, 25
b and 25c are switched and controlled at the same time. The changeover switch 25a consists of a movable contact d connected to a lead wire 23a and a pair of fixed contacts e and f, while the changeover switch 25b consists of a movable contact g connected to an output terminal 28a and a pair of fixed contacts h and f. Consisting of Further, the changeover switch 25c includes a movable contact k connected to the output terminal 28b and a pair of fixed contacts l and m. A fixed contact e of the changeover switch 25a is connected to a fixed contact l of the changeover switch 25c, and a fixed contact m of the changeover switch 25c is connected to the lead wire 23b. In addition, the fixed contact e of the changeover switch 25a
A power supply 2 is connected between the fixed contact m of the changeover switch 25c and
6 and a resistor 27 are connected in series, and these power supplies 2
6 and the resistor 27 can be connected to a fixed contact h of the changeover switch 25b.

Each changeover switch 25a, 25b, 25c is
When the connection is as shown in the figure, lead wire 2
A voltage from a power supply 26 is applied between 3a and 23b.
At this time, the 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, where the oxygen molecules endowed with electrons become oxygen ion conductive. After passing through the solid electrolyte 21, the electrons 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 power 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. In addition,
As shown in FIG. 2, the output terminals 28a and 28b are connected to both ends of the resistor 27.
A voltage proportional to the generated current is generated between a and 28b, and therefore the vertical axis in FIG. 5 can be considered to represent the output voltage V. A state in which the output voltage V is proportional to the oxygen concentration is referred to as a first detection state.

On the other hand, as shown by the broken line in FIG. 2, the movable contact d of the changeover switch 25a is connected to the fixed contact f, the movable contact g of the changeover switch 25b is connected to the fixed contact f, and the movable contact k of the changeover switch 25c is fixed. The state where the contact point m is connected is called a second detection state. At this time, the lead wires 23a and 23b are directly connected to the output terminals 28a and 28b, and the lead wire 23
No voltage is applied between a and 23b. At this time, the oxygen concentration detector 20 functions as a concentration battery, and detects the oxygen concentration in the exhaust manifold 13 and the oxygen concentration in the atmosphere, that is, the oxygen ion conductive solid electrolyte 2.
A voltage as shown in FIG. 6 is generated between both sides of the oxygen ion conductive solid electrolyte 21 due to the difference in oxygen concentration between the gases in contact with both sides of the solid electrolyte 21 . In FIG. 6, the vertical axis V shows the voltage, and the horizontal axis A/F shows the air-fuel ratio. Therefore, in the second detection state, when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, the output terminals 28a and 28b
When an output voltage of about 0.9 volts is generated between the output terminals 28 and the air-fuel ratio is larger than the stoichiometric air-fuel ratio,
It can be seen that an output voltage of about 0.1 volt is generated between a and 28b. In this way, in the second detection state, it is possible to detect whether the air-fuel ratio is larger or smaller than the stoichiometric air-fuel ratio.

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 the buffer 37 and the AD converter 3.
8 to the input port 33. The negative pressure sensor 18 detects the negative pressure generated within the surge tank 12,
That is, it generates an output voltage proportional to the intake pipe negative pressure P,
This output voltage is converted into a corresponding binary number at the AD converter 38, and this binary number is converted to the input port 33.
It is also input to the MPU 30 via 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. Further, the output terminal of the oxygen concentration detector 20 is connected to the switching circuit 24 as described above, and this switching circuit 24
is connected to the input port 33 via an amplifier 40 and an AD converter 41. The output voltage of the switching circuit 24 is converted into a corresponding binary number by the AD converter 41, and this binary number is input to the MPU 30 via the input port 33 and the bus 35. Note that the relationship between the output voltage V and the air-fuel ratio A/F, indicated by the solid line K in FIG. 5, is stored in advance in the ROM 32 in the form of a function or a data table.

The output port 34 is provided so that the switching circuit 24 outputs data for operating each of the switching switches 25a, 25b, and 25c as well as data for operating the fuel injection valve 15. Binary data is written from the MPU 30 via the bus 35. The output terminal of the output port 34 is connected to the switching circuit 24 on the one hand and to the input terminal of the down counter 43 on the other hand. Therefore, each changeover switch 25a, 25b, 25
c is controlled to switch to either the first detection state or the second detection state based on the data written to the output port 34. On the other hand, the down counter 43
is provided to convert the binary data written from the MPU 30 into the corresponding time length, and this down counter 43 counts down the data sent from the output port 34 to the clock generator 36. It starts with a clock signal, completes counting when the count value reaches 0, and generates a count completion signal at the output terminal. S-
The reset input terminal R of the R flip-flop 44 is connected to the output terminal of the down counter 43, and the S-
The set input terminal S of R flip-flop 44 is connected to clock generator 36. This S-R flip-flop 44 is set by the clock signal of the clock generator 36 at the same time as the down count starts, and when the down count is completed, the down counter 4 is set.
It is reset by the count completion signal of 3.
Therefore, the output terminal Q of the S-R flip-flop 44
is at a high level while the down count is being performed. Output terminal Q of S-R flip-flop 44
is connected to the fuel injection valve 15 via the power amplification circuit 45, and therefore, it can be seen that the fuel injection valve 15 is energized 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 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 step 50
Then, the target air-fuel ratio is calculated from the relationship shown in FIG. As can be seen from Fig. 7, this target value is the stoichiometric air-fuel ratio when the engine speed N is lower than approximately 1000 r.pm and when it is higher than approximately 4000 r.pm, and when the engine speed N is approximately 1000 r.pm. from pm
Between 4000rpm, the air-fuel ratio is on the lean side as shown in the numbers. After the target air-fuel ratio is determined in step 50, the basic fuel injection time τ ₀ is then calculated in step 51. This basic fuel injection time is the time required to form a mixture with an air-fuel ratio as shown in Fig. 7, and this basic fuel injection time τ ₀ is the same as shown in Fig. ROM3 in the form of a map as a function of P and engine speed N.
It is stored in 2. Next, in step 52, it is determined whether or not the target air-fuel ratio is on the lean side. If the target air-fuel ratio is on the lean side, the process proceeds to step 53. In step 53, the changeover switches 25a, 25b, and 26c of the changeover circuit 24 are changed over as shown in FIG. 2 to bring them into the first detection state. Then step 54
Then, the target output voltage value V ₀ of the switching circuit 24 is calculated from the relationship shown in FIG. Then step 55
Then, it is determined whether the current output voltage value V of the switching circuit 20 is not smaller than the target voltage value _V0 . If it is determined in step 55 that the current output voltage value V is not smaller than the target voltage value _V0 , then in step 56 a constant value α is added to the correction coefficient f, and after setting the addition result to f, the process proceeds to step 57. . On the other hand, when it is determined in step 55 that the current output voltage value V is smaller than the target voltage value _V0 , a constant value β is subtracted from the correction coefficient f in step 58, and after setting the subtraction result to f, the process proceeds to step 57. Proceed to. In step 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 the fuel injection time τ. FIG. 8 shows changes in the output voltage V of the switching circuit 24 and the correction coefficient f. As shown in FIG. 8, when the output voltage V of the switching circuit 24 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, the fuel injection amount is increased, and on the other hand, when the output voltage V of the switching circuit 24 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 β
Since the fuel injection amount is gradually decreased, the fuel injection amount is decreased.

