WO2014163046A1 - Bi-fuel diagnosis device and bi-fuel diagnosis method - Google Patents

Abstract

A bi-fuel diagnosis device equipped with: a gasoline supply device that supplies gasoline to an engine; a catalyst for purifying the gas generated after the gasoline has burned; a sensor for activating the catalyst; a CNG supply device that liquefies CNG and supplies the liquefied CNG to the engine; an operation switching means that switches between a gasoline operation, wherein the gasoline supply device is used to operate the engine, and a CNG operation, wherein the CNG supply device is used to operate the engine; a diagnosis means that performs a diagnosis on the sensor itself, and/or uses the output from the sensor to perform a diagnosis on the catalyst, and/or uses the output from the sensor to perform a diagnosis on an exhaust aftertreatment system, during the gasoline operation; and an operation stopping means that stops the operation of the diagnosis means during the CNG operation.

Description

Bi-fuel diagnostic device and bi-fuel diagnostic method

The present invention relates to a bifuel diagnostic apparatus and a bifuel diagnostic method.

2. Description of the Related Art As disclosed in JP7-1119554A, a bi-fuel diagnosis device that performs failure diagnosis of an air-fuel ratio sensor provided in an exhaust passage is known.

By the way, in a gasoline engine using a gasoline supply device, in addition to diagnosing parts necessary for operating the engine, diagnosis of the sensor itself for activating the catalyst and diagnosis of the catalyst using the sensor output are performed. When a CNG supply device is added to such a gasoline engine to configure a bi-fuel, the inventor has newly found that the sensor outputs an incorrect output during CNG operation in which the engine is operated using the CNG supply device. It was. For this reason, if the diagnosis of the sensor itself, the diagnosis of the catalyst using the sensor output, and the diagnosis of the exhaust aftertreatment system using the sensor output are continued even during the CNG operation, The reliability of each diagnosis may be reduced.

Accordingly, the present invention provides a bi-fuel diagnostic device and a bi-fuel diagnostic device that can prevent the reliability of the diagnosis of the sensor itself, the diagnosis of the catalyst using the sensor output, and the diagnosis of the exhaust aftertreatment system using the sensor output from being deteriorated. It aims at providing the diagnostic method of a fuel.

According to another aspect of the present invention, there is provided a bifuel diagnostic apparatus comprising: a gasoline supply device for supplying gasoline to an engine; a catalyst for purifying gas after the gasoline burns; a sensor for operating the catalyst; Switching means for switching between a CNG supply device that liquefies and supplies the engine to the engine, a gasoline operation that operates the engine using the gasoline supply device, and a CNG operation that operates the engine using the CNG supply device And diagnostic means for performing at least one diagnosis among the diagnosis of the sensor itself, the diagnosis of the catalyst using the output of the sensor, and the diagnosis of the exhaust aftertreatment system using the output of the sensor during the gasoline operation And an operation stop means for stopping the operation of the diagnosis means during the CNG operation.

According to another aspect of the present invention, there is provided a bifuel diagnosis method comprising: a gasoline operation for operating the engine using a gasoline supply device for supplying gasoline to the engine; and a CNG supply device for liquefying CNG and supplying the liquefied CNG to the engine. Switching between CNG operation for operating the engine and using the diagnosis of the sensor itself for working the catalyst for purifying the gas after the gasoline burns during the gasoline operation, the catalyst using the output of the sensor And at least one diagnosis of the exhaust aftertreatment system using the output of the sensor, and the diagnosis performed during the gasoline operation is stopped during the CNG operation.

