JPH0217705B2 - - 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 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. 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 contained in the exhaust gas , due to adhesion of Zn, Fe, Pb, etc. and physical destruction due to thermal shock, which changes the diffusion rate and amount of oxygen gas within the porous ceramic layer covering the outer peripheral surface of the zirconia plate. Even at the same oxygen concentration, the current value gradually increases or decreases over time. 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 an air-fuel ratio system 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. An object of the present invention is to provide a fuel ratio control device.

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 the atmosphere via an intake pipe 16, an air flow meter 17, and an air cleaner (not shown). A throttle valve 18 is disposed within the intake pipe 16, and the throttle valve 18 is connected to an accelerator pedal provided in the driver's cab of the vehicle. A throttle switch 19 is connected to the throttle 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 17
has a measuring plate 20 that rotates according to the amount of intake air, and the amount of rotation of this measuring plate 20 is converted into voltage. This voltage is proportional to the amount of intake air, and the voltage proportional to the amount of intake air is the voltage proportional to the amount of intake air.
Sent to 4. Furthermore, the electronic control unit 14
A rotation speed sensor 21 is connected 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 22 includes, for example, a cup-shaped oxygen ion conductive solid electrolyte 23 made of zirconia, and a porous ceramic 24 covering the outer peripheral surface of the cup-shaped solid electrolyte 23. placed inside. 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 25 and 26 connected to these platinum thin films. applied. 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 pass through the oxygen ion conductive solid electrolyte 23. After passing through the oxygen ion conductive solid electrolyte 23, the electrons contact the platinum thin film for the anode of the oxygen ion conductive solid electrolyte 23 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 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 current is known, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder can be detected. As shown in FIG. 5, the current that corresponds to the oxygen concentration P is stably generated when the temperature of the oxygen ion conductive solid electrolyte 23 becomes higher than approximately 700°C. A heater 27 is provided inside the oxygen ion conductive solid electrolyte 23 to maintain the temperature of the oxygen ion conductive solid electrolyte 23 at 700° C. or higher. Further, in order to detect the temperature of the oxygen ion conductive solid electrolyte 23, for example, a thermocouple 28 is connected to the oxygen ion conductive solid electrolyte 23.
Located within 3.

As shown by the solid line K in FIG. 5, there is a certain relationship between the oxygen concentration P in the exhaust gas and the generated current A, but if the lean sensor 22 is used for a long time, the P, Zn, and Due to the adhesion of Fe, Pb, etc., the diffusion rate and amount of oxygen gas in the porous ceramic 24 change, and due to thermal deterioration of the platinum thin film, the resistance value at the interface between the oxygen ion conductive solid electrolyte 23 and the platinum thin film decreases. As a result, the generated current A decreases as shown by the broken line K' in FIG. However, if the relationship K' between the generated current A and the oxygen concentration P deviates from the initial relationship K, the generated current A will no longer accurately represent the air-fuel ratio A/F.

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 35 are interconnected via a bidirectional bus 36. Furthermore, within the electronic control unit 14 is a clock generator 3 that generates various clock signals.
7 is provided. 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 via the input port 33 and the bus 35.
Input to MPU30. 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, and this on signal is input to the MPU 30 via the input port 33 and the bus 36. The rotation speed sensor 21 generates a pulse every time the crankshaft rotates by a predetermined crank angle,
This pulse is input to the MPU 30 via the input port 33 and the bus 36. On the other hand, the lean sensor 22 includes a current-voltage converter 43, an amplifier 44, and
It is connected to the input port 33 via the AD converter 45. As described above, this lean sensor 22 generates a current corresponding to the oxygen concentration in the exhaust gas, this current is converted into a voltage proportional to the current value in the current-voltage converter 43, and then this voltage is converted to The binary numbers are converted into corresponding binary numbers at the input port 33 and the bus 36, and the binary numbers are input to the MPU 30 via the input port 33 and the bus 36.

