JP2002285904A - Diagnostic apparatus for intake oxygen concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To readily and correctly determine failure of an intake oxygen concentration sensor. SOLUTION: A fuel injection amount of an engine at a time of evaporated fuel purging is corrected, based on the outputs from the intake oxygen concentration sensor 31 arranged to an intake passage of the internal combustion engine. In an electronic control unit(ECU) for controlling the engine, sensor outputs 31 under different two intake pressures are measured, a sensor output characteristics value is calculated from a changing amount of the intake pressures and a changing amount of the sensor outputs, and the failure of the sensor 31 is determined to exist, when the output characteristics value is not less than a predetermined upper limit value or not more than a prescribed lower limit value. The upper limit is set based on the tolerance in the variations of the sensor outputs of respective products, and the lower limit is set in consideration of influence of lowering of actual intake oxygen concentration caused by the evaporated fuel purging or EGR. Therefore, the failure of the sensor is checked readily and correctly, so that failures of the sensor can be detected early.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diagnostic device for determining the presence or absence of a failure in an intake oxygen concentration sensor.

[0002]

2. Description of the Related Art An internal combustion engine is provided with an air-fuel ratio sensor for detecting an exhaust air-fuel ratio in an exhaust passage of an engine, and the amount of fuel supplied to the engine is feedback-controlled so that the detected exhaust air-fuel ratio becomes a predetermined target air-fuel ratio. BACKGROUND ART An air-fuel ratio control device for an engine is known. In such an air-fuel ratio control device, for example, parameters related to the engine intake air amount are measured, and the engine is controlled so that the exhaust air-fuel ratio matches the target air-fuel ratio based on a relationship stored in advance using these parameters. The basic fuel supply amount (basic fuel injection amount) is calculated, and the amount of fuel obtained by correcting the basic fuel supply amount so that the exhaust air-fuel ratio detected by the exhaust air-fuel ratio sensor matches the target air-fuel ratio is actually calculated. Supply to the organization.

As described above, a sensor (for example, an air flow meter) that detects a parameter related to an engine intake air amount by feedback-correcting a basic fuel injection amount based on an actual exhaust air-fuel ratio detected by an air-fuel ratio sensor. Accurate air-fuel ratio control because errors in the fuel injection amount due to variations in the actual fuel injection amount of the fuel injection valve for each product and aging are corrected. Becomes possible. However, in an engine provided with an evaporative fuel purging device for purging evaporative fuel from a fuel tank in an engine intake passage, even when the feedback control based on the exhaust air-fuel ratio sensor is performed as described above, the start of the evaporative fuel purge is not performed. At the end, there may be a case where the engine air-fuel ratio temporarily deviates from the target air-fuel ratio.

That is, when the evaporated fuel (hydrocarbon) is introduced into the intake passage by the purge, the fuel vapor flows into the engine together with the intake air in addition to the fuel supplied by the fuel injection. For this reason, even if the fuel injection amount to the engine is controlled based on the exhaust air-fuel ratio, the fuel supply amount to the engine temporarily increases, and the engine air-fuel ratio may deviate from the target air-fuel ratio. Even if such a shift occurs,
If the feedback control of the engine fuel injection amount based on the exhaust air-fuel ratio is performed, the fuel supply amount to the engine by the purge is corrected and the engine air-fuel ratio becomes equal to the target air-fuel ratio. Since the gain is set to a relatively small value in order to prevent hunting of the control, when a large amount of purge is performed, the engine air-fuel ratio is increased only by the air-fuel ratio feedback control based on the output of the exhaust air-fuel ratio sensor. It may take some time to converge on the target air-fuel ratio.

In order to solve this problem, an intake oxygen concentration sensor for detecting oxygen concentration in intake air is disposed in an engine intake passage, and the amount of fuel vapor introduced into the intake passage is calculated based on the detected intake oxygen concentration. Controls have been devised. When evaporative fuel (hydrocarbon) is introduced into the intake passage, the evaporative fuel in the intake air is burned by an oxidation catalyst provided in an oxygen concentration detecting unit of the sensor, and the oxygen concentration near the detecting unit burns the amount of evaporated fuel ( That is, it decreases according to the fuel vapor concentration). Therefore, the evaporative fuel (vapor) concentration in the intake air is calculated based on the output of the intake oxygen concentration sensor, and the amount of vapor supplied to the engine is calculated based on the engine intake air amount and the vapor concentration. By reducing the fuel injection amount to the engine by a corresponding amount, it becomes possible to accurately control the air-fuel ratio even during the execution of the purge.

However, when the engine fuel injection is corrected using the intake oxygen concentration sensor, the pressure dependency of the output of the intake oxygen concentration sensor becomes a problem. As is generally known, an inspired oxygen concentration sensor arranges a solid electrolyte such as zirconia between two platinum electrodes functioning as a cathode and an anode, and forms oxygen molecules in the inspired air on a cathode (intake side electrode) surface. It has a structure provided with a diffusion-controlling layer such as a ceramic coating layer that restricts reaching the cathode. An intake oxygen concentration sensor is arranged so that the cathode is in contact with the engine intake air, the anode is arranged so as to be in contact with the atmosphere, and a voltage is applied between both electrodes at a certain temperature or higher. Oxygen molecules therein are ionized, and the ionized oxygen molecules move inside the solid electrolyte toward the anode (atmosphere-side electrode) to generate an oxygen pumping action to become oxygen molecules again at the anode. Due to this oxygen pump action, a current proportional to the amount of oxygen molecules moved per unit time flows between the two electrodes. However, since the diffusion controlling layer limits the arrival of oxygen molecules to the cathode, the output current saturates at a certain constant value, and the current does not increase even if the voltage is increased. The value of the saturation current is substantially proportional to the oxygen partial pressure (concentration) in the intake air. Therefore, by appropriately setting the applied voltage, an output current substantially proportional to the oxygen concentration can be obtained. By converting this output current into a voltage signal, a voltage signal proportional to the oxygen concentration (partial pressure) in the intake air is obtained by the intake oxygen concentration sensor. In addition, when hydrocarbons such as fuel vapor are contained in the intake air, the hydrocarbons burn on the platinum electrode and the oxygen concentration in the vicinity of the electrode decreases, so the oxygen concentration sensor detects the hydrocarbons contained in the intake air. A voltage signal proportional to the oxygen concentration after burning the combustible material is output.

When the pressure is constant, the oxygen concentration in the intake air becomes equal to the oxygen partial pressure in the intake air (more precisely, the ratio between the oxygen partial pressure and the intake air pressure). However, even if the oxygen concentration is constant, if the intake pressure changes, the oxygen partial pressure in the intake changes in proportion to the intake pressure, so that the oxygen partial pressure differs. On the other hand, the intake oxygen concentration sensor detects the oxygen partial pressure in the intake air. Therefore, even if the oxygen concentration in the intake air is kept constant, if the oxygen partial pressure changes due to the change in the intake pressure, the sensor output changes. Would. That is, the oxygen concentration signal output from the intake oxygen concentration sensor has a so-called pressure dependency in which the oxygen concentration signal changes linearly in proportion to the intake pressure even when the oxygen concentration is constant. The engine intake pressure changes according to the engine load state such as the engine load and the number of revolutions. For this reason, as described above, when correcting the fuel injection amount to the engine based on the oxygen concentration in the intake air detected by the intake oxygen concentration sensor, it is necessary to correct the sensor output according to the intake pressure.