FIG. 1 is a schematic configuration diagram of a bi-fuel according to the first embodiment. FIG. 2 is a timing chart for explaining diagnosis of the O ₂ sensor during gasoline operation. FIG. 3 is a timing chart for explaining diagnosis of the three-way catalyst during gasoline operation. FIG. 4 is a timing chart showing changes in the CNG operation flag, the second diagnosis permission flag, the second diagnosis flag, and the air-fuel ratio learning value from the cold start when the fuel select switch is pressed. FIG. 5 is a flowchart for explaining the setting of the CNG operation flag, the first diagnosis permission flag, and the second diagnosis permission flag. FIG. 6 is a timing chart for explaining diagnosis of the air-fuel ratio sensor of the second embodiment. FIG. 7 is a timing chart for explaining the setting of the second diagnosis flag of the second embodiment. FIG. 8 is a timing chart for explaining diagnosis of the O ₂ sensor of the third embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a schematic configuration diagram of a bi-fuel 1 according to the first embodiment. The bi-fuel 1 is configured by adding a CNG supply device 31 to an engine 2 that is a gasoline engine. The term bi-fuel generally refers to a single engine that operates by switching between two types of fuel. In each embodiment, a single engine that is specifically limited to two types of fuel, gasoline and CNG, that is, is operated by switching between gasoline and CNG, is defined as “bi-fuel 1” (Bi-Fuel).

Bi-fuel 1 requires a control unit for CNG in addition to an engine control unit for gasoline. In order to distinguish the two control units, the engine control unit for gasoline is hereinafter referred to as “gasoline control unit 11”, and the control unit for CNG is referred to as “CNG control unit 51”.

The throttle valve 17 which is an electronically controlled throttle valve is provided in the intake passage 3 of the engine 2. The opening degree of the throttle valve 17 is controlled by a throttle motor 18. The opening degree of the throttle valve 17 is detected by a throttle sensor (not shown) and input to the gasoline control unit 11. The air whose flow rate is adjusted by the throttle valve 17 flows into the combustion chamber 6.

The fuel injection valve 4 is provided in each intake port of the intake passage 3. Gasoline as fuel is intermittently injected and supplied from the fuel injection valve 4. The air flowing into the combustion chamber 6 is mixed with gasoline to form an air-fuel mixture. The fuel injection valve 4 may be provided facing the combustion chamber 6. A gasoline supply device that supplies gasoline to the engine 2 is mainly composed of a gasoline tank (not shown), a pump that pumps gasoline from the gasoline tank, a fuel injection valve 4, and the like. In each embodiment, the fuel injection valve 4 represents a gasoline supply device.

The air-fuel mixture in the combustion chamber 6 is burned by spark ignition by an ignition device 5 provided on the ceiling of the combustion chamber 6. The pressure of the gas generated by this combustion pushes down the piston 7. The vertical movement of the piston 7 is converted into the rotational movement of the crankshaft 8, and power is extracted from the crankshaft 8.

The gasoline control unit 11 receives an accelerator opening (accelerator pedal depression amount) signal from the accelerator sensor 12, a crank angle signal from the crank angle sensor 13, and an intake air amount Qa signal from the air flow meter 14. The From the signal of the crank angle sensor 13, the rotational speed Ne of the engine 2 is calculated. The gasoline control unit 11 calculates a target intake air amount and a target fuel injection amount based on these signals. Then, a command is issued to the throttle motor 18 and the fuel injection valve 4 so that the target intake air amount and the target fuel injection amount can be obtained.

The gas after the power is taken out is discharged to the exhaust passage 9. Exhaust gas (exhaust gas) contains harmful three components (HC, CO, NOx). For this reason, the exhaust passage 9 is provided with a catalyst 10 for purifying the gas after gasoline is burned. Specifically, the catalyst 10 is a three-way catalyst for purifying these harmful three components. A sensor 15, which is an air-fuel ratio sensor whose output changes linearly according to the air-fuel ratio, is upstream of the catalyst 10, and an O ₂ sensor whose output value is binary-changed at the boundary of the theoretical air-fuel ratio downstream of the catalyst 10. The sensor 16 is provided as a sensor for operating the catalyst 10.

When the catalyst 10 operates the engine 2 using gasoline as fuel (hereinafter referred to as “gasoline operation”), the exhaust air-fuel ratio fluctuates within a predetermined range centering on the theoretical air-fuel ratio of gasoline as fuel. In addition, the three harmful components are made harmless at the same time. A predetermined range centered on the theoretical air-fuel ratio is called a window. For this reason, the gasoline control unit 11 performs feedback control of the air-fuel ratio so that the air-fuel ratio of the exhaust falls within the window. Specifically, based on the intake air amount Qa detected by the air flow meter 14 and the engine rotational speed Ne detected by the crank angle sensor 13 so that a mixture of the stoichiometric air-fuel ratio of gasoline is obtained during gasoline operation. The basic injection pulse width Tp1 [ms] is calculated. This is expressed by the following equation.