The output port 35 is provided to output data for operating the fuel injection valve 15, and this output port 35 is provided with binary data to the MPU 3.
0 via bus 36. 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 the corresponding time length.
starts counting down the data sent from the output port 35 in response to the 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 S-R flip-flop 47 is connected to the output terminal of the down counter 46, and the set input terminal S of the S-R flip-flop 47 is connected to the clock generator 37. This S-R flip-flop 47 is connected to the clock generator 3.
It is set at the same time as the down count starts by the clock signal 7, and is reset by the count completion signal of the down count 46 when the down count is completed. Therefore, the output terminal Q of the S-R flip-flop 47 is at a high level while the down count is being performed. The output terminal Q of the S-R flip-flop 47 is connected to the fuel injection valve 15 via a power amplification circuit 48, and therefore the fuel injection valve 15 is connected to the output terminal Q of the S-R flip-flop 47.
It can be seen that the down counter 46 is energized while down-cutting.

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 Figure 4, first, step 5.
At step 0, the intake air amount is calculated from the output signal of the air flow meter 17, and then at 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 desirable air-fuel ratio according to the engine speed or engine load. However, this target air-fuel ratio is larger than the stoichiometric air-fuel ratio.
Next, in step 52, the engine speed and intake air amount calculated from the output signal of the speed sensor 21 are calculated.
The basic fuel injection time τ _p is calculated in . Next, in step 53, the relationship shown in FIG. 5 stored in the ROM 32 is determined (however, in this case, the vertical axis is the voltage value V converted by the current-voltage converter).
From this, a target output voltage value V _p of the lean sensor 22 corresponding to the target air-fuel ratio is calculated. Next, in step 54, it is determined from the output signal of the throttle switch 19 whether or not the throttle switch 19 is on, and 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. If it is determined that the fuel cut flag is larger than the fuel cut flag, the process proceeds to step 56 and a fuel cut flag is set. Therefore, the fuel cut flag is set during deceleration operation in which the engine speed is higher than the set rotation speed N. On the other hand, if it is determined in step 54 that the throttle switch 19 is not on, or if it is determined in step 55 that the engine speed is not greater than the set rotation speed N, the process proceeds to step 57 and the fuel cut flag is lowered. The process then proceeds to step 58. Therefore, the process proceeds to step 58 with the fuel cut flag lowered when the engine is not in deceleration operation, or when the engine speed is lower than the set rotation speed N even in deceleration operation. When the fuel cut flag is set in step 56, the process proceeds to step 59, where it is determined whether or not a certain period of time has elapsed.If the certain period of time has not elapsed since the fuel cut flag was set, the process proceeds to step 60, where fuel injection processing is performed. It is done. However, in this case, since the fuel cut flag is set, the fuel injection action is stopped. on the other hand,
After the fuel cut flag is set in step 59, that is, when it is determined that a certain period of time has elapsed since the fuel injection action was stopped, the process proceeds to step 61, where _Vs in FIG. 5 is divided by _Va , and The subtraction result is set as the correction coefficient α. That is, at this time, since a certain period of time has passed since the fuel injection was stopped, the inside of the exhaust manifold 13 is filled with the atmosphere.
Therefore, the oxygen concentration within the exhaust manifold 13 is approximately 20%. At this time, the lean sensor 22
If the lean sensor 22 maintains its initial characteristics, the output voltage will be V _a in FIG. 5, and on the other hand, if the lean sensor 22 has deteriorated due to changes over time, the output voltage will be V _s in FIG. Therefore, in order to calibrate such changes over time, V _s is divided by V _a and the result of the division is used as a correction coefficient α. I try to calibrate using α. Step 6
When the correction coefficient α is calculated in step 1, the correction coefficient α is stored at a predetermined address in the RAM 31, and then the process proceeds to step 60. Since the fuel cut flag is also set at this time, the combustion injection action remains stopped.

