JPS5857050A - Air-fuel ratio control device of internal-combustion engine - Google Patents

Abstract

PURPOSE:To control the air-fuel ratio precisely at a target value invariably by determining the aging variation and calculating the correction coefficient based on the output of a lean sensor under a condition that an exhaust passage is filled with the atmosphere before starting an engine or after the operation is stopped. CONSTITUTION:A lean sensor 22 generating an output signal in proportion to the oxygen density is fitted to an exhaust manifold 13, and a fuel injection valve 15 is controlled to control the air-fuel ratio by means of an electronic control unit 14 so that the output of the lean sensor 22 coincides with the value based on the predetermined oxygen density. A judging unit judging whether the exhaust manifold 13 is filled with the atmosphere or not is provided in said control unit 14. When the exhaust manifold 13 is filled with the atmosphere after the engine operation is stopped or the like, the present output of the sensor 22 is compared with the previously stored memory content, then the aging variation and the correction coefficient are determined based on the deviation.

Description

[Detailed description of the invention] The present invention provides an air-fuel ratio control device Kl for an internal combustion engine.

As an oxygen concentration detector capable of detecting oxygen am in a gas, for example, as described in JP-A-52-72286, an oxygen concentration detector using an oxygen ion conductive solid 11N substance such as norconia is used. Detectors are known. In this oxygen concentration sensor, a thin film forming a cathode is coated on the 10III surface of the zirconia plate, and a thin film forming a VC anode is coated on the 0111 surface of the zirconia plate, thereby applying a voltage between the cathode and the anode. Oxygen molecules that have been given electrons by contacting 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 flows through the zirconia plate. Since it is proportional to the number of oxygen molecules passing through, 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, by installing this oxygen concentration detector in the engine exhaust passage, it is possible to detect the oxygen concentration in the exhaust passage and thereby know the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder. 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. However, when this lean sensor is installed in the engine exhaust passage, the resistance value at the interface between the electrode thin film and the zirconia plate increases due to deterioration of the electrode due to high-temperature exhaust gas, or the resistance value at the interface between the electrode thin film and the zirconia plate increases, or the P, Zm contained in the exhaust gas increases. , F., Pb, etc., and physical destruction due to thermal shock, which causes porous ceramics to cover the outer peripheral surface of the zirconia plate. The current value gradually increases or decreases over time even at the same oxygen concentration due to changes in the diffusion rate and amount of oxygen gas within the layer. If the air-fuel ratio is controlled to the target air-fuel ratio based on this current value, the target air-fuel ratio will change over time, and the air-fuel ratio will be accurately adjusted to the initially set target air-fuel ratio. This results in the problem of loss of control.

The present invention provides air-fuel ratio control that automatically calibrates the current value even if the output current value of the lean sensor changes due to changes over time, thereby accurately controlling the air-fuel ratio to the initially set target air-fuel ratio. The goal is to provide equipment.

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 Glock 2, 4 is the cylinder head fixed on the cylinder GLOCK 2, and 5 is the piston 3 and the cylinder head. A combustion chamber formed between 4 and a 6Fi combustion chamber 5, an ignition plug disposed within the 6Fi combustion chamber 5,
7 is an intake port, 8 is an intake valve, 9ii is an exhaust port, 10
shows the 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 the 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 fuel is injected from these fuel injection valves 15 toward the corresponding intake port 7. The surge tank 12 has [trachea 16. It is connected to the atmosphere via an air flow meter 17 and an air cleaner (not shown). A throttle valve 18 is arranged in the trachea 16, and this throttle valve 18 is connected to the accelerator (
Connected to barrel. A throttle switch 19 is connected to the flow valve 18, and the throttle switch 19 is connected to the electronic control unit 14. The throttle switch 19 is turned on, for example, when the throttle valve 18 is in the idling position, and this on signal is sent to the electronic control unit 14. Air flow meter 1
Reference numeral 7 has a measuring plate 20 that rotates according to intake air -¥kK, and the amount of rotation of this measuring plate 20 is converted into voltage. this.