Tp1 = K1 × Qa / Ne (1)
However, when the air-fuel ratio of K1: constant exhaust falls within the window, the O ₂ storage amount of the catalyst 10 is maintained at a predetermined value that is neither 0% nor 100%. The gasoline control unit 11 calculates the O ₂ storage amount [%] of the catalyst 10 based on the outputs of the sensors 15 and 16, and the calculated O ₂ storage amount is empty so as to coincide with a target value (for example, 50%). A fuel ratio feedback correction coefficient α [anonymous number] is calculated. Then, the fuel injection pulse width Ti1 [ms] is calculated by multiplying the basic injection pulse width Tp1 by the air-fuel ratio feedback correction coefficient α, and the fuel injection valve for gasoline fuel is used for the period of Ti1 at a predetermined fuel injection timing. Open 4

The fuel injection pulse width Ti1 of the injection performed by the gasoline fuel injection valve 4 during sequential injection is expressed by the following formula.

Ti1 = Tp1 × (α + αm−1) × 2 + Ts (2)
However, Tp1: Basic injection pulse width during gasoline operation,
α: Air-fuel ratio feedback correction coefficient,
αm: Air-fuel ratio learning value [anonymous number]
Ts: Invalid injection pulse width [ms],
The air-fuel ratio learning value αm in the above equation (2) is an air-fuel ratio learning value calculated based on the air-fuel ratio feedback correction coefficient α. The invalid injection pulse width Ts in equation (2) is an injection pulse width for compensating for a response delay of the fuel injection valve 4 in accordance with the battery voltage.

The air-fuel ratio feedback control is not limited to this case. For example, an O ₂ sensor whose output value changes binaryly with respect to the theoretical air-fuel ratio is provided both upstream and downstream of the catalyst 10, so that the air-fuel ratio of the exhaust falls within the window based on the outputs of these two O ₂ sensors. Alternatively, an air-fuel ratio feedback correction coefficient α [anonymous number] may be calculated.

Even if the air / fuel mixture of the theoretical air / fuel ratio of gasoline is obtained when the engine 2 is new, the flow characteristics of the fuel injection valve 4 and the air flow meter 14 change due to deterioration over time that occurs in the fuel injection valve 4 and the air flow meter 14. In this case, a mixture with the stoichiometric air-fuel ratio of gasoline cannot be obtained. For this reason, the gasoline control unit 11 periodically determines whether or not a failure has occurred in components (hereinafter referred to as “functional system components”) necessary for operating the engine 2 such as the fuel injection valve 4 and the air flow meter 14. Diagnose.

Even if feedback control of the air-fuel ratio is performed as described above, if the sensors 15 and 16 fail or deteriorate, the air-fuel ratio of the exhaust gas cannot be stored in the window, and the harmful three components are efficiently purified. become unable. Similarly, even when the catalyst 10 is deteriorated and the O ₂ storage amount is reduced from the new time, the harmful three components cannot be efficiently purified. For this reason, the gasoline control unit 11 periodically diagnoses whether or not the sensors 15 and 16 are deteriorated and whether or not the catalyst 10 is deteriorated.

Here, a known diagnosis of the sensor 16 during gasoline operation will be briefly described with reference to FIG. FIG. 2 shows a model of how the rotational speed Ne, the fuel injection pulse width Ti1, the O ₂ sensor output, which is the output of the sensor 16, and the like change when the fuel is cut during gasoline operation. When the driver lifts his / her leg from the accelerator pedal, if the rotational speed Ne exceeds the fuel cut rotational speed Nfc, the fuel is rotated at the timing of “t1” when the rotational speed Ne decreases and crosses the fuel cut rotational speed Nfc. Start cutting. Thereafter, for example, when the speed Ne decreases when the driver removes his / her legs from the accelerator pedal and the brake pedal and decreases to the fuel cut recovery rotational speed Nrcv at the timing t2, the fuel cut is canceled and the gasoline is supplied. Resume.