On the other hand, if it is determined in step 52 that the target air-fuel ratio is not on the lean side, that is, the target air-fuel ratio is
When the air-fuel ratio is the stoichiometric air-fuel ratio, as shown by the hatching in the figure, the process proceeds to step 59. In step 59, each changeover switch 25a, 25b,
25c is activated to switch to the second detection state shown by the broken line. Next, in step 60, it is determined whether the output voltage V of the switching circuit 24 is not smaller than the reference voltage Vr shown in FIG. Note that this reference voltage Vr is stored in the ROM 32 in advance. When it is determined in step 60 that the output voltage V of the switching circuit 24 is smaller than the reference voltage Vr, that is, when the air-fuel ratio is larger than the stoichiometric air-fuel ratio, the process proceeds to step 61.
γ is added to the correction coefficient f, and the addition result is set as f. Therefore, at this time, the fuel injection time τ is gradually increased. On the other hand, step 60
, the output voltage V of the switching circuit 24 is the reference voltage
When it is determined that the air-fuel ratio is not smaller than Vr, that is, when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, step 62
δ is subtracted from the correction coefficient f, and the subtraction result is set as f. Therefore, at this time, the fuel injection time τ is gradually increased. In this way, the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio.

As described above, according to the present invention, by using a single oxygen concentration detector, the air-fuel mixture supplied into the engine cylinder is The fuel ratio can be accurately feedback-controlled to the target air-fuel ratio.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an internal combustion engine according to the present invention;
Fig. 2 is a circuit diagram of the switching circuit of the oxygen concentration detector, 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 circuit diagram of the switching circuit of the oxygen concentration detector. FIG. 6 is a diagram showing the output voltage of the oxygen concentration detector in the detection state, FIG. 6 is a diagram showing the output voltage of the oxygen concentration detector in the second detection state, and FIG.
8 is a diagram showing the target air-fuel ratio, and FIG. 8 is a diagram showing changes in the correction coefficient. 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... Oxygen Concentration detector.

Claims (1)

[Claims] 1. An oxygen concentration detector capable of detecting the oxygen concentration in exhaust gas is installed in the engine exhaust passage, and the air-fuel ratio of the air-fuel mixture supplied into the engine cylinders is feedback-controlled based on the output signal of the oxygen concentration detector. In the air-fuel ratio control device, a cathode and an anode are respectively formed on the outer peripheral surface and the inner peripheral surface of the oxygen ion conductive solid electrolyte, and a diffusion passing means through which oxygen molecules pass by diffusion is provided on the oxygen ion conductive solid electrolyte. An oxygen concentration detector provided around the outer circumferential surface of the oxygen ion conductive solid electrolyte so that oxygen molecules in the exhaust gas reach the outer circumferential surface of the oxygen ion conductive solid electrolyte through the diffusion passage means, the oxygen concentration detector being provided between the cathode and the anode. When a voltage is applied, it generates an output current proportional to the oxygen concentration in the exhaust gas, and when the voltage application is stopped, it acts as a concentration cell to indicate whether the air-fuel ratio is greater than the stoichiometric air-fuel ratio. An oxygen concentration detector that generates an output voltage is used, and a switching circuit is provided to apply the voltage or stop applying the voltage, and the air-fuel ratio should be set to the stoichiometric air-fuel ratio depending on the operating state of the engine, or the air-fuel ratio should be set in advance. The oxygen concentration detector is equipped with a storage means that stores information as to whether the air-fuel ratio should be set to a predetermined lean air-fuel ratio, and when the switching circuit is switched and controlled based on the stored information to bring the air-fuel ratio to the stoichiometric air-fuel ratio, the oxygen concentration detector An internal combustion engine in which the air-fuel ratio is feedback-controlled based on the output voltage, and when the air-fuel ratio should be set to a predetermined lean side air-fuel ratio, the air-fuel ratio is feedback-controlled based on the output current of the oxygen concentration detector. Air-fuel ratio control device.