The voltage is proportional to the amount of intake air, and the voltage proportional to the amount of intake air is sent to the electronic control unit 14. Further, a rotation speed sensor 21 is connected to the electronic control unit 14 to detect the rotation speed of the engine crankshaft. On the other hand, a lean sensor 22 is attached to the exhaust manifold 13, and this lean sensor 22 is connected to the electronic control unit 14. As shown in FIG. 2, the lean sensor 22Fi includes a cup-shaped oxygen ion conductive solid material ff23 made of norconia, and a porous ceramic 24 that covers the outer peripheral surface of the cup-shaped oxygen ion conductive solid ff23, for example, as shown in FIG. placed in the 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 solid electrolyte 23, respectively, and a voltage is applied between the lead wires 25i26 connected to these platinum thin films. Ru. Oxygen molecules in the exhaust gas pass through the porous ceramic 24 by diffusion and reach the cathode platinum thin film of the oxygen ion conductive solid electrolyte 23, where the oxygen molecules endowed with electrons become oxygen ion conductive. After passing through the solid electrolyte 23, the electrons come into contact with the anode platinum thin film of the oxygen ion conductive solid electrolyte 23 and emit electrons, thereby generating a current 11.

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 in FIG. 5, it can be seen that the generated current increases as the oxygen concentration increases.

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 flow is known, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder can be detected. As shown in FIG. 5, a current corresponding to the oxygen concentration P is stably generated when the temperature of the oxygen ion conductive solid electrolyte 23 is as high as approximately 700°C. Inside the oxygen ion conductive solid electrolyte 23, the temperature of the oxygen ion conductive solid electrolyte 23 is set to 70°C.
A heater 27 is provided to maintain the temperature above 0°C.

Further, in order to detect the temperature of the oxygen ion conductive solid electrolyte 23, for example, a thermocouple 28 is placed within the oxygen ion conductive solid electrolyte 23.

As shown by the solid line in FIG. 5, there is a certain relationship between the oxygen concentration P in the exhaust gas and the generator flow rate.
When used for a long time, P contained in exhaust gas
, Zn, F., Pb, etc., the diffusion rate and amount of oxygen gas within the porous ceramic 24 change, and thermal deterioration of the platinum thin film causes a change in the oxygen ion conductive solid electrolyte 23 and the platinum thin film at the interface. As the resistance value decreases, the generator flow rate decreases as indicated by the broken line '' in FIG. However, if the relationship ' with the oxygen concentration P of the drifter deviates from the initial relationship K at the time of occurrence 1, the generator fiA will no longer accurately represent the air-fuel ratio ~.

FIG. 3 shows the electronic control unit 14. Referring to FIG. 3, the electronic control unit 14 includes a digital computer, a microprocessor (MPU) 30 that performs various arithmetic operations, and a random access memory (RAM).
31 , a read-only memory (ROM) 32 in which control globules, calculation constants, etc. are stored in advance, an input port 33 , and an output port 35 are interconnected via a bidirectional path 36 . Furthermore, a clock generator 37 for generating various clock signals is provided within the electronic control unit 14. As shown in FIG. 3, the air flow meter 17 is connected to the input port 33 via a buffer 39 and an AD converter 40. As described above, the air flow meter 17 generates an output voltage proportional to the amount of intake air, and this voltage is converted into a corresponding binary number by the AD converter 40, and this binary number is sent to the MPU via the input port 33 and path 35. 30 is input. On the other hand, the throttle switch 19 and the rotation speed sensor 21 are connected to the input port 33 via corresponding buffers 41 and 42, respectively.

As described above, the throttle switch 19 is turned on when the throttle valve 18 is in the idling position.
This on signal is input to the MPU 3 Q via the input/-) 33 and the path 36. The rotation speed sensor 21 generates a pulse every time the crankshaft rotates by a predetermined crank angle.
The signal is input to the MPU 30 via the MPU 30. On the other hand, the lean sensor 22 is connected to the input port 33 via a current-voltage converter 43, an amplifier 44, and an AD converter 45. As described above, this lean sensor 22 generates a current corresponding to the oxygen concentration in the exhaust gas, and this current line current voltage converter 4
3, this voltage is converted into a voltage proportional to the current value, and this voltage is then converted into a corresponding binary number in an AD converter 45, and this binary number is input to the input yje-) 33 and the path 36.
The signal is input to the MPU 30 via the MPU 30.

