JP2005171924A - Air-fuel ratio control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air fuel ratio control system capable of preventing occurrence of misfire and engine stall by performing control with considering instability at a time of engine start and instability due to change of control style. <P>SOLUTION: In an air fuel ratio control system controlling air fuel ratio of mixture based on measured value of the air fuel ratio sensor 50, fuel injection valve operation speed is delayed if air fuel ratio control is started within a predetermined period of time after the air fuel ratio sensor 50 becomes capable of measuring. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an air-fuel ratio control system for controlling an air-fuel ratio of an air-fuel mixture based on a measured value of an air-fuel ratio sensor.

Conventionally, for example, the output of the air-fuel ratio sensor (that is, the IP value is the output current value of the air-fuel ratio sensor) according to the engine load, such as GHP (Gas Heat Pump), and the rotational speed. There is an air-fuel ratio control system that performs air-fuel ratio control by operating a fuel control valve so that a measured IP value becomes a target IP value stored in advance in an ECU (Electronic Control Unit).
In such an air-fuel ratio control system, when the ECU adjusts the opening of the fuel control valve according to the output of the air-fuel ratio sensor, the valve operating speed is always controlled at the same speed.
For example, when the oxygen concentration is determined to be high by the output of the air-fuel ratio sensor, the fuel control valve is opened to make the air-fuel mixture rich, while the oxygen concentration is determined to be low Performs the operation of closing the fuel control valve to make the mixture lean.
As an example of a technique related to such an air-fuel ratio control system, there is one as shown in Patent Document 1 below.

Japanese Patent Laid-Open No. 5-33728

By the way, for example, when the engine is started, the control mode may change from engine start control to air-fuel ratio control during normal operation.
For example, at the time of engine start control or the like, the air-fuel ratio is controlled to be richer in order to surely start the engine. Therefore, when switching to air-fuel ratio control of normal operation, the exhaust of NOx or the like is suppressed so as to be suppressed. Reduce the fuel ratio.
In this case, specifically, a process of closing the fuel control valve from the opened state is performed.
However, immediately after starting the engine as described above, generally, when the operation of closing the fuel control valve as described above is performed due to the instability of the engine and instability by changing the control mode, Sometimes the air-fuel ratio becomes too lean, causing a misfire and stopping.
This is because the speed of the closing operation of the fuel control valve is too fast, and the air-fuel ratio becomes lean before the misfire avoidance control for preventing the misfire of the engine is activated, and this case can be avoided. could not.
In addition, when the measured value of the air-fuel ratio sensor fluctuates for some reason, there is no way to verify whether or not an abnormality has occurred in the air-fuel ratio sensor, resulting in misfire or engine stall, Since the air-fuel ratio sensor cannot be stably activated, there have been cases where misfires and engine stalls occur due to erroneous measurement.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to perform control that takes into account instability at engine startup and instability by changing the control mode. To provide an air-fuel ratio control system capable of preventing misfire and engine stall.
In addition, by verifying that the air-fuel ratio sensor is not abnormal based on the measured values and rotation speed of the air-fuel ratio sensor, misfires and engine stalls are prevented and the air-fuel ratio sensor is stably activated. An air-fuel ratio control system is provided.

  The problems to be solved by the present invention are as described above. Next, means for solving the problems will be described.

In claim 1, in the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
When air-fuel ratio control is started within a predetermined time after the air-fuel ratio sensor becomes measurable,
The air-fuel ratio control system is characterized in that the operating speed of the fuel control valve is reduced.

According to claim 2, in the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
When air-fuel ratio control is started after a predetermined time has elapsed since the air-fuel ratio sensor can be measured,
The air-fuel ratio control system is configured to slow down the closing operation speed in the closing operation of the fuel control valve.

According to claim 3, in the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
When air-fuel ratio control is started after a predetermined time has elapsed since the air-fuel ratio sensor can be measured,
The air-fuel ratio control system is characterized in that the opening operation speed in the opening operation of the fuel control valve is increased.

In claim 4, in the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
When the measured value of the air-fuel ratio sensor is smaller than a predetermined threshold value and the engine is stopped,
The air-fuel ratio control system is configured to check the operation of the air-fuel ratio sensor.

In claim 5, when it is determined as abnormal in the operation check of the air-fuel ratio sensor,
The engine is configured as an air-fuel ratio control system in which the engine is operated for a predetermined time by control without using the air-fuel ratio sensor and the operation of the air-fuel ratio sensor is confirmed again.

In the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measurement value of the air-fuel ratio sensor,
When the measured value of the air-fuel ratio sensor is smaller than a predetermined threshold and the engine speed deviation is smaller than a predetermined threshold,
An air-fuel ratio control system is characterized in that the engine is operated for a predetermined time by control without using the air-fuel ratio sensor and the operation of the air-fuel ratio sensor is checked again.

