Abnormality detection device for internal combustion engine

The present invention provides an abnormality detection device in which the fuel property sensor is disposed in a branch flow path which is such that there is a time where the fuel in the branch flow path drops out therefrom between one start of the internal combustion engine and the next start. An output value of the fuel property sensor generated when the fuel is flowing through the branch flow path is acquired as a first sensor output value. An output value of the fuel property sensor generated when the fuel in the branch flow path drops out therefrom is acquired as a second sensor output value. The first sensor output value and the second sensor output value are used as judgment data to judge whether the fuel property sensor is abnormal.

TECHNICAL FIELD

The present invention relates to an abnormality detection device for an internal combustion engine whose operation is controlled in accordance with the properties of an employed fuel, and more particularly to an abnormality detection device capable of detecting an abnormality of a fuel property sensor used for fuel property determination.

BACKGROUND ART

An internal combustion engine capable of using fuels having different properties is mounted in the so-called FFVs (flexible-fuel vehicles). Ethanol-blended gasoline may be typically used for such an FFV internal combustion engine. When ethanol-blended gasoline is used as a fuel for an internal combustion engine, it is necessary to adjust air-fuel ratio in accordance with the concentration of the ethanol in the fuel because ethanol greatly differs from gasoline in calorific value per unit volume. Therefore, internal combustion engines using ethanol-blended gasoline include an ethanol concentration sensor as a fuel property sensor in order to determine the properties of an employed fuel, more specifically, the ethanol concentration. Examples of sensors suitable for the ethanol concentration sensor are a capacitance sensor, an optical transmission sensor, and an optical refractive-index sensor.

The fuel's ethanol concentration measured by the ethanol concentration sensor is used as a parameter for the air-fuel ratio control of the internal combustion engine. This makes it possible not only to obtain a desired torque but also to ensure satisfactory emissions performance without regard to the ethanol concentration in the employed fuel.

As described above, the fuel property sensor in an FFV internal combustion engine plays an important role to ensure the expected performance of the internal combustion engine. However, there is no guarantee that the fuel property sensor functions normally at all times, as is the case with other sensors. Wiring disconnection, short-circuiting, sensor element deterioration, or other abnormality may occur in the fuel property sensor. If, in such an instance, the internal combustion engine is controlled by using output values of the fuel property sensor, the internal combustion engine would fail to operate appropriately in accordance with the properties of the employed fuel, resulting in the performance characteristics of the internal combustion engine such as emissions performance and fuel efficiency to be degraded.

It is therefore desirable that abnormality in the fuel property sensor is accurately detected so as to immediately take an appropriate remedial action such as repair or replacement. In view of the above circumstances, a technology disclosed in JP-A-2010-038052 (hereinafter referred to as Patent Document 1) presets an upper-limit threshold value and a lower-limit threshold value for the output value of an ethanol concentration sensor. When the output value is outside the range between the upper- and lower-limit threshold values, this technology concludes that the ethanol concentration sensor is malfunctioning. In addition, since the output value of the ethanol concentration sensor varies with fuel temperature even when the ethanol concentration is constant, this technology can change the upper- and lower-limit threshold values in accordance with the fuel temperature measured by a fuel temperature sensor.

However, the technology disclosed in Patent Document 1 cannot accurately detect abnormality in the ethanol concentration sensor in all cases. A phenomenon called “stuck” is an abnormality that is likely to occur particularly in the ethanol concentration sensor which greatly affects the control of the internal combustion engine. It is a phenomenon such that the output value of the ethanol concentration sensor becomes stuck at a fixed value. This phenomenon may occur even when the output value of the ethanol concentration sensor is between the upper- and lower-limit threshold values. Therefore, the technology disclosed in Patent Document 1 may fail to detect this phenomenon as an abnormality.

A method of detecting a capacitance temperature sensor being stuck is well-known as described in JP-A-2000-303898 (hereinafter referred to as Patent Document 2). The method described in Patent Document 2 calculates the difference between a maximum water temperature and a minimum water temperature, which are measured by the temperature sensor after startup of the internal combustion engine. If the calculated difference is small, this method concludes that the sensor is stuck. However, it is difficult to apply this method to the detection of an ethanol concentration sensor being stuck. The reason is that, unlike fuel temperature, ethanol concentration in fuel cannot be changed unless operation such as refueling is performed.

When the output characteristics of the ethanol concentration sensor relative to the fuel temperature are taken into account, as in the technology of Patent Document 1, whether the ethanol concentration sensor is stuck can be determined by checking whether the output value of the ethanol concentration sensor varies with the fuel temperature. However, if a fuel whose ethanol concentration is 0% is employed, the output value of the ethanol concentration sensor remains substantially unchanged even when the fuel temperature varies. Therefore, this method cannot determine whether the ethanol concentration in the employed fuel is 0% or the sensor is stuck.