In general, the correction of the sensor output is performed based on a reference pressure change characteristic of the sensor output previously detected for each type (model) of the sensor by detecting the engine intake pressure. However, even if the oxygen concentration is constant, the output of the intake oxygen concentration sensor changes depending on the thickness of the diffusion-controlling layer and the zirconia solid electrolyte. In addition, an explosion-proof cover is provided on the detection unit of the intake oxygen concentration sensor to prevent combustion of combustibles such as hydrocarbons on the platinum electrode from igniting the combustibles in the intake air. Are provided with pores for introducing the intake air to the sensor detecting section. However, if the size of the pores varies within the manufacturing tolerance, the output of the oxygen concentration sensor changes accordingly. For this reason, even with the same type of sensor, the sensor output and the above-described pressure-dependent characteristics may vary from sensor to sensor due to manufacturing variations. Therefore, when correcting the output of the intake oxygen concentration sensor according to the intake pressure, if the pressure-dependent characteristics of the sensor output vary from product to product, the sensor output may be corrected using the above-described reference pressure change characteristics. An accurate intake oxygen concentration cannot be detected, and a problem arises in that the fuel supply amount to the engine cannot be accurately controlled.

Japanese Patent Application Laid-Open No. Hei 10-176577 discloses a control device for an internal combustion engine capable of correcting the above-mentioned variation in the pressure dependency of the output of the intake oxygen concentration sensor for each product and obtaining an accurate intake oxygen concentration. are doing. In the apparatus disclosed in the above publication, a condition in which the output of the intake oxygen concentration sensor is not affected by a change other than the pressure change, that is, a condition in which the oxygen concentration in the engine intake does not change (for example, a part of the engine exhaust is recirculated to the engine intake passage) Under conditions where exhaust gas recirculation (EGR) and evaporative fuel purging are not performed), the intake pipe pressure and the intake oxygen concentration sensor output are measured, and the rate of change of the sensor output with respect to the intake pipe pressure change is calculated. By correcting the sensor output at each pressure based on the rate of change, variation in the sensor output for each product is corrected, and an accurate intake oxygen concentration is calculated.

[0010]

However, in the apparatus disclosed in Japanese Patent Application Laid-Open No. H10-176577, although the pressure-dependent characteristics of the output of the intake oxygen concentration sensor can be accurately corrected for each product, the sensor fails. A problem arises because it is not possible to determine whether or not this has been done.

[0011] For example, the intake oxygen concentration sensor tends to deteriorate with use for a long time, and the output tends to increase for the same oxygen concentration. Also, in an engine equipped with a PCV device for performing crankcase ventilation, the above-described intake oxygen concentration sensor is used for oil particles and hydrocarbons contained in the crankcase discharge gas circulated from the crankcase to the intake passage. In some cases, clogging of the pores for introducing air into the explosion-proof cover may occur, and the output of the sensor may be significantly changed.

In the apparatus disclosed in the above publication, even if such a failure occurs, the presence or absence of a sensor failure cannot be determined. Therefore, the fuel injection amount is corrected based on the output of the failed sensor, and the exhaust air amount is corrected. There is a problem that a deviation of the fuel ratio from the target value occurs, which causes deterioration of exhaust emission and deterioration of engine operation performance. Further, in the device disclosed in the publication, even when the sensor fails, the sensor output is corrected in the same manner as in the case of a normal sensor, so that the deviation of the sensor output from the true value is further increased, and the emission is deteriorated. And the deterioration of the driving performance may be further increased.

In view of the above problems, the present invention can easily and accurately determine the presence or absence of a sensor failure when using an intake oxygen concentration sensor, and prevent control based on the output of the failed sensor from being continued. It is an object of the present invention to provide a diagnostic device for an intake oxygen concentration sensor.

[0014]

According to the first aspect of the present invention, the presence or absence of a failure of an intake oxygen concentration sensor arranged in an intake passage of an internal combustion engine and generating an output corresponding to the oxygen concentration in the intake air of the engine is determined. A failure determination device for determining, wherein an intake pressure detecting means for detecting an engine intake pressure, and when the engine intake pressure changes, an output change amount of the intake oxygen concentration sensor with respect to a change amount of the engine intake pressure is predetermined. A determination device for determining whether or not the oxygen concentration sensor has failed based on whether or not the relationship is satisfied is provided.

That is, according to the first aspect of the present invention, the presence or absence of a sensor failure is determined based on whether or not the change in the output of the intake oxygen concentration sensor with respect to the change in the engine intake pressure satisfies a predetermined relationship. For example, the output of the oxygen concentration sensor changes linearly with respect to the intake pressure, and the output also becomes 0 when the intake pressure is 0 (that is, when the sensor output is plotted on the vertical axis and the intake pressure is plotted on the horizontal axis, it is normal). The output characteristic of a simple oxygen concentration sensor is a straight line passing through the origin. This straight line represents the pressure dependent characteristics of the sensor. Even when an abnormality occurs in the sensor, the sensor output changes with respect to the intake pressure, but the sensor output characteristic deviates from a straight line, or the straight line does not pass through the origin. Therefore, when the deviation of the sensor output characteristic from the straight line or the deviation between the output characteristic and the origin is equal to or larger than a predetermined value, it can be determined that the sensor has failed. As described above, the presence / absence of a sensor failure can be determined easily and accurately by determining the presence / absence of a sensor failure based on the change amount of the sensor output with respect to the intake pressure change amount. Control is prevented from continuing.

According to the second aspect of the present invention, the determining means determines whether the intake pressure detected by the intake pressure detecting means is the first pressure and a second pressure different from the first pressure. The output of the oxygen concentration sensor at the time of
And a change characteristic of the sensor output with respect to the pressure based on the ratio of the difference between the first sensor output and the second sensor output with respect to the difference between the first pressure and the second pressure. The intake air oxygen concentration sensor according to claim 1, further comprising calculating a characteristic value to represent, and determining that the intake oxygen concentration sensor has failed when the calculated characteristic value is equal to or more than a predetermined upper limit or equal to or less than a predetermined lower limit. A diagnostic device for an intake oxygen concentration sensor is provided.

That is, according to the second aspect of the present invention, the first sensor output and the second sensor output with respect to the difference between the first pressure and the second pressure are based on the sensor output values at two different pressures. A characteristic value representing the pressure-dependent characteristic of the sensor output is calculated based on the ratio of the difference between the two. If the characteristic value is equal to or more than a predetermined upper limit value or equal to or less than a lower limit value, it is determined that the sensor has failed. This makes it possible to easily and accurately determine the presence or absence of a sensor failure by measuring the sensor output twice when the intake pressure changes during engine operation.

Note that the characteristic value of the sensor output is, for example, the origin (the pressure is 0,
The sensor output is a value representing a deviation from a straight line passing through 0). For example, the dimensionless change amount of the intake pressure (the difference between the first pressure and the second pressure is expressed by the first or second sensor output). A dimensionless value obtained by dividing the difference between the first sensor output and the second sensor output by the first or second sensor output with respect to the dimensionless change amount of the sensor output with respect to the value obtained by dividing by the first or second sensor output. ) Ratio is used.

According to the third aspect of the present invention, the upper limit value is set based on an output variation tolerance of each product of the intake oxygen concentration sensor, and the lower limit value is set when exhaust gas recirculation to the engine intake is performed. The diagnostic device for an intake oxygen concentration sensor according to claim 2, wherein the diagnostic device is set based on the intake oxygen concentration change amount of the intake air and / or the intake oxygen concentration change amount when the introduction of the hydrocarbon component into the engine intake is performed. You.