Output z-) 35 #'i is provided to output data for operating the fuel injection box 15, and this output port 35 receives a binary number from the MPU 30 to the path 36.
written via. Each output terminal of the output port 35 is connected to a corresponding input terminal of the down counter 46. This down counter 46 is provided to convert the binary data written from the MPU 30 into a corresponding time length.
6 starts counting down the data sent from the output port 35 using a clock signal from the clock generator 37, 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 8-R flip-frog 47 is connected to the output terminal of the down counter 46, and the set input terminal S of the S-R flip-frog 47 is connected to the output terminal of the down counter 46.
Connected to 7. This S-R flip-flop 47 is clocked down by the clock signal of the clock generator 37).
It is set at the same time as the start of the down count, and is reset by the down counter 460 count completion signal when the down count is completed. Therefore, the output terminal Q of the S-R flip 70.pu 47 is at a high level while the down count is being performed. Therefore, the down counter 46 of the fuel injector 15 is connected to the fuel injector 15.
It can be seen that it is energized while being pressed.

Next, the operation of the air-fuel ratio control device according to the present invention will be explained with reference to the flowchart shown in FIG. Referring to FIG. 4, first, in step 50, the intake air amount is calculated from the output signal of the air flow meter 17, and then in step 51, a target air-fuel ratio is set. A detailed explanation of the setting of this target air-fuel ratio will be omitted, but for example, this target air-fuel ratio is set to a desired air-fuel ratio according to the engine speed or engine load. However, Jin's target air-fuel ratio is larger than the stoichiometric air-fuel ratio.

Next, in step 52, the basic fuel injection time τ is calculated from the output signal of the rotation speed sensor 21 and from the engine rotation speed and the intake air amount. is calculated. Next, in step 53, based on the relationship shown in FIG. 5 stored in the ROM 32 (in this case, the vertical axis #i is the voltage value converted by the current-voltage converter), Target output voltage value V of the sensor 22. is calculated. Next, in step 54, it is determined whether or not the throttle switch 19 is on based on the output signal of the throttle switch 19. When the throttle switch 19 is on, that is, when the throttle valve 18 is in the idling position, the process proceeds to step 55. In step 55, it is determined from the output signal of the rotation speed sensor 21 whether the engine rotation speed is greater than a preset rotation speed, for example, 1200 r, p, m, and the engine rotation speed is set to a predetermined rotation speed. If it is determined that the number N is larger than the number N, the process proceeds to step 56 and a fuel cut flag is set. Therefore, the fuel cut flag is set when the engine speed is 4 times higher than the set speed N during deceleration operation. On the other hand, Ste! When it is determined in step 54 that the throttle switch 19 is not on, or when it is determined in step 55 that the engine 11 rotational speed is not greater than the set rotational speed N, the process proceeds to step 57 to set the fuel cut flag. Proceed to the lowered ridge step 58,
Therefore, with the fuel cut 7''y gear lowered, the process proceeds to Step F58 when the engine is not in deceleration operation, or even in deceleration operation, when the engine speed is lower than the set rotation speed.Step When the fuel power and the door lug are set in step 56, the process proceeds to step 59, where it is determined whether or not the fuel cut flag has been neglected for a certain period of time, and if the certain period of time has not elapsed since the fuel cut flag was set, the process proceeds to step 60. The fuel injection process I! is carried out at step 59.However, in this case, the fuel injection operation is stopped because the fuel power and the lid are set.On the other hand, after the fuel cut flag is set at step 59, that is, the fuel When it is determined that the injection action has stopped and a certain period of time has elapsed, proceed to Step 1 and proceed to Step 5.
Verify ■1 in the figure with ■, and use the verification result as the correction coefficient α. That is, at this time, since a certain period of time has passed since the Vi fuel injection was stopped, the inside of the exhaust manifold 13 is filled with the atmosphere, and therefore the oxygen concentration inside the exhaust manifold 13 is about 20 degrees. At this time, if the lean sensor 22 maintains its initial characteristics, the output voltage will be V as shown in FIG. , becomes ■. Therefore, in order to calibrate such changes in salmon over time, V is verified by V, and the verification result is used as a correction coefficient α.As will be described later, the decrease in the generated current due to the change over time is calculated by using this correction coefficient α. I am trying to calibrate using it. When the -r correction coefficient α is calculated in step 61, this correction coefficient α is stored at a predetermined address in the RAM 31, and then the process proceeds to step 60. At this time as well, the fuel injection function remains stopped because the fuel power and door lug are erected.