Another method of detecting abnormality in the fuel property sensor is described in JP-A-2008-014741 (hereinafter referred to as Patent Document 3). The abnormality detection method described in Patent Document 3 presumes that the inlet of a fuel tank is provided with a measurement chamber including a fuel property sensor. It is also presumed that the fuel property sensor outputs signals of different levels depending on the presence/absence of fuel at a measurement space within the measurement chamber. When the employed configuration is as described above, no fuel stays in the measurement space during normal operation. Fuel temporarily stays in the measurement space when the fuel tank is being refueled. The signal level of the fuel property sensor then changes reflecting the presence of the fuel in the measurement space. Therefore, if the fuel property sensor does not output an appropriate signal during refueling, it can be concluded that the fuel property sensor is malfunctioning.

However, the technology described in Patent Document 3 has a problem in terms of accuracy in determining the properties of the employed fuel. The fuel properties required as information for controlling the internal combustion engine is the properties of the fuel supplied from the fuel tank to the internal combustion engine, or more specifically, the properties of the fuel injected from an injector. The fuel property sensor in the configuration set forth in Patent Document 3, however, performs determination based on the properties of the fuel supplied to the fuel tank and not those of the fuel injected from the injector. In FFV internal combustion engines, which can use fuels having different properties, the properties of the fuel in the fuel tank do not always match with those of a newly supplied fuel. Therefore, it is highly probable that the fuel properties determined by the fuel property sensor differ from the fuel properties of the fuel injected from an injector in the technology of Patent Document 3. It is therefore difficult to achieve appropriate air-fuel ratio control in accordance with the properties of an employed fuel.

Further, the technology described in Patent Document 3 cannot detect abnormality in the fuel property sensor with adequate accuracy, or more particularly, whether the fuel property sensor is stuck. If, for instance, the output value of the fuel property sensor is stuck at an output level indicative of absence of fuel in the measurement space, it is possible to detect the “stuck” of the fuel property sensor from the output level of the fuel property sensor during refueling. However, if the output value of the fuel property sensor is stuck at an output level indicative of presence of fuel in the measurement space, the output level would not change during refueling, and thus the fuel property sensor will be judged to be operating normally. In other words, the technology described in Patent Document 3 cannot detect a stuck sensor in such case.

As described above, the previously proposed abnormality detection technologies for fuel property sensors cannot detect abnormality in a fuel property sensor with adequate accuracy, or more particularly, cannot detect a stuck fuel property sensor with adequate accuracy.

PRIOR ART LITERATURE

Patent Documents

SUMMARY OF THE INVENTION

An object of the present invention is to accurately detect abnormality in a fuel property sensor, or more particularly, a stuck fuel property sensor in an internal combustion engine whose operation is controlled in accordance with the properties of an employed fuel. To achieve such an object, the present invention provides an abnormality detection device for an internal combustion engine configured as described below.

According to the abnormality detection device provided by the present invention, a sensor having a distinctive output characteristic, such as a capacitance sensor, an optical transmission sensor, or an optical refractive-index sensor, is used as a fuel property sensor for determining the alcohol concentration, heaviness, and other properties of an employed fuel. The output characteristic which those sensors have is such that the level of an output value differs depending on whether a liquid or a gas exists in a measurement section, and when fuel exists in the measurement section, the output value is determined in accordance with the properties of the fuel. According to the abnormality detection device provided by this invention, the fuel property sensor having the above-described output characteristic is not disposed in the primary flow path of a fuel flow path connecting a fuel pump to an injector, but is disposed in a branch flow path that is branched off from the primary fuel flow path. The branch flow path should be such that there is a time where the fuel therein flows out between a start of the internal combustion engine and the next start. Such a branch flow path may be newly provided for the abnormality detection device, or alternatively, an existing fuel flow path may be used as the branch flow path. For example, a fuel flow path for guiding fuel discharged from the primary flow path via a pressure-regulating valve can be used as the branch flow path. A fuel flow path connected to a jet pump for introducing the fuel into a suction opening of the fuel pump can also be used as the branch flow path.

In a situation where the fuel is flowing through the branch flow path in which the fuel property sensor is installed, the abnormality detection device acquires the output value of the fuel property sensor as a first sensor output value. Further, in a situation where the fuel in the branch flow path has flown out, the abnormality detection device acquires the output value of the fuel property sensor as a second sensor output value. Preferably, the first sensor output value is acquired between the actuation of the fuel pump upon the start of the internal combustion engine and the stop of the fuel pump upon the stop of the internal combustion engine: that is, during a period where the fuel pump is delivering fuel from the primary flow path to the branch flow path. Further, the second sensor output value is preferred to be acquired between the stop of the internal combustion engine and the start of the internal combustion engine: that is, during a period where the fuel pump is not delivering fuel from the primary flow path to the branch flow path.

The abnormality detection device then judges, in accordance with the first and second sensor output values, whether the fuel property sensor is normal. The judgment may be conducted by comparing the difference between the first and second sensor output values against a predetermined reference difference, and then judging whether the fuel property sensor is normal in accordance with the result of the comparison. If the difference between the first and second sensor output values is smaller than the reference difference, this method concludes that the fuel property sensor is abnormal.