In claim 7, in the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
A substantially cylindrical protector for protecting the element portion of the air-fuel ratio sensor is provided,
Form a bridge across the diameter direction at the tip of the protector,
The width of the bridge is larger than the outer shape of the element portion of the air-fuel ratio sensor,
A gap is formed between the bridge and the element portion of the air-fuel ratio sensor, and the air-fuel ratio control system is configured.

  According to an eighth aspect of the present invention, the bridge of the protector is configured as an air-fuel ratio control system that is attached to an exhaust passage such as an exhaust manifold so as to be perpendicular to the flow of exhaust.

  According to a ninth aspect of the present invention, the lower end portion of the cylindrical side surface of the protector is configured as an air-fuel ratio control system formed so as to cover the vent of the element portion of the air-fuel ratio sensor.

  As effects of the present invention, the following effects can be obtained.

  According to the configuration of the first aspect, it is possible to prevent engine misfire or engine stall (engine stop) in a transient state in which the operating state shifts from a starting state of the engine to a steady state in which air-fuel ratio control is started.

  According to the configuration of claim 2, in the transient state where the operating state shifts from the engine starting state to the steady state in which the air-fuel ratio control is started, the fuel supply valve is suddenly reduced to cause a misfire. It is possible to prevent the occurrence of an engine stall or the like due to a misfire before the process by the avoidance control is executed.

  According to the configuration of the third aspect, the fuel control valve can be quickly opened when the fuel control valve needs to be opened in a transient state in which the operation state shifts from the engine starting state to the steady state in which the air-fuel ratio control is started. This makes it possible to quickly supply the necessary fuel, thus preventing misfires and engine stalls.

  According to the configuration of the fourth aspect, when the measurement result of the air-fuel ratio sensor indicates that the result is rich, the result indicates that the air-fuel ratio sensor itself is not abnormal or the air-fuel ratio sensor 50 is abnormal. It is possible to verify that this has occurred.

According to the configuration of the fifth aspect, even if some abnormality occurs in the air-fuel ratio sensor, if the oil component is simply attached to the air-fuel ratio sensor, the engine is not used for a predetermined time without using the air-fuel ratio sensor. Is operated, the oil adhering to the air-fuel ratio sensor can be evaporated or incinerated by the heater of the air-fuel ratio sensor and exhaust heat.
As a result, the cause of the measurement abnormality of the air-fuel ratio sensor due to the adhering oil is removed, and the control using the air-fuel ratio sensor can be performed again.

According to the configuration of the sixth aspect, even when oil or the like adheres to the air-fuel ratio sensor and temporarily shows richness, the oil attached to the air-fuel ratio sensor 50 is evaporated or incinerated in the same manner as described above. As a result, it is possible to return the air-fuel ratio sensor to a normal state and perform air-fuel ratio control again.
In other words, even when oil is attached to the air-fuel ratio sensor and the air-fuel ratio sensor temporarily performs erroneous measurement, the engine can be operated in a normal state.

  According to the seventh aspect of the present invention, since overcooling due to ventilation of exhaust gas can be prevented, the heat retention of the air-fuel ratio sensor can be improved and stable measurement can be performed.

  According to the configuration of the eighth aspect, the duty ratio can be reduced, the heat retaining property of the air-fuel ratio sensor can be improved, and the amount of electric power used for the heater can be suppressed. It can be activated and accurately measured.

  According to the configuration of the ninth aspect, it is possible to prevent the oil component or the condensed water in the exhaust gas from adhering to the tip portion of the air-fuel ratio sensor, and to prevent the air-fuel ratio sensor from deteriorating or malfunctioning.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the accompanying drawings for understanding of the present invention. The following best mode for carrying out the present invention is an example embodying the present invention, and is not intended to limit the technical scope of the present invention.
1 is a schematic configuration diagram of an air-fuel ratio control system according to an embodiment of the present invention, FIG. 2 is a flowchart showing an example of a series of processes performed by the air-fuel ratio control system, and FIG. 3 is a series of processes performed by the air-fuel ratio control system FIG. 4 is an external view when an air-fuel ratio sensor (dotted line portion) is attached to the protector (solid line portion), FIG. 5 is an external view of the protector, and FIG. 6 is a heater provided in the air-fuel ratio sensor. It is the graph which showed the duty ratio in the case of heating.