On the other hand, as described above, when the throttle valve 18 is at the idling position, or when the engine speed is lower than the set speed N even though the throttle valve 18 is at the idling position, the fuel power and the toggle flag are adjusted in step 57. After being dropped off, proceed to Step 58. In step 58, the target output voltage value V of the lean sensor 22 is determined. The K correction coefficient α is multiplied, and the multiplication result is set as the target output voltage value V. Therefore, the target output voltage value V obtained in step 58.

indicates the output voltage V corresponding to the target air-fuel ratio when the lean sensor 22 changes over time. Then Ste, f6
2, the current generated by the lean sensor 22;
That is, it is determined whether the output voltage V is larger than the target value V, and the output voltage V of the lean sensor 922 is 4 times larger than the target value v0.
If it is larger, the process proceeds to step 63 where the fuel injection time T becomes the basic injection time τ. is increased by γ. t
When it is determined in step 62 that the output voltage V of the lean sensor 220 is not larger than the target value vo, it is determined in step 64 whether the output voltage V of the lean sensor 22 is smaller than the target value vo. be done. In Step 4, the output voltage ■ of the lean sensor 22 is the target value ■.

When it is determined that the fuel injection time τ is the basic injection time τ in step 65. On the other hand, when it is determined in step 64 that the output voltage of the lean sensor 22 is not smaller than the target value vo, the process proceeds to step 66, where the basic injection time 1 is set to the fuel injection time τ. Ding. can be entered. When the fuel injection time τ is determined in either of the stations 3 and 65° 66, the fuel injection action is performed in the station 7'60 according to this fuel injection time τ. Step 62 to Step 6
6 and FIG. 5, when the air-fuel ratio becomes leaner than the target air-fuel ratio, the amount of fuel is increased, and when the air-fuel ratio becomes richer than the target air-fuel ratio, the amount of fuel is reduced, and thus the air-fuel ratio is controlled to the target air-fuel ratio. I understand that.

As mentioned above, the correction coefficient α can be determined only when the inside of the exhaust manifold 13 is filled with the atmosphere. Therefore, in the present invention, the determination whether or not the inside of the exhaust manifold 13 is filled with the atmosphere is performed. Equipment must be provided. In the embodiment described above, this discrimination device consists of a throttle switch 19 and a rotational speed sensor 21, and uses the fact that the fuel injection action is stopped when the vehicle decelerates to determine the correction coefficient α.

On the other hand, since the inside of the exhaust manifold 13 is filled with atmosphere even before starting the aircraft, the correction coefficient α can be determined at this time. That is, in this case, the ignition switch 70 is connected to the input port 33 via the buffer 71 as shown in the broken line frame in FIG.
72 is connected to the input port 33 via a buffer 73 and an AD converter 74. The temperature sensor 72 consists of a thermocouple 28 as shown in FIG. 2, and the heater 27 shown in FIG. 2 is heated when the ignition switch 70 is turned on. Therefore, the temperature of the oxygen ion conductive solid electrolyte 23 is approximately 700°C due to the heating action of the heater 27.
Moreover, it may be determined from the output signal of the rotation speed sensor 21 that the engine rotation speed is zero, and the correction coefficient α may be determined at this time.

As described above, according to the present invention, it is possible to calibrate fluctuations in the generated current due to changes in the lean sensor over time before starting the aircraft or each time the engine is decelerating.

Therefore, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder can always be accurately 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 side sectional view of a lean sensor, FIG. 3 is a circuit diagram of an electronic control unit, and FIG. 4 is an operation of an air-fuel ratio control device according to the present invention. Flow chart showing the lean sensor occurrence 1 in Figure 5.
FIG. 11 is a diagram showing the relationship between flow and oxygen concentration. 13... Exhaust manifold, 14... Electronic control unit, 15... Fuel injection valve, 17... Air flow meter, 18-... Throttle valve, 19... Throttle switch, ・22... Lean sensor. Figure 5 V m

Claims (1)

[Claims] A lean sensor that generates an output signal proportional to the oxygen concentration in the exhaust passage is installed in the engine exhaust passage, and the nuclear lean sensor is connected to an electronic control unit, and the electronic control unit outputs the output signal of the lean sensor and the oxygen concentration. In the air-fuel ratio control device, the air-fuel ratio control device is provided with a storage means that stores the relationship between the above-mentioned A lean sensor that includes a discriminating device for discriminating whether or not the engine exhaust passage is filled with the atmosphere, and is stored in the storage means when the engine exhaust passage is filled with the atmosphere in response to the discriminating device. An air-fuel ratio control device for an internal combustion engine, wherein the electronic control unit is provided with a calibration means for calibrating the relationship between the output signal and the oxygen concentration.