That is, according to the third aspect of the present invention, the upper limit value for determining the presence or absence of a sensor failure is set based on the output variation tolerance of the oxygen concentration sensor. The output variation tolerance of the oxygen concentration sensor is in a standard state (for example, when the intake air pressure is 1 atm (7
60 mmHg) in the case of the atmosphere) and the ratio to the reference sensor output. In the present invention, the output characteristic value,
That is, if the deviation of the pressure-dependent characteristic of the sensor from the straight line exceeds this tolerance, it is determined that the sensor has failed. As described above, the pressure-dependent characteristic line of the sensor output serving as a reference is a case where the intake air is in the standard state atmosphere, so that the oxygen concentration does not become larger than the standard state in the actual operation. Therefore, when the output characteristic value is equal to or more than the upper limit corresponding to the variation tolerance of each product, it can be determined that the sensor has failed.

On the other hand, the lower limit in the failure determination is for determining a failure in which the sensor output becomes lower than the actual oxygen concentration in the intake air. In this case, during engine operation, purge or EGR
Is executed or the PCV valve is opened and the crankcase discharge gas is recirculated to the intake air, the oxygen concentration in the intake actually becomes lower than the oxygen concentration in the atmosphere. For this reason, in the present invention, the lower limit at the time of failure determination is set in consideration of the actual decrease width of the oxygen concentration when purging or EGR is performed, and failure diagnosis is performed during execution of purging or EGR. In this case, a normal sensor is prevented from being determined to be abnormal. This makes it possible to determine the presence / absence of a sensor failure even at the time of purging or EGR, thereby increasing the chances of executing the presence / absence determination of a sensor failure.

According to the fourth aspect of the invention, when neither the exhaust gas recirculation to the engine intake air nor the introduction of the hydrocarbon component into the engine intake air is performed, the lower limit value is set to the intake oxygen concentration. 4. The diagnostic device for an intake oxygen concentration sensor according to claim 3, wherein the diagnostic device is set based on an output variation tolerance of each sensor product.

That is, according to the fourth aspect of the present invention, when both the recirculation of the exhaust gas to the engine intake and the introduction of the hydrocarbon component are not performed (for example, when the purge or the EGR is not performed). The lower limit value at the time of failure determination is also set based on the variation tolerance of the sensor output. As a result, more accurate sensor failure determination can be performed than in the case of the determination of claim 3.

According to the fifth aspect of the present invention, when the exhaust gas is recirculated during the operation of the engine or when the hydrocarbon component is introduced into the engine intake, the characteristic value becomes equal to or less than the lower limit value, and the intake oxygen concentration sensor is operated. If it is determined that it has failed,
Again, the characteristic value is calculated when both the exhaust gas recirculation to the engine intake and the introduction of the hydrocarbon component into the engine intake are not performed, and the failure of the intake oxygen concentration sensor based on the characteristic value is calculated. A diagnostic device for an intake oxygen concentration sensor according to claim 4, wherein the determination is performed.

That is, in the invention of claim 5, claim 4
In the case where it is determined that the sensor has failed because the slope of the pressure-dependent characteristic line of the sensor output calculated at the time of introducing EGR or hydrocarbons into the intake air has fallen below the lower limit value, If the introduction has not been performed, the presence / absence of a sensor failure is determined again. As previously mentioned,
When EGR and hydrocarbons are introduced into the intake air, the oxygen concentration in the intake air actually decreases, so that the accuracy of the determination becomes slightly lower than the sensor failure determination when these are not performed, and the normal sensor fails. There is a slight possibility of being judged. According to the present invention, when the sensor is determined to be faulty based on the lower limit value when the EGR or hydrocarbon is introduced into the intake air, the normal sensor is faulty by determining again whether or not there is a fault in a state of high determination accuracy. Erroneous determination is completely prevented.

[0026]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to an internal combustion engine for a vehicle. In FIG. 1, reference numeral 1 denotes an automobile internal combustion engine. In the present embodiment, the engine 1 is a four-cylinder gasoline engine having four cylinders # 1 to # 4, and each cylinder is provided with in-cylinder fuel injection valves 111 to 114 for directly injecting fuel into the cylinder. ing.

Further, in this embodiment, the cylinders # 1 to # 4 are grouped into two cylinder groups including two cylinders whose ignition timings are not continuous with each other. (For example, in the embodiment of FIG. 1, the cylinder ignition order is 1-3-4-2,
The cylinders # 1 and # 4 and the cylinders # 2 and # 3 each constitute a cylinder group. The exhaust port of each cylinder is connected to an exhaust manifold for each cylinder group, and is connected to an exhaust passage for each cylinder group. In FIG. 1, 21a is # 1, # 4
The exhaust manifold 21b connects the exhaust ports of the cylinder group consisting of cylinders to the individual exhaust passages 2a, and the exhaust manifold 21b connects the exhaust ports of the cylinder groups consisting of # 2 and # 3 cylinders to the individual exhaust passage 2b. In the present embodiment, start catalysts (hereinafter, referred to as "SC") 5a and 5b made of a known three-way catalyst are arranged on the individual exhaust passages 2a and 2b, respectively. The individual exhaust passages 2a and 2b are S
It joins the common exhaust passage 2 on the downstream side of C.

Reference numerals 29a and 29b in FIG. 1 denote air-fuel ratio sensors disposed upstream of the start catalysts 5a and 5b in the individual exhaust passages 2a and 2b. Air-fuel ratio sensor 2
Reference numerals 9a and 29b denote sensors having the same configuration as an intake oxygen concentration sensor described later, and output a voltage signal corresponding to the exhaust air-fuel ratio in a wide air-fuel ratio range. Air-fuel ratio sensor 29
The outputs of a and 29b are used for controlling the air-fuel ratio of the engine 1.
Reference numeral 10b in FIG. 1 denotes an intake manifold connecting the intake ports of each cylinder of the engine to the intake passage 10, and 10a denotes a surge tank provided in the intake passage 10. Further, in this embodiment, a throttle valve 15 is provided on the intake passage 10. The throttle valve 15 of the present embodiment is a so-called electronically-controlled throttle valve, and is driven by an appropriate type of actuator 15a such as a stepper motor or the like, and has an opening in accordance with a control signal from an ECU 30 described later.

A known fuel vapor purge device 40 is connected to the intake passage 10 downstream of the throttle valve 15 via a purge control valve 41. The purge device 40 includes a canister containing an adsorbent such as activated carbon, for example.
The fuel vapor in the fuel tank (not shown) of the engine 1 is adsorbed by the adsorbent in the canister. This prevents the evaporation of the fuel vapor from the fuel tank to the atmosphere. The purge control valve 41 includes an actuator of an appropriate type such as a stepper motor, and takes an opening degree according to a control signal of the ECU 30. When the purge control valve 41 is opened during operation of the engine, the fuel vapor adsorbed in the canister of the purge device 40 flows into the intake passage 10 from the purge control valve 41,
The mixture with the engine intake air that has passed through the throttle valve 15 becomes a uniform mixture and is taken into each cylinder of the engine 1.

The surge tank 10a of the intake passage 10
Is connected to an EGR passage 53 via an EGR control valve 51. The EGR passage 53 connects the exhaust manifolds 21a and 21b of the engine 1 and the surge tank 10a, and recirculates a part of the engine exhaust to the engine intake passage, thereby lowering the combustion temperature in the combustion chamber of the engine 1 to reduce the combustion temperature. This is to reduce the amount of generated NO _X. The EGR control valve 51 includes an actuator of an appropriate type such as a stepper motor, takes an opening in accordance with a control signal of the ECU 30, and exhaust gas (EG) which is recirculated to the intake passage during operation of the engine.
(R gas) The flow rate is adjusted according to the engine operating condition.