First, the schematic configuration of the air-fuel ratio control system according to the best mode for carrying out the present invention will be described with reference to FIG.
Further, the air-fuel ratio control system described below may be a gas engine such as GHP (Gas Heat Pump), which may be a gasoline engine, and this case will be described as a specific example.
First, the mixer 20 that generates air-fuel mixture by mixing air (outside air) taken from the air cleaner 30 and fuel such as gas will be described.
The mixer 20 is mainly configured to mainly include a venturi 23, a fuel control valve 22, a fixed valve 21, a fuel increase valve 27, and a throttle valve 25.
The piston 45 of the engine 60 is lowered and the pressure in the cylinder (combustion chamber) 40 becomes negative. Air is taken in from the air cleaner 30 through the venturi 23.
The venturi 23 has a narrow air passage, a fuel supply passage is communicated with the narrow portion, and a portion of the air flow where the flow of air is fast sucks fuel from the fuel supply passage using negative pressure. To produce a mixture.
The amount of fuel supplied to the venturi 23 is adjusted by the fuel control valve 22.
Specifically, the amount of the fuel is adjusted by controlling a solenoid as an actuator for driving the valve body of the fuel control valve 22 by an ECU 10 (electronic control unit) which is an example of a control unit.
As shown in FIG. 1, as a system for supplying fuel to the venturi 23, there is a system that passes through the fixed valve 21 in addition to the system that passes through the fuel control valve 22.
The fixed valve 21 is for supplying only a predetermined amount of fuel to the venturi 23, and is set according to the type of fuel.
Therefore, the valve of the fixed valve 21 is not controlled by the ECU 10 or the like, but is only adjusted in advance during maintenance such as when the mixer 20 is manufactured or installed, and is fixed at a constant opening during operation. .
That is, the ECU 10 controls the fuel control valve 22 so that the air-fuel ratio in the air-fuel mixture generated by the venturi 23 can be changed.
The air-fuel mixture generated in this way reaches the throttle valve 25, and the flow rate of the air-fuel mixture passing through the throttle valve 25 varies depending on the opening degree of the throttle valve 25.
Specifically, the opening degree of the valve body of the throttle valve 25 is changed by driving a stepping motor as an actuator. The stepping motor is controlled by the ECU 10, and the mixing that passes when the opening degree of the throttle valve 25 is opened. The flow rate of the air-fuel mixture increases while the flow rate of the air-fuel mixture passing therethrough decreases.

Further, the fuel increase valve 27 may be provided downstream of the throttle valve 25 (engine 60 side).
The function of the fuel increase valve 27 is opened when only the fuel supplied from the fuel control valve 22 is insufficient for the fuel contained in the air-fuel mixture.
Specifically, when the opening degree of the throttle valve 25 (throttle opening degree) is close to full open, etc., it operates particularly when it is desired to make the air-fuel ratio of the air-fuel mixture rich. In a control state that cannot be completely compensated for by the control valve, supplementary assistance is provided.
That is, the fuel increase valve 27 shown in FIG. 1 is not necessarily a necessary component for the air-fuel ratio control system of the present invention, but FIG. 1 shows an example in which the fuel increase valve 27 is provided. Therefore, in the following description, it is assumed that the fuel increase valve 27 is not provided.

Further, the air-fuel mixture that has passed through the throttle valve 25 is sucked into the cylinder 40 of the engine 60 through the suction valve 41, compressed by the piston 45 with the suction valve 41 and the exhaust valve 42 closed, and then by the spark plug 43. Explodes on ignition.
The crankshaft is rotated by the raising and lowering of the piston 45, and the rotation angle and the rotation speed are detected by the rotation speed sensor 44 and input to the ECU 10.
The exhaust gas after the explosion is discharged through the exhaust valve 42.
At this time, the air-fuel ratio sensor 50 measures the air-fuel ratio (generally oxygen) in the exhaust gas, and is provided in an exhaust passage such as an exhaust manifold. The ECU 10 is based on the detection result of the air-fuel ratio sensor 50. The air / fuel ratio of the air-fuel mixture sucked into the cylinder 40 can be calculated.
Specifically, a measured value (output) that is a result of measurement by the air-fuel ratio sensor 50 is output as a current magnitude (hereinafter simply referred to as “IP value”), and this IP value is the ECU 10. Will be entered.
Further, the air-fuel ratio sensor 50 described here outputs IP as a larger value as the amount of oxygen contained in the exhaust gas is larger, while the IP value is smaller as the amount of oxygen contained in the exhaust gas is smaller. It shall have the characteristic to be output.
That is, the IP value is proportional to the actual air-fuel ratio of the air-fuel mixture.
Therefore, the ECU 10 controls the fuel so that the IP value measured by the air-fuel ratio sensor 50 becomes the target IP value stored in advance in the ECU 10 so that the actual air-fuel ratio of the air-fuel mixture becomes the target air-fuel ratio. The valve 22 and the throttle valve 25 are controlled.
The target IP value is stored in advance as a map in the storage means (for example, ROM) of the ECU 10 in association with the engine speed and load detected by the engine speed sensor 44.
In addition, since the air-fuel ratio sensor 50 needs to be activated by setting the temperature of the element itself to a certain temperature when measurement is started, the air-fuel ratio sensor 50 is heated by a heater or the like so that the temperature is reached.
The temperature in this case is also controlled by the ECU 10 or the like.