An alternative method would be to compare the first sensor output value against a predetermined first threshold value, compare the second sensor output value against a predetermined second threshold value, and judge, in accordance with the results of the comparisons, whether the fuel property sensor is normal. If the first sensor output value is within an abnormal region defined by the first threshold value, or the second sensor output value is within an abnormal region defined by the second threshold value, this alternative method concludes that the fuel property sensor is abnormal.

Another alternative method would be to compare the difference between the first and second sensor output values against a predetermined reference difference, compare the first or second sensor output value against a predetermined threshold value, and judge, in accordance with the results of the comparisons, whether the fuel property sensor is normal. If the difference between the first and second sensor output values is smaller than the reference difference or either the first or second sensor output value is within an abnormal region defined by the associated threshold value, this alternative method concludes that the fuel property sensor is abnormal.

To check for abnormality, the abnormality detection device uses two sensor output values having different output levels. Therefore, even when the sensor output value is stuck at a fixed value, the abnormality detection device can accurately detect it as an abnormality. Further, the abnormality detection device is configured so that the fuel subjected to fuel property judgment by the fuel property sensor is a fuel drawn from the fuel tank by the fuel pump, as with the fuel supplied to the injector. The operation of the internal combustion engine can therefore be properly controlled when the fuel property sensor is functioning normally in accordance with the properties of the employed fuel.

If the fuel property sensor is an alcohol concentration sensor for measuring the alcohol concentration in the fuel, the following function may be added to the abnormal detection device.

The function that may be added to the abnormality detection device according to the present invention is a function of diagnosing the rationality of the alcohol concentration sensor. Usage of the above-mentioned abnormality detection method enables accurate detection of a stuck sensor. However, it should be noted that the output characteristics of a sensor may deviate even if the sensor is not stuck. In such an instance, if the output value of the alcohol concentration sensor could be verified to have no doubt according to its relationship with the output value of another sensor, it can be concluded that, at least in that relation, the output value of the alcohol concentration sensor is rational.

To be more specific, the abnormality detection device estimates the alcohol concentration in the fuel injected from the injector based on the integrated amount of fuel injected by the injector and the output value of the alcohol concentration sensor. At the same time, the abnormality detection device learns the alcohol concentration in the fuel injected from the injector by exercising air-fuel ratio feedback control in accordance with the output value of an air-fuel ratio sensor disposed in an exhaust path of the internal combustion engine. When the output value of the alcohol concentration sensor has changed due to refueling, the abnormality detection device judges whether the alcohol concentration sensor is rational by verifying whether the difference between the estimated alcohol concentration and the learned alcohol concentration is not greater than a predetermined judgment value. As far as the relationship between the output value of the air-fuel ratio sensor and the output value of the alcohol concentration sensor remains unimpaired, the difference between the estimated alcohol concentration and the learned alcohol concentration should be not greater than the judgment value.

Usage of such diagnostic method enables prompt diagnosis of the rationality of the alcohol concentration sensor. This is possible because the abnormality detection device can acquire sensor output values based on the alcohol concentration in the fuel tank by just driving the fuel pump immediately after refueling without starting the internal combustion engine.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

An abnormality detection device according to the present embodiment is applied to FFV internal combustion engines, which can use not only gasoline but also ethanol-blended gasoline.FIG. 1is a schematic diagram illustrating the configuration of a fuel supply system for such an internal combustion engine.

The fuel supply system shown inFIG. 1is configured such that a fuel pump module12is disposed inside a fuel tank10. The fuel pump module12includes a reservoir cup14containing an electrically-operated feed pump (fuel pump)16and a filter20. The fuel pressurized by the feed pump16is delivered to the filter20through a check valve18, and then forwarded to a main flow path24through a check valve22. The fuel pump module12also includes a jet pump28, which delivers the fuel outside the reservoir cup14to the inside of the reservoir cup14. Part of the fuel pressurized by the feed pump16is diverged in the filter20. The diverged portion of the pressurized fuel is supplied to the jet pump28through a jet pump flow path26. In addition, the fuel pump module12also includes a low pressure regulator (pressure-regulating valve)44and an ethanol concentration sensor (fuel property sensor)52.

The main flow path24extends out of the fuel tank10and connects with a delivery pipe30on the left bank side. This delivery pipe30is connected to a delivery pipe34on the right bank side through a communication flow path32. Four injectors36are connected to each of the delivery pipes30,34for the cylinders of each bank. The pressurized fuel delivered from the feed pump16is supplied to the delivery pipe30through the main flow path24and then injected into each cylinder on the left bank by the injectors36. The pressurized fuel is also supplied from the delivery pipe30to the delivery pipe34through the communication flow path32and injected into each cylinder on the right bank by the injectors36. In the present embodiment, the fuel flow path from the discharge port of the feed pump16to each injector36, that is, the fuel flow path constituted by the filter20, the main flow path24, the delivery pipe30, the communication flow path32, and the delivery pipe34, corresponds to “the primary flow path of the fuel flow path” in the present invention.