Further, in this embodiment, an oxygen concentration sensor 31 for detecting the oxygen concentration in the intake air is disposed in the surge tank 10a of the intake passage 10. Oxygen concentration sensor 3
1 outputs a voltage signal proportional to the oxygen concentration (partial pressure) in the exhaust gas by the action of the oxygen pump, as described above. In FIG. 1, reference numeral 30 denotes an electronic control unit (EC) of the engine 1.
U). In this embodiment, the ECU 30 includes a RAM, an R
The microcomputer is a microcomputer having a known configuration including an OM and a CPU, and performs a determination operation for determining whether or not a failure has occurred in an intake oxygen concentration sensor 31 described later. The ECU 30 performs basic control such as ignition timing control and air-fuel ratio control of the engine 1,
The opening and closing of the purge control valve 41 and the EGR control valve 51 are controlled to perform purge of the evaporated fuel and EGR.

Further, the ECU 30 calculates the amount of fuel vapor during intake based on the output of the intake oxygen concentration sensor 31 at the time of purging, and based on the amount of fuel vapor, the fuel injection amount of the fuel injection valves 111 to 114 of each cylinder. Is performed to correct the fuel vapor. To perform each of the above controls, the ECU 3
A signal representing the exhaust air-fuel ratio from the air-fuel ratio sensors 29a and 29b and a signal representing the oxygen concentration in the intake air from the intake oxygen concentration sensor 31 are provided at an input port of 0, and an intake pressure sensor provided in the engine intake manifold. Signals corresponding to the intake pipe pressure of the engine are input from 33 respectively.

The output port of the ECU 30 is connected to the fuel injection valves 111 to 114 of each cylinder via a fuel injection circuit (not shown) for controlling the amount and timing of fuel injection to each cylinder. The throttle valve 15 is connected to an actuator 15b of the throttle valve 15 via a drive circuit (not shown) to control the opening of the throttle valve 15. Also, ECU
Numeral 30 is connected to respective actuators of the purge control valve 41 and the EGR control valve 51 via a drive circuit (not shown) to control the opening degree of the purge control valve 41 and the EGR control valve 51 to perform the purge of the evaporated fuel and the EGR. Do.

In this embodiment, the intake oxygen concentration sensor is used for controlling the engine fuel injection amount and the EGR amount at the time of evaporative fuel purging. That is, in the present embodiment, the ECU 30 operates the engine 1 in a wide air-fuel ratio range from a rich air-fuel ratio to a lean air-fuel ratio. For example, when the engine 1 is operated at a rich air-fuel ratio or a stoichiometric air-fuel ratio, The engine fuel injection amount is calculated based on the engine intake air amount calculated from the intake pressure PM and the rotational speed NE and the target air-fuel ratio of the engine, and furthermore, feedback control based on the outputs of the exhaust air-fuel ratio sensors 29a and 29b. Is corrected by

The intake air amount GA of the engine is determined by the intake pressure of the engine and the engine speed, and the intake air amount GA can be calculated by measuring the intake pressure PM and the engine speed NE. Further, when the intake air amount GA is determined, the fuel injection amount (basic fuel injection amount) GFB required to make the operating air-fuel ratio of the engine coincide with the target air-fuel ratio is GFB = GA /
It can be calculated as RT. In the present embodiment, when the engine is operated at an air-fuel ratio other than the stoichiometric air-fuel ratio, the value of the basic fuel injection amount GFB is the target air-fuel ratio RT and the intake pressure P
ECU in the form of a numerical map using M and engine speed NE
30 are stored in the ROM.

The actual engine fuel injection amount GF is calculated as follows using the basic fuel injection amount GFB. GF = GFB × EFKG × FAF (1) Here, the FAF is used to make the engine air-fuel ratio calculated based on the exhaust air-fuel ratio detected by the exhaust air-fuel ratio sensors 29a and 29b exactly coincide with the target air-fuel ratio. And is referred to as an air-fuel ratio feedback correction coefficient. The air-fuel ratio feedback correction coefficient is calculated by, for example, proportional, integral, and differential (PID) control based on the deviation between the target air-fuel ratio and the exhaust air-fuel ratio detected by the exhaust air-fuel ratio sensors 29a and 29b.
EFKG is a learning correction coefficient for correcting a sensor detection error of the air-fuel ratio control system and a fuel injection error of the fuel injection valves 111 to 114. In the present embodiment, the air-fuel ratio feedback correction coefficient FAF and the learning correction coefficient EFK
As a method for calculating G, any known method can be used, and a detailed description of the calculation method will be omitted.

Next, the correction of the fuel injection amount during the execution of the evaporated fuel purge will be described. When the purge of the evaporated fuel is performed, the purged fuel is supplied to the engine in the form of a fuel vapor in addition to the fuel supplied to the engine by the fuel injection. Therefore, if the fuel amount GF calculated by the above equation (1) is supplied to the engine, the fuel becomes excessive by the amount of the fuel vapor, and the target air-fuel ratio cannot be maintained. Thus, in the present embodiment, the air-fuel ratio control is affected by the evaporative fuel purge by reducing the fuel injection amount GF by the fuel vapor based on the output of the intake oxygen concentration sensor 31 disposed in the intake passage. Has been prevented.

In this embodiment, the intake oxygen concentration sensor 31
The above-described fuel vapor amount correction is performed based on the sensor output ratio α calculated based on the output of the above. The sensor output ratio α is the output of the intake oxygen concentration sensor 31 when the purge is not executed, that is, the output of the intake oxygen concentration R0 when the purge is not executed and the output of the oxygen concentration sensor 31 during the purge execution (the intake air during the purge execution). Oxygen concentration) RP, that is, α =
Given as RP / R0.

When fuel vapor is present in the intake air, the oxygen in the intake reacts with the fuel vapor on the sensor 31 and is consumed.
Therefore, on the sensor 31, the oxygen concentration is reduced by the amount consumed for the reaction with the fuel vapor, and the sensor output becomes RP. That is, of the oxygen in the intake air, an amount of oxygen corresponding to R0 × (1−α) is consumed by the reaction with the fuel vapor. Therefore, when the target air-fuel ratio of the engine is the stoichiometric air-fuel ratio (excess air ratio λ = 1), the ratio of the oxygen available for combustion supplied by the fuel injection to the oxygen in the intake air is R0 × α. Becomes For this reason, in order to maintain the operating air-fuel ratio of the engine at the stoichiometric air-fuel ratio, the fuel injection amount is reduced by the amount that the ratio of oxygen available for combustion is reduced with respect to the fuel injection amount when purging is not performed. If it is reduced, it is possible to maintain the same air-fuel ratio as when no purging is performed. Therefore, in this case, if the fuel injection amount is reduced by α times (α ≦ 1), it is possible to maintain the same air-fuel ratio as when there is no vapor.

That is, in the present embodiment, the ECU 30 calculates the actual fuel injection amount GFTA from the fuel injection valve when the target air-fuel ratio is the stoichiometric air-fuel ratio by the GF calculated by the equation (1).
Is multiplied by the sensor output ratio α. That is, GFTA = GF × α = GFB × α × EFKG × FAF (2) As a result, the fuel injection amount is controlled to a value that can accurately obtain the target air-fuel ratio even during execution of the evaporative fuel purge. Become. In the above description, the case where the target air-fuel ratio is the stoichiometric air-fuel ratio has been described. However, even when the target air-fuel ratio is the lean air-fuel ratio or the rich air-fuel ratio, the fuel vapor amount during intake based on the output of the intake oxygen concentration sensor 31 is determined. By performing the calculation and performing the same fuel injection amount correction, the target air-fuel ratio can be accurately maintained even when the purge is performed.