Next, a series of processes performed by the air-fuel ratio control system configured as described above will be described with reference to FIG.
First, the ECU 10 starts up the engine 60 (S10) and warms up the heater by energizing the heater so that the air-fuel ratio sensor 50 can be measured (S20).
Then, the ECU 10 determines whether or not a predetermined time (in this case, for example, 10 seconds) or more has elapsed since the air-fuel ratio sensor can be measured by the warm-up (S30).
In step S30, when normal air-fuel ratio control is started using the measurement result of the air-fuel ratio sensor 50 without the predetermined time (that is, within the predetermined time), fuel control is performed. In order to slow down the operating speed of the valve 22, the control constant is reduced (S51), and the above-described processing is repeated.
That is, in step S51, specifically, the control constant of the stepping motor for operating the fuel control valve 22 is reduced.
For example, if the rated control constant when performing normal air-fuel ratio control is P = 0.01, the control constant is changed to a small value such as P = 0.001.
By such processing, in the transient state where the operating state shifts from the engine starting state to the steady state where the air-fuel ratio control is started, the influence of the abnormality of the IP value due to the abnormality of the air-fuel ratio sensor that is likely to occur immediately after the starting is reduced. Engine misfire and engine stall (engine stop) can be prevented.
As a specific example of the abnormality of the air-fuel ratio sensor and the symptom thereof, for example, the output increases due to cracks in the element portion of the air-fuel ratio sensor, or the output decreases due to adhesion of lubricating oil or the like to the element portion of the air-fuel ratio sensor. The output of the air-fuel ratio sensor is clogged, or the output is reduced due to deterioration of the air-fuel ratio sensor.

Next, after the predetermined time has elapsed in step S30, normal air-fuel ratio control is started using the measurement result of the air-fuel ratio sensor 50, and the fuel control valve 22 ("GVM" in FIG. When the notation is closed (S40), the ECU 10 decreases the control constant to slow down the closing operation speed of the fuel control valve 22 (S52).
In the case of this step S52, the control constant in the case of closing the fuel control valve 22 is made slightly different from the case of the above step S51.
In this case, for example, when the rated control constant in the case of performing normal air-fuel ratio control is P = 0.01, the control constant is changed to a small value such as P = 0.005.
By such a process, in the transient state where the operating state shifts from the engine starting state to the steady state where the air-fuel ratio control is started, the fuel supply valve abruptly decreases by closing the fuel control valve 22, thereby misfiring. It is possible to prevent the occurrence of an engine stall or the like due to a misfire before the process by the avoidance control is executed.
Subsequently, the ECU 10 acquires the rotation speed of the crankshaft from the rotation speed sensor 44, thereby measuring the rotation speed of the engine 60 and calculating a rotation speed deviation from the target rotation speed stored in the ECU 10 in advance (S60). ).
Then, ECU 10 determines whether or not the rotational speed deviation calculated in step S60 is equal to or greater than a threshold value stored in ECU 10 in advance (S70).
If it is determined in step S70 that the rotational speed deviation (difference between the maximum value and the minimum value of the rotational speed at a specific time) is greater than or equal to the threshold value, the state of the engine 60 is still unstable. Repeat (takes the path “Y” in S70 of FIG. 2).
On the other hand, if it is determined in step S70 that the rotational speed deviation is not greater than or equal to the threshold value, processing such as resetting the control constant related to integration, which is the accumulation of control from the past, is performed to optimize the control constant. (S80), the above process is repeated.

Next, when the fuel control valve 22 opens in the process of step S40, the ECU 10 increases the control constant in order to increase the speed of opening the fuel control valve 22 (S53).
In this case, for example, when the rated control constant in the case of performing normal air-fuel ratio control is P = 0.01, the control constant is changed to a large value such as P = 0.025.
By such processing, the fuel control valve 22 is quickly opened when it is necessary to open the fuel control valve 22 in a transient state where the operating state shifts from the engine starting state to the steady state where air-fuel ratio control is started. This makes it possible to supply the necessary fuel quickly, thus preventing misfires and engine stalls. For example, this may be the case when the load increases and a large amount of fuel is supplied.