The trailing end of the delivery pipe34is connected to a first return flow path38extending into the fuel tank10. The first return flow path38is provided with a high pressure regulator42. The high pressure regulator42automatically opens when the pressure of fuel in the delivery pipe34becomes higher than a predetermined high relief pressure and automatically closes when the fuel pressure becomes not higher than the high relief pressure. This allows the interior of the primary flow path of the fuel flow path, the path between the discharge port of the feed pump16and each injector36, to be adjusted to a predetermined high pressure defined by the high relief pressure. As the high pressure regulator42opens, fuel is discharged into the first return flow path38and the fuel returns to the fuel tank10therethrough.

A second return flow path40branches off from the main flow path24. The second return flow path40extends into the fuel tank10. The aforementioned low pressure regulator44is disposed in the second return flow path40. The low pressure regulator44automatically opens when the fuel pressure in the main flow path24becomes higher than a predetermined low relief pressure and automatically closes when the fuel pressure becomes not higher than the low relief pressure. This allows the interior of the primary flow path of the fuel flow path, the path between the discharge port of the feed pump16and each injector36, to be adjusted to a predetermined low pressure defined by the low relief pressure. As the low pressure regulator44opens, part of the pressurized fuel pumped from the feed pump16returns to the fuel tank10through the second return flow path40.

A fuel pressure selector valve46is disposed upstream of the low pressure regulator44in the second return flow path40. While the fuel pressure selector valve46is open, the fuel pressure in the main flow path24is exerted on the low pressure regulator44. The low pressure regulator44thus functions in preference to the high pressure regulator42so that the fuel pressure in the primary flow path of the fuel flow path between the discharge port of the feed pump16and each injector36is adjusted to the low pressure. In this instance, no fuel is discharged to the first return flow path38because the high pressure regulator42remains closed. On the other hand, while the fuel pressure selector valve46is closed, the fuel pressure in the main flow path24is not exerted on the low pressure regulator44and the low pressure regulator44does not function. The fuel pressure in the primary flow path of the fuel flow path between the discharge port of the feed pump16and each injector36is therefore adjusted to the high pressure by the high pressure regulator.

The ethanol concentration sensor52is disposed downstream of the low pressure regulator44in the second return flow path40. The ethanol concentration sensor52used in this embodiment is a capacitance sensor. The output value of the ethanol concentration sensor52continuously varies with the concentration of ethanol. Therefore, the ethanol concentration in the employed fuel can be measured from the output value of the ethanol concentration sensor52. The output value of the ethanol concentration sensor52is input into an ECU50to be used as information for controlling operation of the internal combustion engine. According to the configuration of the fuel supply system of this embodiment, the fuel subjected to the ethanol concentration judgment by the ethanol concentration sensor52is a fuel drawn from the fuel tank10by the feed pump16as with the fuel supplied to the injectors36. Therefore, when the ethanol concentration sensor52is operating normally, the operation of the internal combustion engine can be properly controlled in accordance with the ethanol concentration in the employed fuel.

The ECU50functions not only as a control device for controlling the operation of the internal combustion engine but also as the abnormality detection device for the internal combustion engine. When the ECU50functions as the abnormality detection device, detecting abnormality in the ethanol concentration sensor52, which is a detecting item, is performed. An abnormality detection program incorporated in the ECU50utilizes an output characteristic of the ethanol concentration sensor52to check for abnormalities. The output characteristic utilized by the program is such that the level of an output value of the sensor differs depending on whether a liquid or a gas exists between the electrodes forming the measurement section. This output characteristic is peculiar to capacitance sensors. According to such output characteristic, when the ethanol concentration sensor52is operating normally, the sensor output value should vary between cases where fuel exists and doesn't exist between the electrodes of the ethanol concentration sensor52. Therefore, whether the ethanol concentration sensor52is normally operating can be determined by comparing a sensor output value generated when fuel exists between the electrodes against a sensor output value generated when no fuel exists between the electrodes, and checking whether there is a definite difference between the compared sensor output values. If there is no difference between the compared sensor output values, it can be concluded that the ethanol concentration sensor52is abnormal, or more specifically, stuck.

To exercise the above-described abnormality judgment method, it is necessary to create a state where fuel exists between the electrodes of the ethanol concentration sensor52and a state where fuel does not exist at that section. According to the configuration of the fuel supply system for the present embodiment, such states do not need to be intentionally created because they are naturally created during normal vehicle driving.

The state where a fuel exists between the electrodes of the ethanol concentration sensor52is created while the feed pump16is operating. The fuel pressure selector valve46is open by default. Therefore, when the feed pump16operates to raise the fuel pressure, the low pressure regulator44opens to let the fuel flow to the position at which the ethanol concentration sensor52is installed. The feed pump16operates while the internal combustion engine is operated, that is, from the turning on of the ignition switch to the turning off of the ignition switch.

On the other hand, the state where no fuel exists between the electrodes of the ethanol concentration sensor52is created by turning off the ignition switch to stop the feed pump16. When the feed pump16stops to lower the fuel pressure, the low pressure regulator44closes. Then, in the downstream of the low pressure regulator44, the fuel in the second return flow path40flows out to empty the path40, and the electrodes of the ethanol concentration sensor52are exposed to air.