When performing EGR, the ECU 30 performs feedback control of the opening of the EGR valve 51 so that the oxygen concentration detected by the intake oxygen concentration sensor 31 becomes a predetermined value corresponding to the operating state. As a result, the flow rate of the recirculated exhaust gas (EGR) recirculated to the intake passage 10 through the EGR valve 51 is always controlled to an optimal amount according to the engine operating state. As described above, the intake oxygen concentration sensor 31 plays an important role in engine air-fuel ratio control.
If a failure occurs in the engine, there is a possibility that engine performance and emission may be deteriorated due to disturbance of the engine air-fuel ratio. Therefore, in the present embodiment, the presence or absence of a failure in the intake oxygen concentration sensor 31 is determined by the method described below, and the sensor failure is detected early.

Hereinafter, the principle of the failure determination of the intake oxygen concentration sensor according to the present invention will be described. FIG. 2 is a diagram showing changes in pressure and sensor output when standard air (oxygen concentration 21%) is measured by a general oxygen concentration sensor. As described above, since the oxygen concentration sensor output RP changes in proportion to the partial pressure of oxygen in the air, even when the oxygen concentration is constant, the oxygen concentration sensor output also changes in proportion to the pressure. That is, as shown in FIG. 2, the vertical axis represents the sensor output RP,
When the gas (air) pressure PM to be detected is plotted on the horizontal axis, the relationship between sensor output and pressure (output characteristic) is the origin (RP = 0,
PM = 0).

In FIG. 2, the straight line indicated by S indicates the reference characteristic. The reference characteristic S is a sensor output characteristic with respect to pressure in an ideal case where there is no error in the sensor output. However, as described above, if the oxygen concentration sensor is actually normal, its output characteristic is a straight line passing through the origin, but the output of the oxygen concentration sensor rarely completely matches the reference characteristic. And the slope of the output characteristics differs from product to product. In the oxygen concentration sensor actually used, only the variation of the output characteristic of each product within a predetermined tolerance α with respect to the reference characteristic is used. FIG.
, The tolerance α is indicated by the ratio of the deviation of the sensor output RP to the output RS in the reference characteristic when air in a standard state (oxygen concentration 21%) is measured at atmospheric pressure. That is, the output RP of the oxygen concentration sensor actually used when measuring the standard atmosphere at atmospheric pressure is always RS × (1−α) <RP <RS × (1+
α). Here, the tolerance α of the variation of the sensor is the air-fuel ratio control when the oxygen concentration sensor is used,
The maximum value is set so that the influence that occurs in the EGR control or the like is within an allowable range. That is, the slope of the actual sensor output characteristic is set to be in a range of (1 + α) times or less and (1-α) times or more of the reference characteristic.

For this reason, the output of the oxygen concentration sensor varies within the tolerance for each product, but in actual control, an operation is performed to correct the output characteristics of each sensor to match the reference characteristics, and the corrected sensor is operated. Control is performed using the output. For this correction, for example, the ratio between the output RS of the atmospheric pressure standard state in the reference characteristic and the output RP ₀ of each sensor when measuring the air in the atmospheric pressure standard state is obtained in advance, and this ratio is used as the output of each sensor. This is done by multiplying them.

That is, the output characteristic of the oxygen concentration sensor always becomes a straight line, and if the sensor is normal, the straight line of the output characteristic passes through the origin. As shown in FIG. If it is ₀ , instead of the output RP of the sensor, RP × RS / RP ₀
Is used, the output after correction matches the reference characteristic (characteristic S in FIG. 2). For this reason, as long as each control is performed using the corrected output characteristics, the variation in the output characteristics within the tolerance of each sensor product does not pose any problem in control.

In this embodiment, the presence or absence of a sensor failure is determined based on the change characteristic of the corrected oxygen concentration sensor output with respect to the pressure change, that is, the output characteristic of the corrected sensor output in FIG. That is, the change in the sensor output with respect to the pressure after the correction should match the reference characteristic shown by S in FIG. 2 by the correction. Therefore, if the corrected sensor output characteristic deviates from the reference output characteristic by a certain degree or more, it can be determined that the sensor has failed.

Next, the method of determining a failure of the intake oxygen concentration sensor of the present embodiment will be described in detail. In the following description, unless otherwise specified, the "oxygen concentration sensor output" and the "sensor output characteristic" are used. Means the output after the variation correction for each product and the change characteristic of the corrected output with respect to the pressure. FIG. 3 is a diagram illustrating a method for determining a failure of the intake oxygen concentration sensor according to the present embodiment. 3, the vertical axis represents the sensor output RP, and the horizontal axis represents the intake pressure PM. Now, it is assumed that the output of the intake oxygen concentration sensor when the intake pressure PM during engine operation is PH is RPH, and the sensor output when the intake pressure is PL (PH> PL) is RPL. Now, the coordinates (P
L is a point represented by L, RPL, and coordinates are (PH, RPH)
The point represented by is called H.

In this case, if the sensor is normal, the sensor output and the intake pressure are on a straight line passing through the origin (PM = 0, RP = 0).
It should be a straight line (straight line I in FIG. 3) connecting the origin and the points (PL, RPL). In this case, the slope KL of the output characteristic
Is KL = RPL / PL. On the other hand, the slope KHL of the two points actually measured, that is, the straight line (the straight line II in FIG. 3) connecting the point H and the point L is KHL = (RPH-RPL)
/ (PH-PL).

Therefore, if the sensor is normal, K
HL = KL, the ratio between KHL and KL, KHL / KL
Becomes 1. On the other hand, when the sensor is out of order, the value of KHL is not equal to KL because the sensor output characteristic does not become a straight line passing through the origin. At this time, the ratio between the slopes KHL and KL and the value of KHL / KL are 1
Means that the actual sensor output characteristics deviate from a straight line passing through the origin as the distance from the line increases.

In this embodiment, the ratio KHL / KL between the slopes KHL and KL is used as a characteristic value representing the sensor output characteristic. When this characteristic value is equal to or more than the upper limit value (1 + α), or when the lower limit value (1 -Β) When it is less than or equal to, it is determined that the sensor has failed. Here, α is the tolerance (α> 0) of the variation of the sensor described above for each product,
β is set to a positive value larger than α (β>α> 0). First, a characteristic value KHL for determining that the sensor is normal
The reason why the upper limit value of / KL is set equal to the tolerance of the product variation will be described.

The characteristic value KHL / KL becomes larger than 1 and the upper limit becomes a problem when the slope of the actual sensor output characteristic, that is, KHL, becomes larger than the reference output characteristic slope KL. That is, assuming that the reference output characteristic in FIG. 3 is a straight line connecting the origin and the point L, the actual sensor output characteristic connecting the point H and the point L is shown by a straight line II in FIG. Is the case. In an actual engine, the oxygen concentration in the intake air may be lower than the oxygen concentration in the atmosphere due to the purging of evaporated fuel, the execution of EGR, or the introduction of crankcase exhaust gas into the intake passage by opening the PCV valve. Oxygen concentration never exceeds standard atmosphere. For this reason, it is determined whether or not the degree of increase of the actual slope KHL of the sensor output characteristic with respect to the reference slope KL of the output characteristic can be tolerated in control, by actually purging the evaporated fuel or performing EGR. It is not necessary to consider the case where the oxygen concentration has decreased, and if only the case of the standard atmosphere where the sensor output is maximized is considered, the failure of a normal sensor is not determined. Further, as described above, the tolerance α of the variation of the sensor output is set to a maximum value within a range in which the influence of the variation on the control is allowable, based on the measurement result in the standard atmosphere. In other words, unless the actual gradient (KHL) of the sensor output characteristic is equal to or more than (1 + α) times the gradient (KL) of the reference output characteristic, the deviation of the sensor output is within the allowable range.