In this case, if the sensor 16 is normal, the O ₂ sensor output decreases with good response from the timing “t1” to zero [V], as indicated by the solid line in the third row of FIG. It rises with good response from the timing of t2 and returns to the value before the fuel cut. On the other hand, when the sensor 16 deteriorates, the responsiveness decreases as indicated by the broken line in the third row of FIG. That is, when the sensor 16 is deteriorated, the O ₂ sensor output becomes zero [V] with a slow response from the timing “t1”, and slowly from the timing “t3” slightly delayed from the timing “t2”. Returns to the value before the fuel cut.

For this reason, the sensor 16 is deteriorated by measuring the time from the fuel cut start timing “t1” until the O ₂ sensor output reaches zero, and comparing the measured time with a predetermined threshold value A1. It can be diagnosed whether or not. For example, when the sensor 16 is new, the time from the fuel cut start timing “t1” until the O ₂ sensor output settles to zero is “Δt1”, and when the sensor 16 deteriorates, the fuel cut start timing “t1” starts from the O ₂ sensor output. Assume that the time until the value settles to zero is “Δt2”. At this time, if the threshold A1 is set between “Δt1” and “Δt2”, it can be diagnosed that the sensor 16 is not deteriorated because “Δt1 <A1” when the sensor 16 is new. Further, when the sensor 16 is deteriorated, “Δt2> A1” is satisfied, and it can be diagnosed that the sensor 16 is deteriorated.

The diagnosis of the sensor 15 during gasoline operation may also be performed by a known diagnosis method. Therefore, the description thereof is omitted here.

Next, a known diagnosis of the catalyst 10 using the outputs of the sensors 15 and 16 during gasoline operation will be briefly described with reference to FIG. FIG. 3 shows how the catalyst upstream air-fuel ratio that is the air-fuel ratio upstream of the catalyst 10, the catalyst downstream O ₂ sensor output that is the output of the sensor 16, and the O ₂ storage amount change when the rotational speed Ne is constant. Is shown as a model.

When the catalyst 10 is not deteriorated, the catalyst downstream O ₂ sensor output changes with a small amplitude as shown by the solid line in the third stage of FIG. When the catalyst 10 deteriorates, the O ₂ storage capacity decreases. Therefore, at this time, the catalyst downstream O ₂ sensor output changes with a large amplitude as indicated by a broken line in the third row of FIG.

When the catalyst 10 is not deteriorated, the O ₂ storage amount changes with a small amplitude as shown by the solid line at the bottom of FIG. As a result, the O ₂ storage amount falls within a predetermined range between the allowable value upper limit H1 and the allowable value lower limit L1 provided around the target value. The target value is 50%, for example. When the catalyst 10 deteriorates, as indicated by a broken line in the lowermost part of FIG. 3, the O ₂ storage amount falls below, for example, the allowable lower limit L1 due to a decrease in the O ₂ storage capacity.

Therefore, when the O ₂ storage amount is within the range between the allowable value upper limit H1 and the allowable value lower limit L1 provided around the target value, it is diagnosed that the catalyst 10 has not deteriorated. it can. Further, when the O ₂ storage amount is out of the range, it can be diagnosed that the catalyst 10 has deteriorated.

In the following, the diagnosis of functional system parts performed during gasoline operation is referred to as “first diagnosis”. Similarly, the diagnosis of the sensors 15 and 16 performed during the gasoline operation and the diagnosis of the catalyst 10 using the outputs of the sensors 15 and 16 are distinguished from the “first diagnosis” as “second diagnosis”.

When the engine 2 includes a variable valve mechanism, a diagnosis performed on the variable valve mechanism is included in the first diagnosis. The gasoline control unit 11 also diagnoses whether a misfire has occurred in the combustion chamber. This misfire diagnosis is also included in the first diagnosis. The diagnosis of the exhaust aftertreatment system performed based on the air-fuel ratio learning value αm is the second diagnosis. The diagnosis of the exhaust aftertreatment system will be described later. In short, the diagnosis of parts and systems related to exhaust aftertreatment is the second diagnosis. Therefore, among the diagnoses performed by the gasoline control unit 11, the remaining diagnoses excluding the second diagnosis are the first diagnoses.