As described above, according to the configuration of the fuel supply system for this embodiment, the data needed for abnormality judgment of the ethanol concentration sensor52can be obtained by acquiring the output values of the ethanol concentration sensor52of when the ignition switch is on and off. Thus, the ECU50as the abnormality detection device executes an abnormality judgment process in accordance with a routine shown in the flowchart ofFIG. 2.

The routine shown inFIG. 2is executed each time the ignition switch is turned on to start the internal combustion engine. In step S102, which is the first step, the output value of the ethanol concentration sensor52is acquired when a certain amount of time has elapsed after internal combustion engine startup. The certain amount of time is a time sufficient for raising the fuel pressure so as to open the low pressure regulator44. The sensor output value acquired here would be a sensor output value indicating presence of fuel between the electrodes of the ethanol concentration sensor52(“a first sensor output value” according to the present invention). This sensor output value is hereinafter referred to as a sensor output value A.

In the next step, step S104, it is judged whether the ignition switch is off. This judgment step is repeatedly performed at fixed intervals until the ignition switch is turned off.

In step S106, which is the next step of the step where the ignition switch is off, the output value of the ethanol concentration sensor52is acquired when a certain amount of time has elapsed after the ignition switch is turned off. The certain amount of time is a time sufficient for lowering the fuel pressure so as to close the low pressure regulator44and expel the fuel from the inside of the second return flow path40. The sensor output value acquired here would be a sensor output value indicating absence of fuel between the electrodes of the ethanol concentration sensor52(“a second sensor output value” according to the present invention). This sensor output value is hereinafter referred to as a sensor output value B.

Next, in step S108, the difference between the sensor output value A and sensor output value B is calculated, and the calculated difference is calculated against a predetermined reference difference α. The reference difference α is determined based on a presumed difference between sensor output values A and B that should be measured when the ethanol concentration sensor52is operating normally. When the ethanol concentration sensor52is operating normally, the difference between sensor output values A and B varies with the ethanol concentration in the fuel. More specifically, the difference between sensor output values A and B is minimized when the ethanol concentration is 0%. Hence, the reference difference α is set with reference to a gasoline having an ethanol concentration of 0%.

If the result of comparison in step S108indicates that the difference between sensor output values A and B is greater than the reference difference α, it is concluded in step S110that the ethanol concentration sensor52is functioning normally. If, on the other hand, the difference between sensor output values A and B is not greater than the reference difference α, it is concluded in step S112that the ethanol concentration sensor52is abnormal, or more specifically, stuck.

As described above, the abnormality judgment process performed in this embodiment uses two sensor output values A and B that should have different output levels, as data for abnormality judgment. When the output value of the ethanol concentration sensor52is stuck at a fixed value, the stuck state is accurately detected as an abnormality.

Second Embodiment

A second embodiment of the present invention will now be described with reference to the accompanying drawings.

As with the abnormality detection device according to the first embodiment, the abnormality detection device according to the present embodiment is applied to an internal combustion engine having the fuel supply system shown inFIG. 1. Therefore, the subsequent description is based on the system shown inFIG. 1, as with the first embodiment.

The present embodiment differs from the first embodiment in the functionality of the ECU50as the abnormality detection device. More specifically, these two embodiments differ in the method of checking for an abnormality in the ethanol concentration sensor52. The flowchart ofFIG. 3shows a routine of abnormality judgment process executed by the ECU50in the present embodiment. This routine will be explained below.

According to the routine shown inFIG. 3, first, in step S202, the output value of the ethanol concentration sensor52is acquired when a certain amount of time has elapsed after internal combustion engine startup (sensor output value A). Next, in step S204, it is judged whether the ignition switch is off. In step S206, which is the next step of the step where the ignition switch is off, the output value of the ethanol concentration sensor52is acquired when a certain amount of time has elapsed after the ignition switch is turned off (sensor output value B). The processing steps described so far are the same as those in the first embodiment.

Next, in step S208, the sensor output value A is compared against a threshold value β (“a first threshold value” according to the present invention) and the sensor output value B is compared against a threshold value γ (“a second threshold value” according to the present invention). The threshold value β is set with reference to the minimum value of a normal sensor output value generated when fuel exists between the electrodes of the ethanol concentration sensor52. The threshold value γ is set with reference to a normal sensor output value generated when air exists between the electrodes of the ethanol concentration sensor52.

If the judgment result obtained in step S208indicates that the sensor output value A is greater than the threshold value β and that the sensor output value B is smaller than the threshold value γ, it is concluded in step S210that the ethanol concentration sensor52is normal. If, on the other hand, the sensor output value A is not greater than the threshold value β or the sensor output value B is not smaller than the threshold value γ, it is concluded in step S212that the ethanol concentration sensor52is abnormal, or more specifically, stuck.