On the other hand, the value of the output characteristic value KHL / KL is a numerical value indicating how many times the slope of the actual sensor output characteristic is larger than the reference output characteristic. Therefore, if the upper limit of the output characteristic value is set to (1 + α), the output characteristic value KHL /
When the value of KL is smaller than the upper limit, control can be regarded as normal even if the output characteristics of the sensor deviate from the reference characteristics. For this reason, in the present embodiment, the upper limit value of the normal judgment of the output characteristic value is set to (1 + α) using the tolerance α of the variation for each product. As described above, in the present embodiment, a sensor output and an output characteristic used for determination have already been corrected for variations. Therefore, in the present embodiment, the upper limit value of the failure determination is set to be equal to the variation tolerance α, but the above determination does not determine the variation (in a normal range) of the output of each sensor. Since the basic idea of the "range that does not affect the control" simply coincides, the upper limit value is a value equal to the tolerance α.

As described above, when setting the upper limit of the normality determination of the sensor, it is sufficient to consider only the case where the intake oxygen concentration is equal to the atmosphere. However, when setting the lower limit of the normality determination, it is necessary to consider the purging of fuel vapor and the execution of EGR. That is, when the purge of the fuel vapor or the EGR is being performed, the intake oxygen concentration is actually lower than that of the atmosphere. For this reason, even when the sensor is normal, the output decreases when the evaporative fuel purge or the EGR is executed, and the slope of the reference output characteristic itself decreases.
For this reason, simply setting the lower limit equal to the variation tolerance α as in the case of the upper limit, the sensor fails when the slope of the sensor output characteristic becomes (1−α) times or less the slope of the reference output characteristic. If the determination is made, the normal sensor may be determined to be faulty.

Therefore, in the present embodiment, a value β larger than α is used as the lower limit value so as not to cause an erroneous determination even when the presence or absence of a sensor failure is determined during the purge of the evaporated fuel or during the execution of EGR. When the slope of the sensor output characteristic is equal to or less than (1−β) times the slope of the reference output characteristic, it is determined that the sensor has failed. Here, the value of β is a value in the case where an output deviation corresponding to the tolerance α further occurs based on the output characteristic of a normal sensor when the intake oxygen concentration is the lowest due to the execution of the evaporated fuel purge or the EGR. Equivalent to. As described above, the output characteristic value (KHL / KL) representing the deviation of the output characteristic of the sensor during use from the reference characteristic is calculated, and the characteristic value is compared with the upper limit value and the lower limit value set as described above, thereby evaporating. It is possible to determine the presence or absence of a sensor failure irrespective of whether fuel purge or EGR is performed, and the chances of performing the determination of the presence or absence of a sensor failure are increased, enabling early detection of sensor failure Becomes

Next, the operation of detecting a sensor failure during actual engine operation will be described. In the present embodiment, the ECU
Reference numeral 30 reads the intake pressure PH and the output RPH (point H in FIG. 3) of the intake oxygen concentration sensor 31 when the intake pressure becomes higher than the predetermined pressure PA during operation of the engine. When the pressure becomes lower than the predetermined pressure PB, the intake pressure PL and the output RPL (point L in FIG. 3) of the intake oxygen concentration sensor 31 at that time are read. Here, the pressures PA and PB are values for keeping a certain distance between the point H and the point L in FIG. 3 in order to improve the accuracy in calculating the gradient KHL of the sensor output characteristic. Any pressure can be used as long as PH> PA and PL <PB.

After reading the above PH, RPH and PL, RPL, the ECU 30 calculates the change amount of the output of the intake oxygen concentration sensor between the point H and the point L in order to calculate the characteristic value KHL / KL. RPH-RPL) and the change in intake pressure (P
H-PL) is calculated, and each is divided by the sensor output RPL and the intake pressure PL at the point L to calculate the dimensionless change ΔRP in the sensor output and the dimensionless change ΔP in the intake pressure. That is, ΔRP = (RPH−RPL) / RPL, ΔP = (PH−
PL) / PL The output characteristic value KHL / KL is given by ΔRP
/ ΔP is calculated. ΔRP / ΔP = ((RPH-RPL) / RPL) / ((PH-PL) / PL) = ((RPH-RPL) / (PH-PL)) / (RPL / PL) = KHL / KL

In this embodiment, when the value of the characteristic value KHL / KL calculated above becomes equal to or more than the upper limit value (1 + α) or equal to or less than the lower limit value (1-β), it is determined that the sensor has failed. ing. FIG. 4 is a flowchart illustrating the actual operation of the sensor failure determination operation. This operation is performed as a routine executed by the ECU 30 at regular intervals. In the operation of FIG.
It is determined whether the condition for executing the failure determination of the intake oxygen concentration sensor 31 is satisfied at present. In the present embodiment, the determination execution conditions in step 401 are that the intake pressure sensor 33 is normal and that the intake oxygen concentration sensor 31 is activated. Whether the intake pressure sensor 33 is normal or not is determined by a determination operation (not shown) separately executed by the ECU 30, for example, based on whether or not the output of the intake pressure sensor 33 before the start of the engine is near the atmospheric pressure. Whether or not the intake oxygen concentration sensor 31 is activated is determined based on whether or not the intake oxygen concentration sensor has generated an output after the engine is started.

If the determination condition is satisfied in step 401, then in step 403 the intake pressure sensor 33
It is determined whether or not the current intake pressure PM detected in step is higher than a predetermined value A. If PM> A, that is, if the intake pressure allows measurement on the high pressure side (point H in FIG. 3), the process proceeds to step 405, and is the value of the flag XH set to 1? Determine whether or not. Flag XH
Is the reading of the intake pressure on the high pressure side and the sensor output (Fig. 3
XH = 0 is set at the start of the engine, and when the measurement at the point H after the start is completed, XH =
Set to 1.

If XH ≠ 1 in step 405, the measurement on the high pressure side has not yet been completed, so in step 407 the current intake pressure sensor 33 output PM is set to PH and the intake oxygen concentration sensor 31 output RP Is stored as RPH,
In step 409, the value of the flag XH is set to 1 to indicate that the measurement on the high pressure side (point H in FIG. 3) has been completed. On the other hand, if XH = 1 in step 405, the measurement on the high pressure side has already been completed, so steps 407 and 409 are skipped. Step 403
If PM ≦ A, the current intake pressure is lower than the pressure at which measurement on the high pressure side can be performed.
The program proceeds to 1 to determine whether PM <B, that is, whether the intake pressure has decreased to a pressure at which measurement on the low pressure side (point L in FIG. 3) can be performed. If PM <B, steps 413 to 417 are executed, and if the measurement on the low pressure side has not been completed, the current intake pressure sensor 33 output PM and intake oxygen concentration sensor 31 output RP are compared. Are stored as the measurement values PL and RPL on the low pressure side, respectively, and the value of a flag XL indicating that the measurement on the low pressure side is completed is set to 1.

Then, in step 419, it is determined whether both the values of the flags XH and XL are set to "1". Here, if one or both of the flags XH and XL are not set to 1, the measurement on both the high pressure side (point H in FIG. 3) and the low pressure side (point L in FIG. 3) ends. Since the judgment has not been made, the execution of the current routine is terminated without executing the judgment operation of step 421 and subsequent steps. Step 41
If both the values of the flags XH and XL are 1 at 9, the data acquisition on both the high-pressure side and the low-pressure side has been completed, and the sensor failure determination operation of step 421 and subsequent steps is executed. .