By the way, the exhaust gas contains an oil component, and when such an oil component temporarily adheres to the air-fuel ratio sensor 50, the air-fuel mixture is rich based on the measured value of the air-fuel ratio sensor 50. There is a case where it is judged incorrectly.
In such a case, even if the oil component adheres to the air-fuel ratio sensor 50, by operating for a certain time, the adhered oil component evaporates or is not incinerated by the heat of the heater or the exhaust heat. It is known that the air-fuel ratio sensor 50 starts measuring normally again.
However, conventionally, when the air-fuel ratio sensor 50 shows an erroneous measurement value due to the adhesion of oil or the like, the air-fuel mixture becomes lean because control such as rich avoidance air-fuel ratio control is immediately performed. As a result, there was a case where a misfire resulted and the engine stalled.
Therefore, in the following, when it is shown that the air-fuel ratio sensor 50 is rich, even if the cause is due to the adhesion of oil, the air-fuel ratio control system is operated normally and the cause is verified. An example will be described with reference to FIG.
The ECU 10 starts up the engine 60 (S110) and warms up the heater by energizing the heater so that the air-fuel ratio sensor 50 can be measured (S120).
Then, the ECU 10 determines the concentration of the air-fuel ratio of the air-fuel mixture by determining whether or not the IP value that is the measured value of the air-fuel ratio sensor 50 is equal to or less than a predetermined value (S125).
In step S125, it is determined whether or not the IP value that is the measured value of the air-fuel ratio is a value smaller than 0.1 mA.
In the above case, it is assumed that the air-fuel ratio is in an ideal state when the IP value is a predetermined value (for example, 0.1 mA). Therefore, in step S125, the air-fuel ratio is either rich or lean. Judging whether there is.
In this case, if the IP value is smaller than 0.1 mA, the air-fuel ratio is rich. On the other hand, if the IP value is larger than 0.1 mA, the air-fuel ratio is lean. Judge that there is.
If it is determined by this determination that the air-fuel ratio is lean, the above process is repeated.
On the other hand, if it is determined in the above determination that the air-fuel ratio is rich, the ECU 10 starts rich avoidance air-fuel ratio control for avoiding a state where the air-fuel ratio is rich (S130), and the fuel control valve A closing operation is executed so as to close 22 (S140).
Further, the ECU 10 measures the rotational speed of the engine 60 from the measurement result of the rotational speed sensor 44, calculates a rotational speed deviation from the target rotational speed stored in the ECU 10 in advance, and the rotational speed deviation is stored in the ECU 10 in advance. It is determined whether or not the threshold is equal to or greater than the threshold value (S145).
This threshold value is stored in the storage means as a map.
In the determination of step S145, (1) if the rotational speed deviation is not greater than or equal to the threshold, the process proceeds to step S230. (2) If the rotational speed deviation is greater than or equal to the threshold, the process proceeds to step S150. ) If the engine 60 is stopped and not rotating, the process proceeds to step S210.

The case (3) will be described.
The ECU 10 checks the operation of the air-fuel ratio sensor when the measured value of the air-fuel ratio sensor 50 is smaller than a predetermined threshold value (result of step S125) and the engine is stopped (result of step S145). The mode is set (S210).
Specifically, in the operation confirmation in step S210, the output of the air-fuel ratio sensor 50 is measured when the engine 60 is simply idled using a cell motor or the like without supplying the air-fuel mixture to the engine 60.
As a result of the measurement in step S210, what is measured by the air-fuel ratio sensor 50 when the engine 60 is not started is originally a general atmospheric oxygen concentration (about 20%) on the ground.
However, at this time, if oil or the like is attached to the air-fuel ratio sensor 50, the operation is confirmed using the characteristic that the oxygen concentration in the atmosphere cannot be accurately measured (S220).
Specifically, in this step S220, if the measured value (IP value) of the air-fuel ratio sensor 50 is 0.7 (normal value when a general atmospheric oxygen concentration is measured) or more, the air-fuel ratio sensor. Since a situation has occurred in which the engine 60 stops despite the fact that the engine 50 operates normally, the process proceeds to a process (after step S160) for checking whether or not a part other than the air-fuel ratio sensor 50 has failed.
On the other hand, in step S220, if the IP value is 0.7 or less, it can be determined that the air-fuel ratio sensor 50 is not operating normally and is abnormal. The process shifts to a process (step S230 and subsequent steps) for determining whether it is in a situation where it is attached and cannot be normally measured.
By this processing, when the measurement result of the air-fuel ratio sensor 50 indicates that the air-fuel ratio sensor 50 is rich in step S125, the result is that the air-fuel ratio sensor 50 itself is not abnormal, or conversely It is possible to verify that an abnormality has occurred in the sensor 50.

Here, a case where the process proceeds to step S230 in step S220 will be described.
Hereinafter, when it is determined that the air-fuel ratio sensor 50 is in an abnormal state by the above-described processing, the engine 60 is operated for a predetermined time by control without using the air-fuel ratio sensor 50, and the air-fuel ratio sensor 50 is again operated. A process for confirming the operation will be described.
If it is determined in step S220 that an abnormality has occurred in the air-fuel ratio sensor 50, the ECU 10 controls the engine 60 in a control mode that is performed without using the measured value of the air-fuel ratio sensor 50 (S230). ).
Specifically, the engine 60 is operated without using the air-fuel ratio sensor 50 based on data such as the rotational speed of the engine 60, the magnitude of the load, the opening degree of the throttle valve 25, and the like stored in advance in the ECU 10 or the like.
Control of the engine 60 that performs the process in step S230 is performed for a predetermined time stored in the ECU 10 in advance.
Then, the ECU executes the same processing as in steps S210 and S220 again to check the operation of the air-fuel ratio sensor 50 (S240 (similar to S210) and S250 (similar to S220)).
If it is determined in step S250 that the IP value is not greater than 0.7, the process proceeds to step S230. On the other hand, the IP value is determined to be greater than 0.7. In the case, the process proceeds to step S260.
When the process proceeds to step S260, since it is determined that the air-fuel ratio sensor 50 is normal, the ECU 10 enters a mode in which the air-fuel ratio control is performed using the measured value of the air-fuel ratio sensor 50.
That is, in the above description, even if some abnormality occurs in the air-fuel ratio sensor 50 in the above-described steps S210 and S220, if only the oil component is attached to the air-fuel ratio sensor 50, the steps S230 and S220 are performed. As shown in the processing of S240, by operating the engine for a predetermined time without using the air-fuel ratio sensor 50, the oil component attached to the air-fuel ratio sensor 50 is evaporated by the heater of the air-fuel ratio sensor 50 or exhaust heat, It can be incinerated.
As a result, the cause of the measurement abnormality of the air-fuel ratio sensor 50 due to the adhering oil is removed, and the control using the air-fuel ratio sensor 50 can be performed again.