According to the abnormality judgment process performed in the present embodiment, the validity of each of the two sensor output values A and B is examined. This makes it possible to detect abnormality in the ethanol concentration sensor52with higher accuracy compared to the abnormality judgment process performed in the first embodiment.

Third Embodiment

The abnormality detection device according to the present embodiment is characterized by the configuration of the fuel supply system to which the abnormality detection device is applied.FIG. 4is a schematic diagram illustrating the configuration of the fuel supply system for an internal combustion engine to which the abnormality detection device according to this embodiment is applied. InFIG. 4, elements identical with those of the fuel supply system shown inFIG. 1are designated by the same reference numerals.

This embodiment differs from the first embodiment in the location of the ethanol concentration sensor. In this embodiment, the ethanol concentration sensor54is disposed in the jet pump flow path26in the fuel pump module12. While the ignition switch is on and the feed pump16is operating, part of the pressurized fuel pumped from the feed pump16flows into the jet pump flow path26. This creates a state where fuel exists between the electrodes of the ethanol concentration sensor54. On the other hand, when the ignition switch is turned off to stop the feed pump16, fuel flow into the jet pump flow path26stops and the jet pump flow path26is soon naturally emptied of the fuel by the action of gravity. This creates a state where no fuel exists between the electrodes of the ethanol concentration sensor54.

Hence, according to the configuration of the fuel supply system of this embodiment, information required for abnormality judgment of the ethanol concentration sensor54can be obtained by acquiring the output values of the ethanol concentration sensor54of when the ignition switch is on and off. As specific steps of the abnormality judgment process executed by ECU50, the steps shown in the flowchart ofFIG. 2or the steps shown in the flowchart ofFIG. 3may be adopted.

Fourth Embodiment

The abnormality detection device according to the fourth embodiment is characterized by the configuration of the fuel supply system to which the abnormality detection device is applied.FIG. 5is a schematic diagram illustrating the configuration of the fuel supply system for an internal combustion engine to which the abnormality detection device according to this embodiment is applied. InFIG. 5, elements identical with those of the fuel supply system shown inFIG. 1are designated by the same reference numerals.

This embodiment differs from the first embodiment in the location of the ethanol concentration sensor. In this embodiment, the ethanol concentration sensor56is disposed in the first return flow path38. The flow of fuel in the first return flow path38is determined depending on whether the fuel pressure selector valve46is opened or closed. While the fuel pressure selector valve46is closed, the high pressure regulator42opens to let fuel flow into the first return flow path38. This creates a state where fuel exists between the electrodes of the ethanol concentration sensor56. On the other hand, while the fuel pressure selector valve46is opened, the low pressure regulator44opens to leave the high pressure regulator42closed. The fuel in the first return flow path38then naturally flows out by the action of gravity to create a state where no fuel exists between the electrodes of the ethanol concentration sensor56.

Hence, according to the configuration of the fuel supply system for this embodiment, the data required for abnormality judgment of the ethanol concentration sensor52can be obtained by acquiring the output values of the ethanol concentration sensor56of when the fuel pressure selector valve46is opened and closed. In the present embodiment, therefore, the ECU50as the abnormality detection device performs an abnormality judgment process in accordance with a routine shown in the flowchart ofFIG. 6.

The routine shown inFIG. 6is executed each time the ignition switch is turned on to start the internal combustion engine. In step S302, which is the first step, the output value of the ethanol concentration sensor56is acquired when a certain amount of time has elapsed after internal combustion engine startup. The certain amount of time is a time sufficient for raising the fuel pressure so as to open the low pressure regulator44. Since the fuel pressure selector valve46is opened by default, the low pressure regulator44opens first of the two pressure regulators42,44. The sensor output value acquired in this instance would be a sensor output value indicating absence of fuel between the electrodes of the ethanol concentration sensor56(“the second sensor output value” according to the present invention). This sensor output value is hereinafter referred to as a sensor output value B.

Next, in step S304, it is judged whether the fuel pressure selector valve46is closed. The fuel pressure selector valve46switches between an open state and a closed state in accordance with the operating conditions of the internal combustion engine such as the load and revolving speed. The judgment in step S304is performed at fixed intervals until the fuel pressure selector valve46closes.

In step S306, which is the next step of the step where the fuel selector valve46is closed, the output value of the ethanol concentration sensor56is acquired when a certain amount of time has elapsed after closure of the fuel pressure selector valve46. The certain amount of time is a time sufficient for raising the fuel pressure so as to open the high pressure regulator42and introduce the fuel into the first return flow path38. The sensor output value acquired in this instance would be a value indicating presence of fuel between the electrodes of the ethanol concentration sensor56(“the first sensor output value” according to the present invention). This sensor output value is hereinafter referred to as a sensor output value A.

In the following step, step S308, the difference between the sensor output value A and sensor output value B is calculated, and is compared against the predetermined reference difference α. The reference difference α is determined as described in connection with the first embodiment.

If the result of comparison in step S308indicates that the difference between sensor output values A and B is greater than the reference difference α, it is concluded in step S310that the ethanol concentration sensor56is normal. If, on the other hand, the difference between sensor output values A and B is not greater than the reference difference α, it is concluded in step S312that the ethanol concentration sensor56is abnormal, or more specifically, stuck.