By the way, in countries such as Thailand where not only gasoline but also compressed natural gas (CNG) is commercially available, there is a demand to use both gasoline and CNG fuel as engine fuel. In view of such circumstances, in order to realize the bi-fuel 1, the CNG supply device 31 shown in FIG. 1 can be prepared as an option and added to the engine 2.

The CNG supply device 31 liquefies CNG and supplies it to the engine 2. The CNG supply device 31 mainly includes a CNG cylinder 32, a filling valve 34, a regulator 36, a filter 38, a fuel injection valve 39, a fuel selection switch 41, and a CNG control unit 51.

The CNG cylinder 32 is replenished (filled) with CNG from the filling valve 34 via the high-pressure pipe 33. Natural gas from the CNG cylinder 32 is supplied to the regulator 36 via the high- pressure pipes 33 and 35 and is liquefied by the regulator 36. The cooling water of the engine 2 is used for this natural gas liquefaction. For this reason, the regulator 36 includes two passages 36a and 36b. The regulator 36 exchanges heat by flowing CNG through one passage 36a and cooling water from the engine 2 through the other passage 36b. The regulator 36 cools the CNG by taking heat from the CNG with the cooling water of the engine 2 to produce liquefied natural gas.

The natural gas liquefied by the regulator 36 is supplied to the fuel injection valve 39 for liquefied natural gas through the fuel supply pipe 37 and the filter 38. The configuration of the fuel injection valve 39 is the same as that of the fuel injection valve 4 for gasoline. That is, the fuel injection valve 39 intermittently supplies the liquefied natural gas to the intake passage 3 via the fuel supply pipe 40 in accordance with an instruction from the CNG control unit 51.

The CNG supply device 31 includes cut-off solenoids 42 and 43 in the high- pressure pipes 33 and 35 that stop the supply of CNG in response to a command from the CNG control unit 51 when the CNG operation system fails.

The fuel selection switch 41 is provided in the driver's seat. The fuel selection switch 41 is a switch that is pressed when the driver requests that the engine 2 be operated using CNG as fuel. A signal from the fuel selection switch 41 is input to the CNG control unit 51. A fuel meter is attached to the fuel selection switch 41 to inform the driver of the remaining amount of CNG stored in the CNG cylinder 32.

The CNG control unit 51 receives a signal from the water temperature sensor 44 that measures the temperature of the engine cooling water flowing through the passage 36b and a signal from the intake passage pressure sensor 45 that detects the pressure in the intake passage 3. The CNG control unit 51 operates the engine 2 using CNG as fuel when the coolant temperature reaches the warm-up completion temperature of the engine 2 when the fuel selection switch 41 is pressed.

It is necessary to stop the supply of gasoline when the engine 2 is operated using CNG as fuel (hereinafter referred to as “CNG operation”). For this reason, in the bi-fuel 1, the signal line 21 that communicates from the gasoline control unit 11 to the fuel injection valve 4 for gasoline is configured to pass through the CNG control unit 51. Similarly, the signal line 22 that communicates from the gasoline control unit 11 to the ignition device 5 is configured to go through the CNG control unit 51. For this reason, the signal lines 21 and 22 are divided by the CNG control unit 51. The CNG control unit 51 cuts off the signal lines 21 and 22 during CNG operation, and stops the supply of gasoline and the ignition signal during gasoline operation. Then, the ignition device 5 again outputs an ignition signal during CNG operation from the CNG control unit 51 via the signal line 22.

The combustion method of liquefied natural gas is the same as gasoline and is a compression spark ignition type. For this reason, the fuel injection pulse width and the ignition timing are controlled according to the operating conditions of the engine 2 even during CNG operation. However, the fuel injection pulse width and ignition timing are different from those during gasoline operation. That is, during the CNG operation, the CNG control unit 51 calculates the basic injection pulse width Tp2 [ms] so that an air-fuel mixture having a theoretical air-fuel ratio of liquefied natural gas can be obtained. However, during the CNG operation, the CNG control unit 51 cannot use the signal of the air flow meter 14. Therefore, the CNG control unit 51 uses a signal from the intake passage pressure sensor 45 that detects the pressure in the intake passage 3. That is, the CNG control unit 51 calculates the basic injection pulse width Tp2 [ms] during CNG operation based on the intake passage pressure detected by the intake passage pressure sensor 45.