Further, when the determination in step S145 described above corresponds to the case (1), the process proceeds to step S230.
When the case (1) is true, the air-fuel ratio sensor 50 is turned off when the measured value of the air-fuel ratio sensor 50 is smaller than a predetermined threshold value and the engine speed deviation is smaller than the predetermined threshold value. The engine 60 is operated for a predetermined period of time under control that is not used, and processing for confirming the operation of the air-fuel ratio sensor 50 is performed again.
Specifically, it is determined in step S125 that the vehicle is already rich based on the measured value of the air-fuel ratio sensor 50 (that is, it is determined that the measured value is smaller than a predetermined threshold value), and further rich avoidance air-fuel ratio control is performed. In other words, it can be said that the rotational speed deviation is within a threshold value (that is, smaller than a predetermined threshold value) and the engine 60 can be normally operated near the target rotational speed.
That is, in this case, it is understood that oil or the like is attached to the air-fuel ratio sensor 50 and temporarily shows richness, and the above steps S230, S240, S250, S260, etc. are sequentially performed to Similarly to the case, by evaporating or incinerating the oil component adhering to the air-fuel ratio sensor 50, it becomes possible to return the air-fuel ratio sensor 50 to a normal state and perform air-fuel ratio control again.
That is, in other words, even when oil is attached to the air-fuel ratio sensor 50 and the air-fuel ratio sensor 50 temporarily performs erroneous measurement, the engine 60 can be operated in a normal state. It becomes.

Further, when the determination in step S145 described above corresponds to the case of (2) above, the process proceeds to step S150.
In this case, the ECU 10 determines whether or not the fuel control valve 22 is fully closed (S150).
If it is determined in step S150 that the fuel control valve 22 is fully closed, the ECU 10 determines that an abnormality has occurred in the air-fuel ratio control system (S160), and operates the engine 60. Stop (S170).
When the operation of the engine 60 is stopped at the time of step S170, it may be notified to the outside by emitting a sound, light or the like as an alarm or the like.
When the process proceeds from step S150 to S160 to S170 as described above, the fuel control valve 22 is fully closed even though it is determined to be rich by the measurement of the air-fuel ratio sensor 50 in step S125 (S150). ) To obtain inconsistent measurement results.
Therefore, the ECU 10 determines that there is some abnormality in the entire air-fuel ratio control system in a state where such contradictory measurements are obtained, and stops the engine 60 in step S170.

Incidentally, the air-fuel ratio sensor 50 is provided in an exhaust passage such as an exhaust manifold of the engine 60, and measures the air-fuel ratio by measuring the oxygen concentration in the exhaust gas.
Here, the exhaust passage of the exhaust manifold or the like means an exhaust manifold or a collective portion of the exhaust manifold.
As described above, the air-fuel ratio sensor 50 needs to be activated by setting the temperature of the element of the air-fuel ratio sensor 50 to a certain temperature for accurate measurement. For this reason, the air-fuel ratio sensor 50 is provided with a heater. Yes.
However, even with such a configuration, the element part of the air-fuel ratio sensor 50 is cooled by the exhaust gas flowing through the exhaust passage such as the exhaust manifold, or the oil or condensed water contained in the exhaust gas is cooled. This causes problems such as being attached to the surface and being unable to measure accurately.
Therefore, as shown in FIG. 4, a protector 70 is provided in the air-fuel ratio sensor 50.
In the present embodiment, as shown in FIG. 4, the air-fuel ratio sensor 50 is indicated by a dotted line, and the protector 70 is indicated by a solid line. The alternate long and short dash line indicates an exhaust passage such as an exhaust manifold.
An element portion 51 is provided below the air-fuel ratio sensor 50. The element portion 51 is a portion provided in an exhaust passage such as an exhaust manifold, and is a portion that directly contacts exhaust gas.
Further, the element portion 51 is provided in a substantially cylindrical shape, and a plurality of vent holes 53 are provided in the middle part in the axial direction on the side surface, and a vent hole (not shown) is opened at the center portion of the tip. Exhaust gas is vented into the element portion 51 through the port 53 to measure the oxygen concentration.
In the air-fuel ratio sensor 50, the upper side of the element portion 51 protrudes to the outside of the exhaust passage such as an exhaust manifold, and is provided with a hexagon bolt portion 52 and the like.
Furthermore, a screw thread is formed on the upper side of the element portion 51 and is screwed with a screw thread provided on an inner peripheral surface of a cylindrical portion 72 of the protector 70 described later.
Therefore, when the air-fuel ratio sensor 50 and the protector 70 are fastened, the fastening can be easily performed by engaging a tool such as a spanner with the hexagon bolt 52.
By this fastening, the protector 70 is attached in the vicinity of the element portion 51 of the air-fuel ratio sensor 50.