The judgment method of step S308may be substituted by the judgment method of step S208in the routine shown inFIG. 3. More specifically, comparing the sensor output value A against the threshold value β and comparing the sensor output value B against the threshold value γ are allowable. In this case, if the sensor output value A is greater than the threshold value β and the sensor output value B is smaller than the threshold value γ, it can be concluded that the ethanol concentration sensor56is normal. If, on the other hand, the sensor output value A is not greater than the threshold value β or the sensor output value B is not smaller than the threshold value γ, it can be concluded that the ethanol concentration sensor56is abnormal.

Fifth Embodiment

As with the abnormality detection device according to the first embodiment, the abnormality detection device according to the present embodiment is applied to an internal combustion engine having the fuel supply system shown inFIG. 1. Therefore, the subsequent description is based on the system shown inFIG. 1, as with the first embodiment.

The present embodiment differs from the first embodiment in that a function of a rationality diagnostic device is added to the ECU50. The first embodiment makes it possible to accurately detect whether the ethanol concentration sensor52is stuck. However, even when the ethanol concentration sensor52is found to be not stuck, it cannot be ensured that the output characteristics of the ethanol concentration sensor52are unchanged. The output characteristics of a capacitance sensor such as the ethanol concentration sensor52may change due to foreign matter deposited between the electrodes, a corroded electrode surface, or a chipped electrode. In the present embodiment, whether the output characteristics of the ethanol concentration sensor52are changed is determined in accordance with the relationship to the output value of another sensor. The another sensor utilized in the present embodiment is an air-fuel ratio sensor (not shown) disposed in an exhaust path of the internal combustion engine.

FIG. 7shows the process of control during a startup in an internal combustion engine having the fuel supply system shown inFIG. 1. The uppermost chart ofFIG. 7shows temporal changes in the integrated amount of fuel injected from each injector36after internal combustion engine startup. The second chart ofFIG. 7shows temporal changes in the output value of the ethanol concentration sensor52in a case where refueling had been performed while the internal combustion engine was stopped. This is based on the assumption that the ethanol concentration in the fuel stored in the fuel tank10is changed due to refueling. According to the configuration of the fuel supply system shown inFIG. 1, changes in the ethanol concentration in the fuel are reflected in the output value of the ethanol concentration sensor52immediately after the feed pump16operates.

If the integrated amount of injected fuel and the output value of the ethanol concentration sensor52can be acquired, the ethanol concentration in the fuel injected from the injectors36, that is, the ethanol concentration in the delivery pipes, can be estimated by considering the cubic capacity of the fuel flow path between the fuel tank10and each injector36. The third chart ofFIG. 7shows temporal changes in the estimated ethanol concentration in the delivery pipes. Referring to this chart, the time lag d1between the change in the output value of the ethanol concentration sensor52and the beginning of the change in the estimated ethanol concentration in the delivery pipes represents the time through which an amount of fuel equivalent to the cubic capacity of the main flow path24is consumed. The time lag d2from the beginning of the change in the estimated ethanol concentration in the delivery pipes to the end of the change represents the time through which the fuel in the delivery pipes30,34is completely replaced.

Meanwhile, the aforementioned air-fuel ratio sensor is employed for air-fuel ratio feedback control which is exercised to achieve a target air-fuel ratio. In air-fuel ratio feedback control in an FFV internal combustion engine, the ethanol concentration of the employed fuel is learned in accordance with the deviation between the target air-fuel ratio and the actual air-fuel ratio estimated from the output value of the air-fuel ratio sensor. The fourth chart ofFIG. 7shows temporal changes in the learned value of the ethanol concentration. The learned value varies stepwise since the ethanol concentration is learned at fixed intervals.

If there is no change in the output characteristics of the ethanol concentration sensor52, the ethanol concentration estimated based on the output value of the ethanol concentration sensor52should substantially agree with the ethanol concentration learned based on the output value of the air-fuel ratio sensor. The lowest chart ofFIG. 7shows temporal changes in the deviation between the estimated ethanol concentration and the learned ethanol concentration. This chart indicates that the deviation is within the range of plus and minus ε. If ε is the permissible limit value of an error and the deviation is greater than ε, it can be concluded that the output value of the ethanol concentration sensor52is in doubt, namely, the ethanol concentration sensor52has lost its rationality.

The routine shown inFIG. 8is a rationality judgment process routine that is executed by the ECU50in this embodiment. This routine is executed each time the ignition switch is turned on to start the internal combustion engine. The routine will be described below.

According to the routine shown inFIG. 8, In step S402, it is judged whether the output value of the ethanol concentration sensor52has changed. If the output value has not changed, there is no possibility that a fuel having a different ethanol concentration was supplied to the internal combustion engine while it was stopped. In this case, therefore, the routine then terminates.