On the other hand, as mentioned above, when the throttle valve 18 is not in the idling position or when the throttle valve 1
If the engine rotation speed is lower than the set rotation speed N even when the engine 8 is in the idling position, the fuel cut flag is lowered in step 57, and then the process proceeds to step 5.
Proceed to step 8. In step 58, the target output voltage value V _p of the lean sensor 22 is multiplied by the correction coefficient α, and the multiplication result is set as the target output voltage value V _p . Therefore, the target output voltage value obtained in step 58
V _p indicates the output voltage V corresponding to the target air-fuel ratio when the lean sensor 22 changes over time.
Next, in step 62, the current currently generated by the lean sensor 22, that is, the output voltage V, is set to the target value.
It is determined whether the output voltage V of the lean sensor 22 is larger than the target value V p, and if the output voltage V of the lean sensor 22 is larger than the target value V _p , the process proceeds to step 63 _, where the fuel injection time τ is increased by γ with respect to the basic injection time τ _p. . Further, when it is determined in step 62 that the output voltage V of the lean sensor 22 is not larger than the target value _Vp , the output voltage V of the lean sensor 22 is determined in step 64.
It is determined whether the output voltage V of No. 2 is smaller than the target value V _p . When it is determined in step 64 that the output voltage V of the lean sensor 22 is smaller than the target value V _p , in step 65 the fuel injection time τ is decreased by β with respect to the basic injection time τ _p ; When it is determined that the output voltage V of the sensor 22 is not smaller than the target value V _p , the routine proceeds to step 66, where the basic injection time τ _p is entered into the fuel injection time τ. When the fuel injection time τ is determined in any one of steps 63, 65, and 66, a fuel injection operation is performed in step 60 according to the fuel injection time τ. Steps 62 to 66 and the fifth step
It can be seen from the figure that 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.

As mentioned above, the correction coefficient α can be determined when the inside of the exhaust manifold 13 is filled with the atmosphere.
It is necessary to provide a discriminating device for determining whether or not the inside of the chamber 3 is filled with atmosphere. In the embodiments described so far, this discrimination device is the throttle switch 19.
and a rotational speed sensor 21, and the correction coefficient α is determined by utilizing the fact that the fuel injection action is stopped when the vehicle decelerates.

On the other hand, even before the engine starts, the exhaust manifold 1
3 is filled with air, so 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. Connect to input port 33. The temperature sensor 72 comprises a thermocouple 28, an example of which is shown in FIG. 2, and the heater 27 shown in FIG. 2 is heated when the ignition switch 70 is turned on. Therefore, the ignition switch 70 is turned on, and the heater 2 is turned on.
The temperature of the oxygen ion conductive solid electrolyte 23 becomes higher than approximately 700°C due to the heating action of step 7, and it is determined from the output signal of the rotation speed sensor 21 that the engine rotation speed is zero, and the correction is made at this time. The coefficient α may also be determined.

As described above, according to the present invention, fluctuations in the current generated due to changes in the lean sensor over time can be detected before starting the engine.
Alternatively, it can be calibrated every time the deceleration operation starts. 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 the lean sensor, Fig. 3 is a circuit diagram of the electronic control unit, Fig. 4 is a flowchart showing the operation of the air-fuel ratio control device according to the present invention, and Fig. 5 is a diagram showing the current generated by the lean sensor. It is a figure showing the relationship of 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.

Claims (1)

[Claims] 1. 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 lean sensor is connected to an electronic control unit, and the electronic control unit compares the output signal of the lean sensor with the oxygen concentration. In the air-fuel ratio control device, the air-fuel ratio control device is equipped with a storage means that stores the relationship between A determination device is provided for determining whether or not the exhaust passage is filled with the atmosphere, and in response to the determination device, the output of the lean sensor is stored in the storage means when the engine exhaust passage is filled with the atmosphere. 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 signal and the oxygen concentration.