Next, the protector 70 will be described with reference to FIG.
5A is a side view of the protector 70 viewed from the same direction as FIG.
FIG.5 (b) is the top view which looked at the protector 70 of Fig.5 (a) from the arrow b direction.
FIG. 5C is a side view of the protector 70 of FIG. 5A viewed from the direction of the arrow c, and shows a case where the air-fuel ratio sensor 50 is attached by a dotted line.
FIG.5 (d) is the bottom view seen from the arrow d direction of the protector 70 of Fig.5 (a).
The protector 70 has a flange portion 71 formed on the upper side, and a cylindrical portion 72 having a larger diameter than the element portion 51 of the air-fuel ratio sensor 50 is formed on the lower surface side of the flange portion 71.
Further, in the cylindrical portion 72, the upper end portion side on the flange portion 71 side is opened so that the element portion 51 can be inserted, and the lower end portion side is also opened, and a bridge 73 described later is integrally provided.
Therefore, when the protector 70 is attached to the air-fuel ratio sensor 50, the element portion 51 is configured to be accommodated in the cylindrical portion 72 of the protector 70 as shown in FIG.
In this case, the cylindrical portion 72 is formed such that the vent 53 provided in the element portion 51 is covered with the cylindrical portion 72 as shown in FIG.
That is, the lower end portion of the cylindrical portion 72 of the protector 70 is formed so as to be positioned below the vent 53 of the element portion of the air-fuel ratio sensor 50 so as to cover the vent 53.
Therefore, as shown in FIG. 1, the vent 53 of the element unit 51 does not directly contact the exhaust gas flowing in the exhaust passage such as the exhaust manifold.
Therefore, it is possible to avoid a situation in which the air-fuel ratio sensor 50 cannot be accurately measured because the inside of the element unit 51 is cooled by being exposed to exhaust gas ventilation, or oil or condensed water in the exhaust gas is attached. It becomes possible to do.
In addition, since the vent hole 53 is covered with the cylindrical portion 72, the heat retaining property of the element portion 51 is improved, and the measurement can be performed stably.

A bridge 73 is suspended from the lower end surface of the cylindrical portion 72 of the protector 70.
The bridge 73 has support portions 73a and 73a extending downward from both sides of the lower end surface of the cylindrical portion 72, and the support portions 73a and 73a are connected to each other by a connecting portion 73b on the lower end side of the support portions 73a and 73a. It is configured to be.
That is, the gap between the support portion 73a and the support portion 73a of the bridge 73 is configured to be larger than the outer shape of the element portion 51 of the air-fuel ratio sensor 50.
The bridge 73 formed in this way is formed so as to straddle the diameter direction of the cylindrical portion 72 on the distal end side of the cylindrical portion 72 of the protector 70 so that the element portion 51 is located inside thereof.
Furthermore, when the protector 70 is attached to the air-fuel ratio sensor 50, the lengths of the support portions 73a and 73a are determined so that a gap is formed between the bridge 73 and the tip portion of the element portion 51.
Specifically, as shown in FIG. 5C, the support portions 73a and 73a are set such that a gap between the tip portion of the element portion 51 and the upper surface side of the connecting portion 73b of the bridge 73 is n [mm]. The length of is decided.
The range of n [mm] of the gap is a gap through which exhaust gas can enter from the vent opening opened at the tip of the element portion 51. If the gap is too large, the effect of shielding oil and the like by the bridge 73 is lost. It is desirable to be within about 5 mm.
In this way, by configuring the bridge 73, it is possible to prevent the oil component or the condensed water in the exhaust gas from adhering to the tip portion of the element unit 51, and to prevent the air-fuel ratio sensor 50 from deteriorating or malfunctioning. Is possible.