If the output value of the ethanol concentration sensor52has changed, in step S404, it is judged whether a predetermined refueling condition is met. The refueling condition is a condition that proves that refueling was performed while the internal combustion engine was being stopped. For example, the refueling condition may be an increase in the amount of fuel remaining in the fuel tank10measured by a remaining fuel amount sensor, or detection of fuel cap opening by a sensor or switch. If the refueling condition is not met although the output value of the ethanol concentration sensor52has changed, there may be a problem that is not to be detected by the routine. In this case, therefore, the routine terminates.

If the output value of the ethanol concentration sensor52is changed and the refueling condition is met, the process of step S406is performed. In step S406, the integrated amount of fuel injected from the injectors36is calculated. Then, in step S408, it is judged whether the integrated amount of injected fuel is larger than the cubic capacity of the main flow path24(fuel pipe cubic capacity). This judgment step is performed to verify whether a fuel whose ethanol concentration is changed due to refueling has reached the delivery pipe30. Step S406is repeatedly performed at predetermined time intervals until the condition in step S408is met.

If the condition in step S408is met, each process of steps S410and S412is performed. In step S410, an estimated value of the ethanol concentration in the delivery pipes at that moment is calculated by using the integrated amount of injected fuel and the output value of the ethanol concentration sensor52. In step S412, the learned ethanol concentration value that has been learned based on the deviation between the target air-fuel ratio and the actual air-fuel ratio estimated from the output value of the air-fuel ratio sensor is acquired from a memory.

Next in step S414, the deviation between the estimated ethanol concentration in the delivery pipes calculated in step S410and the learned ethanol concentration acquired in step S412is calculated, and then it is judged whether the deviation is smaller than the permissible limit value ε of an error. If the deviation is not greater than ε, judgment of step S416is carried out. In step S416, it is judged whether the integrated amount of injected fuel is greater than the sum of the fuel pipe cubic capacity and a capacity obtained by multiplying the delivery pipe cubic capacity by a predetermined factor “k”. The factor “k” is set to two or a greater value, for example, three. This judgment step is performed to verify that the fuel in the delivery pipes30,34is entirely replaced by the newly added fuel. Steps S406to S414are repeatedly performed at predetermined time intervals until the condition in step S416is met. If the condition in step S416is met while the deviation between the estimated ethanol concentration in the delivery pipes and the learned ethanol concentration is not greater than ε, it is concluded that the ethanol concentration sensor52is rational and then the routine is terminated.

If, on the other hand, the deviation between the estimated ethanol concentration in the delivery pipes and the learned ethanol concentration exceeds ε before the condition in step S416is met, the ECU50proceeds to step S418instead of proceeding to step S416. In step S418, it is concluded that the ethanol concentration sensor52has lost its rationality and then the routine is terminated.

Performing the rationality judgment process in this embodiment makes it possible to promptly diagnose the rationality of the ethanol concentration sensor52. This can be achieved because the configuration of the fuel supply system for this embodiment enables a sensor output value based on the ethanol concentration in the fuel tank10to be acquired by just driving the feed pump16immediately after refueling without starting the internal combustion engine. Further, the same holds true for the configuration of the fuel supply system shown inFIG. 4. Therefore, the above-described rationality judgment method can also be applied to rationality diagnosis for the ethanol concentration sensor54of the fuel supply system shown inFIG. 4.

Others

While the present invention has been described in conjunction with the foregoing embodiments, it should be understood that the present invention is not limited to the foregoing embodiments. The foregoing embodiments may be variously modified to implement the present invention without departing from the spirit and scope thereof.

For example, when the fuel pressure selector valve46closes before the ignition switch is turned off in the abnormality judgment process according to the first embodiment, the output value of the ethanol concentration sensor52may be acquired as a sensor output value B without waiting until the ignition switch is turned off. This is possible because as the fuel pressure selector valve46closes, the low pressure regulator44closes to create a state where no fuel exists between the electrodes of the ethanol concentration sensor52.

Further, the two threshold values β, γ used in the abnormality judgment process according to the second embodiment may be identical with each other. In such case, the threshold value should be a value that can clearly distinguish the sensor output value of when fuel exists between the electrodes of the ethanol concentration sensor and the sensor output value of when air exists between the electrodes of the ethanol concentration sensor.

Furthermore, although the foregoing embodiments employ an electrically-operated fuel pump, a mechanical fuel pump driven by the internal combustion engine may alternatively be used. It should be noted that the present invention can also be applied to fuel supply systems that do not have a fuel pressure selector valve and include only one type of pressure regulator.

Although the foregoing embodiments use an ethanol concentration sensor as the fuel property sensor, the type of sensor to be used may be determined in accordance with the employed fuel. If, for instance, the quality of gasoline used in the gasoline engine is to vary, a sensor for judging whether the fuel is heavy or light or a sensor for determining the octane number may be used as the fuel property sensor. Moreover, the fuel property sensor for the present invention is not limited to a capacitance sensor. Sensors other than a capacitance sensor such as an optical refractive-index sensor may also be used as the fuel property sensor as far as they have an output characteristic similar to that described herein.

DESCRIPTION OF REFERENCE NUMERALS