For example, when the intake passage pressure is close to the atmospheric pressure, the opening degree of the throttle valve 17 is large. The opening of the throttle valve 17 is large on the high load side. When the intake passage pressure is smaller than the atmospheric pressure, the opening degree of the throttle valve 17 is small. The opening of the throttle valve 17 is small on the low load side. That is, the intake passage pressure is a parameter corresponding to the load. For this reason, when the intake passage pressure is close to the atmospheric pressure, the basic injection pulse width Tp2 becomes larger than when the intake passage pressure is smaller than the atmospheric pressure. As a result, the basic injection pulse width Tp2 is larger at the high load side than at the low load side.

In consideration of calculation of the basic injection pulse width Tp2 by applying the basic injection pulse width Tp2 to the basic injection pulse width Tp1 of the above formula (1), the intake passage pressure corresponds to the intake air amount Qa of the above formula (1). . Therefore, the basic injection pulse width Tp2 during CNG operation may be calculated by the following equation.

Tp2 = K2 × intake passage pressure / Ne (3)
Where K2 is a constant,
For example, the engine speed Ne of the expression (3) may be obtained by connecting the two control units 11 and 51 with the CAN 52 and receiving data from the gasoline control unit 11. The CNG control unit 51 calculates the fuel injection pulse width Ti2 [ms] from Tp2 in the equation (3), and opens the natural gas fuel injection valve 39 for a period of the fuel injection pulse width Ti2 at a predetermined fuel injection timing.

Here, the stoichiometric air-fuel ratio of gasoline is 14.9 when the representative molecule of the hydrocarbons constituting gasoline is C ₈ H ₁₈ . The theoretical air-fuel ratio of natural gas is 17.2 when the representative molecule of hydrocarbon is CH ₄ . Therefore, the stoichiometric air-fuel ratio of natural gas is leaner than the stoichiometric air-fuel ratio of gasoline. Therefore, for the same intake air amount, the basic injection pulse width Tp2 during CNG operation may be smaller than the basic injection pulse width Tp1 during gasoline operation.

The fuel injection pulse width Ti2 of the injection performed by the natural gas fuel injection valve 39 at the time of sequential injection is expressed by the following formula.

Ti2 = Tp2 × 2 + Ts (4)
However, Tp2: Basic injection pulse width during CNG operation,
Ts: Invalid injection pulse width [ms],
When the air-fuel ratio of the exhaust gas fluctuates within a predetermined range (window) centering on the theoretical air-fuel ratio of liquefied natural gas as a fuel during CNG operation, the catalyst 10 simultaneously and efficiently detoxifies the harmful three components.

However, during CNG operation, the sensors 15 and 16 output erroneously as described later. If air-fuel ratio feedback control is performed based on erroneous outputs from the sensors 15 and 16, the air-fuel ratio of the exhaust gas may greatly deviate from the stoichiometric air-fuel ratio of liquefied natural gas, and exhaust emission may deteriorate. For this reason, the CNG control unit 51 does not perform air-fuel ratio feedback control during CNG operation in order to avoid deterioration of exhaust emission.

The CNG control unit 51 basically retards the ignition timing during CNG operation than during gasoline operation. This is because knocking tends to occur more easily during CNG operation than during gasoline operation due to the difference in combustion state. Therefore, the CNG control unit 51 retards the ignition timing so that knocking does not occur during the CNG operation because the knocking is more likely to occur than during gasoline operation.

Now, when the inventor performs the diagnosis of each of the sensors 15 and 16, the diagnosis of the catalyst 10 using the outputs of the sensors 15 and 16, and the diagnosis of the exhaust aftertreatment system using the sensor output even during CNG operation, I found for the first time that there was a risk of low diagnosis. When this reason was examined, it became clear that it was as follows.