For example, as shown in FIG. 4, the protector 70 may be attached to the exhaust passage such as the exhaust manifold so that the bridge 73 is perpendicular to the direction of the exhaust gas flowing in the exhaust passage such as the exhaust manifold. desirable.
This is because when the protector 70 is attached to an exhaust passage such as an exhaust manifold as described above, the power supplied to the heater of the air-fuel ratio sensor 50 can be kept low.
Specifically, as shown in FIG. 6, it is known that the duty ratio of the heater of the air-fuel ratio sensor 50 becomes small.
The duty ratio is a ratio of energization time over a certain period of time when power is generally supplied while repeating energization and interruption to control to a desired temperature.
Therefore, for example, when the duty ratio is 100 [%], it means that the energization is continuously performed and is not cut off, and when the duty ratio is 50 [%], the energization time and the cut-off are cut off. It can be said that time is the same ratio.
Therefore, in general, it can be said that the greater the duty ratio [%], the greater the amount of power used.
In FIG. 6, the vertical axis represents the duty ratio of the heater of the air-fuel ratio sensor 50, and the horizontal axis represents the relationship between the bridge width and the mounting direction.
The line 110 has an energization voltage of 14.7 [V], the line 120 has an energization time of 14.0 [V], the line 130 has an energization time of 13.1 [V], and the line 140 has an energization time of 12.6 [V]. The points plotted for the duty ratio in the case of [V] are connected.
In FIG. 6, the lines when the bridge 73 is parallel to the direction of the exhaust gas flowing in the exhaust passage such as the exhaust manifold are the lines 110a to 140a, and the bridge 73 is the exhaust passage such as the exhaust manifold. Lines at a right angle to the direction of the exhaust gas flowing inside are shown as lines 110b to 140b.
As shown in FIG. 6, it can be seen that the line 110b to line 140b may have a smaller overall duty ratio than the lines 110a to 140a.
In other words, if the bridge 73 is attached so as to be perpendicular to the direction of the exhaust gas, the duty ratio can be reduced, the heat retention of the air-fuel ratio sensor 50 is improved, and the amount of power used for the heater is suppressed. Thus, the air-fuel ratio sensor 50 can be stably activated and accurately measured.
In addition, the lower the applied voltage applied to the heater, the smaller the duty ratio can be suppressed, and the wider the bridge width, the smaller the duty ratio can be suppressed.
As described above, generally, the protector 70 is attached to an exhaust passage such as an exhaust manifold so that the bridge 73 is perpendicular to the direction of the exhaust gas, and the applied voltage of the heater is kept low, and the width of the bridge 73 is increased. Thus, the duty ratio can be suppressed to a small value, and the air-fuel ratio sensor 50 can be stably activated and accurately measured.

1 is a schematic configuration diagram of an air-fuel ratio control system according to an embodiment of the present invention. The flowchart which showed an example of the series of processes which an air fuel ratio control system performs. The flowchart which showed an example of the series of processes which an air fuel ratio control system performs. The external view at the time of attaching an air fuel ratio sensor (dotted line part) to a protector (solid line part). The external view of a protector. The graph which showed the duty ratio in the case of heating the heater provided in an air fuel ratio sensor.

Explanation of symbols

10 ECU
22 Fuel control valve 25 Throttle valve 25
44 Rotational Speed Sensor 50 Air-Fuel Ratio Sensor 51 Element Part 53 Ventilation Port 60 Engine 70 Protector 71 Gutter Part 72 Cylindrical Part 73 Bridge 73a Support Part 73b Connection Part

Claims (9)

In the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
When air-fuel ratio control is started within a predetermined time after the air-fuel ratio sensor becomes measurable,
An air-fuel ratio control system characterized by slowing the operating speed of a fuel control valve. In the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
When air-fuel ratio control is started after a predetermined time has elapsed since the air-fuel ratio sensor can be measured,
An air-fuel ratio control system characterized by slowing a closing operation speed in a closing operation of a fuel control valve. In the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
When air-fuel ratio control is started after a predetermined time has elapsed since the air-fuel ratio sensor can be measured,
An air-fuel ratio control system characterized by increasing an opening operation speed in an opening operation of a fuel control valve. In the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
When the measured value of the air-fuel ratio sensor is smaller than a predetermined threshold value and the engine is stopped,
An air-fuel ratio control system for confirming the operation of an air-fuel ratio sensor. When it is determined as abnormal in the operation check of the air-fuel ratio sensor,
The air-fuel ratio control system according to claim 4, wherein the engine is operated for a predetermined time by control without using the air-fuel ratio sensor, and the operation of the air-fuel ratio sensor is confirmed again. In the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
When the measured value of the air-fuel ratio sensor is smaller than a predetermined threshold and the engine speed deviation is smaller than a predetermined threshold,
An air-fuel ratio control system comprising: operating an engine for a predetermined time by control without using an air-fuel ratio sensor; and confirming the operation of the air-fuel ratio sensor again. In the air-fuel ratio control system for controlling the air-fuel ratio of the air-fuel mixture based on the measured value of the air-fuel ratio sensor,
A substantially cylindrical protector for protecting the element portion of the air-fuel ratio sensor is provided,
Form a bridge across the diameter direction at the tip of the protector,
The width of the bridge is larger than the outer shape of the element portion of the air-fuel ratio sensor,
An air-fuel ratio control system, wherein a gap is formed between the bridge and the element portion of the air-fuel ratio sensor.   The air-fuel ratio control system according to claim 7, wherein the bridge of the protector is attached to an exhaust passage such as an exhaust manifold so as to be perpendicular to an exhaust flow.   9. The air-fuel ratio control system according to claim 7, wherein a lower end portion of a cylindrical side surface of the protector is formed so as to cover a vent hole of an element portion of the air-fuel ratio sensor.

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