That is, in step 421, the above-mentioned dimensionless change amount ΔP of the intake pressure is calculated by using the intake pressures PH and PL measured on the high pressure side and the low pressure side, and ΔP = (PH−P
L) / PL, and the dimensionless change amount ΔRP of the output of the intake oxygen concentration sensor is calculated by using RPH and RPL.
RP = (RPH-RPL) / RPL. In step 423, it is determined whether the value of the output characteristic value (ΔRP / ΔP) is between the upper limit value (1 + α) and the lower limit value (1-β). Is done. In addition, the output characteristic value is equal to the upper limit value (1+
If it is within the range between α) and the lower limit (1−β), the sensor is determined to be normal, and in step 425, the value of the flag XF indicating the state of the sensor is set to 0 (normal).

On the other hand, in step 423, the characteristic value (ΔPR /
ΔP) is equal to or more than the upper limit (1 + α) or the lower limit (1
-Β) If it is less than or equal to the above, the process proceeds to step 427,
The value of the flag XF is set to 1 (failure). When the value of the flag XF is set to 1, the fuel injection amount correction and the EGR control based on the output of the intake oxygen concentration sensor 31 which are separately executed by the ECU are prohibited, and the vicinity of the driver's seat is closed. The installed warning light is turned on to notify the driver that the sensor has failed. As described above, in the present embodiment, the upper limit value and the lower limit value of the sensor output characteristic value at the time of failure determination are set to appropriate values. Can be performed, and the chance of performing the sensor failure diagnosis during operation increases.

Next, the second operation of the sensor failure determination operation according to the present invention will be described.
An embodiment will be described. In the above-described embodiment, the lower limit of the determination value of the sensor failure presence or absence is set to the same value (1−β) regardless of whether the purge or the EGR is performed. The lower limit value β is set to a value larger than α in consideration of the case where the intake oxygen concentration actually decreases due to purge or EGR. However, in practice, purging and EGR
If the judgment is made when is not performed,
Conversely, the lower limit is too low, and the accuracy of failure detection may be reduced.

Therefore, in this embodiment, the data acquisition of the sensor output and the intake pressure on the high pressure side and the low pressure side is performed by purging or EG.
The lower limit value at the time of the determination is changed based on whether or not the R is performed. That is, if purge or EGR has been performed at the time of data acquisition, the lower limit value for determination is set to the same (1-β) as in the above-described embodiment.
If the data acquisition is performed when purging or EGR is not performed, the lower limit is set to the lower limit (1-α) of the variation tolerance of each sensor product. This allows
When the purge and the EGR are not performed, the determination of the presence or absence of the sensor failure is performed more accurately.

FIGS. 5 and 6 are flow charts for explaining the actual judgment operation of this embodiment. The operation in FIG.
This is performed as a routine executed by the U30 at regular intervals. In FIG. 5, a step 501 indicates a determination as to whether or not a sensor failure determination execution condition is satisfied. The determination execution conditions in step 501 are the same as those in step 401 in FIG.

Next, at step 503, it is determined whether or not the value of the flag PG is set to 1. Flag P
G is a flag that is set by an operation separately executed by the ECU 30, and is 1 if an operation that affects the intake oxygen concentration, such as purge or EGR, is currently being executed.
, And is set to 0 when not being executed. If PG ≠ 1 in step 503, that is, if purging or EGR is not currently being executed, step 505 is executed.
From step 523 (FIG. 6), the oxygen concentration sensor outputs RPH and RPL at two different intake pressures and the intake pressures PH and PL at that time are read, and when the data acquisition is completed, the dimensionless sensor output change Quantity Δ
RP and the intake pressure change amount ΔP are calculated (step 5).
23).

Steps 505 to 523 are the same operations as steps 403 to 421 in FIG.
05 to 523 are different only in that they are executed only when purging, EGR and the like are not executed. ΔR in the state where purging, EGR, etc. are not executed as described above
After calculating P and ΔP, in step 525 in FIG. 6, the output characteristic value ΔRP / ΔP calculated based on these values is compared with the upper limit value and the lower limit value in the same manner as in step 423 in FIG. It is determined whether or not is broken. In the determination in step 525, the upper limit value is the same value (1 + α) as in step 423 in FIG. 4, but the lower limit value is different from the value (1-α) in step 423 in FIG.

That is, the values of the sensor outputs RPH, RPL, PH, and PL used for the determination in step 525 are values when operations that affect the intake oxygen concentration, such as purge and EGR, are not performed. The intake oxygen concentration has a value equal to the standard atmosphere. For this reason, when setting the lower limit value, it is not necessary to consider a determination error due to EGR, purge, or the like. Therefore, the lower limit value is set based on the variation tolerance α of the sensor output for each product, similarly to the upper limit value. . This enables more accurate sensor failure determination.

On the other hand, when operations that affect the intake oxygen concentration, such as purge and EGR, are being performed in step 503, the operations of steps 531 to 549 are performed. The operations of Steps 533 to 549 are substantially the same as those of Steps 505 to 523, except that purge, E
The difference is that the operation is performed only during execution of an operation that affects the intake oxygen concentration such as GR, and in order to distinguish the acquired data from the data acquired in steps 505 to 523, the sensor output is PRPH, PRPL, Intake pressure is PP
H and PPL are stored.

XPH and XPL are flags indicating whether or not data acquisition on the high-pressure side and low-pressure side during purging has been completed, respectively.
It has the same function as L. In step 547 of FIG. 6, high-pressure side data PRP during execution of operations such as purge and EGR
It is determined whether acquisition of both H, PPH, and the low-pressure side data PRPL, PPL has been completed. If the acquisition has been completed, the process proceeds to step 549, where the dimensionless sensor output change amount and intake air The pressure change amount is calculated. Also in this case, the dimensionless change amount calculated in step 549 is stored under the names ΔPRP and ΔPP to distinguish it from the dimensionless change amount calculated in step 523.

In step 551, the output characteristic value Δ calculated based on the dimensionless change amounts ΔPRP and ΔPP
By comparing PRP / ΔPP with the upper limit value and the lower limit value, the presence or absence of a sensor failure is determined. In this case, since the determination is based on the data acquired during the execution of the purge,
As in step 423 of FIG. 4, the upper limit value in the determination is (1 + α) and the lower limit value is (1−β).

If the output characteristic value is between the upper limit value and the lower limit value, the value of the flag XF is set to 0 in step 553.
When the value is equal to or more than the upper limit value or equal to or less than the lower limit value, the value of the flag XF is set to 1 in step 555 as in steps 527 and 529. As described above, according to the present embodiment, the lower limit of the determination value in the event of a sensor failure is changed according to whether or not an operation that affects the intake oxygen concentration such as purge and EGR is being performed. By doing so, a more accurate determination of sensor failure can be made.

Next, a third embodiment of the present invention will be described. In the above-described embodiments, during execution of operations that affect the intake oxygen concentration, such as purge and EGR, taking into account these effects, the lower limit of the sensor failure determination value is set to a low value so that a normal sensor can operate normally. This prevents erroneous determination as abnormal. However, for example, when the purge amount or the EGR amount of the fuel vapor fluctuates during the execution of the determination operation, a normal sensor may be determined to be faulty with the setting of the lower limit. The sensor failure determination of the above has a possibility of causing an erroneous determination. . Here, if the determination of the presence or absence of the sensor failure is always performed in a state where the purge and the EGR are not performed, the above-described problem does not occur. However, in actual internal combustion engines for vehicles, purging or EGR is performed under most operating conditions. Therefore, if the presence or absence of a sensor failure is determined only when purging or EGR is not performed, there is an opportunity for failure detection. As a result, the sensor failure cannot be detected early. Also, when performing a sensor failure determination, purge, EGR
It is conceivable to suspend the execution of
Stopping the GR may affect the engine performance or increase the evaporative fuel emission and exhaust emission. Therefore, it is not preferable to stop the purge or EGR every time the sensor failure determination is performed.

For this reason, in this embodiment, the purge or EG
The determination is made without changing the value of the lower limit at the time of performing R. If the value of the output characteristic value based on the data acquired during the execution of the purge or EGR becomes smaller than the lower limit, the sensor has failed immediately. Instead, it is determined whether or not there is a failure under the condition that the purge and EGR are not performed again. This prevents erroneous determination that a normal sensor has failed, thereby further improving the determination accuracy.

FIG. 7 is a part of a flowchart for explaining the failure determination operation of the present embodiment. Since the failure determination operation of the present embodiment is only partially different from the determination operations of FIGS. 5 and 6, only the different parts are shown in FIG. As shown in FIG. 7, in the present embodiment, the steps shown in steps 701 to 709 are executed instead of the operations of steps 551 to 555 in FIG.

That is, acquisition of data on the high-pressure side and the low-pressure side is completed during the execution of the purge. At step 549, the dimensionless sensor output change ΔPRP and intake pressure change ΔPP are calculated, and then ΔPRP and ΔPP are calculated. Whether the sensor output characteristic value ΔPRP / ΔPP calculated using the equation (1) is smaller than the upper limit (1 + α) (step 701), and the lower limit (1-
β) is determined individually (step 705). Also in this case, in steps 701 and 705, (1-
β) <ΔPRP / ΔPP <(1 + α), the sensor is determined to be normal, and the value of the failure flag XF is 0.
If ΔPRP / ΔPP ≧ (1 + α) in step 701, it is determined that the sensor has failed, and the value of the flag XF is set to 1, as in the embodiments of FIGS. 5 and 6. is there.

However, in the embodiment shown in FIGS. 5 and 6, even when purge and EGR are executed, ΔPRP / ΔP
When P ≦ (1−β), it is immediately determined that a failure has occurred, and the value of the flag XF is set to 1 (step 529). If ΔPRP / ΔPP ≦ (1−β) in FIG. 7), the determination is suspended without immediately determining that the sensor has failed, and the purging and EGR currently being executed are stopped in step 709. To end this operation.

Thus, when the operation is executed next, steps 505 to 529 (FIGS. 5 and 6) are executed, and operations that affect the intake oxygen concentration such as purge and EGR are performed. In this state, the sensor failure determination is performed again. Therefore, an accurate output characteristic value cannot be obtained due to a change in the evaporated fuel concentration or the EGR amount at the time of purging during the execution of the determination operation.
In the case where it is determined that a failure has occurred, the determination is performed again without the influence of the purge or EGR, thereby preventing a normal sensor from being erroneously determined to have failed.

In this embodiment, if ΔPRP / ΔPP ≦ (1−β) during the purging and EGR, and the sensor is determined to be faulty, the purging, EGR, etc. are stopped and the determining operation is executed again. Therefore, the operating state of the engine is affected. However, the purging or EGR is stopped only when the sensor is determined to be faulty and when the output characteristic value falls below the lower limit value. Therefore, the probability that the purging or EGR is actually stopped is extremely low. The impact on engine performance and deterioration of emissions will be substantially negligible.

[0080]

According to the present invention, the presence or absence of a sensor failure is determined based on whether or not a change in the output of the intake oxygen concentration sensor and a change in the intake pressure satisfy a predetermined relationship during operation of the engine. Purging and EG
Even when an operation that affects the intake oxygen concentration, such as R, is performed, a common effect is provided that the presence / absence of a sensor failure can be easily and accurately determined.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to an internal combustion engine for a vehicle.

FIG. 2 is a diagram illustrating a relationship between an output of a general intake oxygen concentration sensor and intake pressure.

FIG. 3 is a diagram for explaining the principle of determining the presence or absence of a failure in the intake oxygen concentration sensor according to the embodiment of FIG. 1;

FIG. 4 is a flowchart illustrating a first embodiment of a failure determination operation of the intake oxygen concentration sensor.

FIG. 5 is a part of a flowchart illustrating a second embodiment of the failure determination operation of the intake oxygen concentration sensor.

FIG. 6 is a part of a flowchart illustrating a second embodiment of the failure determination operation of the intake oxygen concentration sensor.

FIG. 7 is a part of a flowchart illustrating a third embodiment of the failure determination operation of the intake oxygen concentration sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine main body 10 ... Intake passage 30 ... Electronic control unit (ECU) 31 ... Intake oxygen concentration sensor 33 ... Intake pressure sensor 41 ... Purge control valve 51 ... EGR control valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) F02M 25/08 F02M 25/08 Z 301 301J 301U F term (reference) 3G044 AA04 BA24 CA13 DA02 EA23 EA55 FA05 FA10 FA27 GA02 GA22 GA27 3G062 BA04 BA05 BA06 EA11 FA11 FA12 FA20 GA01 GA02 GA17 GA24 3G084 AA03 AA04 DA04 DA10 DA15 DA27 DA30 FA00 FA11 FA29 FA33 3G301 HA01 HA04 HA13 HA14 HA15 JA03 JA16 JA26 JB01 JB09 LA01 LB04 MA01

Claims (5)

[Claims] 1. A failure determination device for determining presence or absence of a failure of an intake oxygen concentration sensor that is arranged in an intake passage of an internal combustion engine and generates an output corresponding to an oxygen concentration in intake air of an engine, and detects an engine intake pressure. Intake pressure detection means, based on whether the output change amount of the intake oxygen concentration sensor with respect to the change amount of the engine intake pressure satisfies a predetermined relationship when the engine intake pressure changes, A diagnosis device for an intake oxygen concentration sensor, comprising: a determination unit configured to determine whether there is a failure. 2. The method according to claim 1, wherein the determining unit determines the output of the oxygen concentration sensor when the intake pressure detected by the intake pressure detecting unit is a first pressure and when the intake pressure is a second pressure different from the first pressure. The sensor output is stored as first and second sensor outputs, respectively, based on a ratio of a difference between the first sensor output and the second sensor output to a difference between the first pressure and the second pressure. Calculating a characteristic value representing a change characteristic with respect to the pressure, and when the calculated characteristic value is equal to or greater than a predetermined upper limit or equal to or less than a predetermined lower limit, it is determined that the intake oxygen concentration sensor has failed. A diagnostic device for an intake oxygen concentration sensor according to claim 1. 3. The upper limit value is set on the basis of an output variation tolerance of each product of the intake oxygen concentration sensor, and the lower limit value is a change amount of the intake oxygen concentration when the exhaust gas is recirculated to the engine intake or the engine intake gas. 3. The diagnostic device for an intake oxygen concentration sensor according to claim 2, wherein the diagnostic device is set based on an intake oxygen concentration change amount at the time of introducing the hydrocarbon component into the intake air or both. 4. When neither the exhaust gas recirculation to the engine intake air nor the introduction of hydrocarbon components into the engine intake air is performed, the lower limit is set to the output variation tolerance of each product of the intake oxygen concentration sensor. Claim 3 set based on
4. The diagnostic device for an intake oxygen concentration sensor according to claim 1. 5. When it is determined that the characteristic value has become less than the lower limit value and the intake oxygen concentration sensor has failed at the time of exhaust gas recirculation during engine operation or at the time of introduction of hydrocarbon components into the engine intake. When the exhaust gas recirculation to the engine intake and the introduction of the hydrocarbon component to the engine intake are not performed again, the characteristic value is calculated, and the malfunction of the intake oxygen concentration sensor based on the characteristic value is calculated. The diagnostic device for an intake oxygen concentration sensor according to claim 4, wherein the determination of presence / absence is performed.