That is, the sensors 15 and 16 are originally developed for the case where gasoline burns. Specifically, in the sensors 15 and 16, the sensor element unit reacts to a specific gas component generated by gasoline combustion. The outputs of the sensors 15 and 16 are determined depending on the reaction of the sensor element unit. However, the gas components generated by the combustion of liquefied natural gas may be the same as the gas components generated by the combustion of gasoline, or may be different. During CNG operation, it is considered that a gas component different from that during gasoline combustion reacts with the sensor element unit as the specific gas component. As a result, it is considered that the outputs of the sensors 15 and 16 are different from the outputs during gasoline operation.

Here, “the output of the air-fuel ratio sensor is different from the output during gasoline operation” means that the output of the air-fuel ratio sensor is an output equivalent to, for example, the theoretical air-fuel ratio during gasoline combustion, but the liquefied natural gas combustion Sometimes the air-fuel ratio sensor output deviates from the stoichiometric air-fuel ratio and becomes rich or lean output. Also, "O ₂ sensor output becomes an output that is different from the output during the gasoline operation" refers to the output of the O ₂ sensor during gasoline combustion is, for example, a predetermined voltage, the time liquefied natural gas combustion O ₂ It means that the output of the sensor becomes higher than the predetermined voltage or lower than the predetermined voltage.

Note that the outputs of the sensors 15 and 16 return to normal after switching from CNG operation to gasoline operation. For this reason, it is not a failure or deterioration of the sensors 15 and 16 that the sensors 15 and 16 output erroneously only during the CNG operation.

Thus, the sensors 15 and 16 output erroneously during CNG operation. For this reason, if each diagnosis of the sensors 15 and 16 is performed even during CNG operation, or if the diagnosis of the catalyst 10 and the exhaust aftertreatment system using the sensor output is performed, the accuracy of each diagnosis is lowered.

This will be further described with reference to FIG. FIG. 4 shows a CNG operation flag, a second diagnosis permission flag, a second diagnosis flag F1, an air-fuel ratio learning value αm when the engine 2 is started at the timing “t21” when the fuel selection switch 41 is cold. The model shows how the changes. In FIG. 4, the case of the comparative example 1 is indicated by a broken line, and the case of the present embodiment is indicated by a solid line. Comparative Example 1 is a device that is a premise of the present embodiment, and diagnoses the exhaust aftertreatment system using the outputs of the sensors 15 and 16 during CNG operation.

The CNG operation flag is a flag for instructing CNG operation when the CNG operation flag is “1” and gasoline operation when the CNG operation flag is “0”. The second diagnosis permission flag is a flag indicating that the second diagnosis is permitted when the second diagnosis permission flag is “1”, and that the second diagnosis is not permitted when the second diagnosis permission flag is “0”. . The second diagnosis flag F1 is a flag indicating that a failure has occurred in the exhaust aftertreatment system when “1”, and that no failure has occurred in the exhaust aftertreatment system when “0”. Here, it is assumed that the sensors 15 and 16 are developed for gasoline combustion, and that the sensors 15 and 16 are not broken or deteriorated at all. It is assumed that there is no failure or deterioration in the air flow meter 14 and the fuel injection valve 4 which are functional system parts.

In both Comparative Example 1 and this embodiment, the CNG operation flag becomes “0” until the timing of “t23” when the coolant temperature Tw reaches the engine warm-up completion temperature. Until the timing of “t23”, as can be seen from the fact that the CNG operation flag is “0”, gasoline is used as fuel even if the fuel selection switch 41 is pressed. This is because during cold start when combustion is inherently unstable, combustion is more stable when gasoline is used as fuel than when natural gas is used as fuel.

The sensor 15 is activated at a timing “t22” when a predetermined time has elapsed from the start of the engine 2, and air-fuel ratio feedback control is started.

The air-fuel ratio learning value αm as a diagnostic parameter is a value that changes around 1.0. The air-fuel ratio learning value αm is provided with an allowable value upper limit H2 (for example, 1.05) and an allowable value lower limit L2 (for example, 0.95). The allowable value upper limit H2 and the allowable value lower limit L2 define an allowable range of change in the air-fuel ratio learned value αm. Here, no failure or deterioration occurs in each of the parts 15, 16, 14 and 3. For this reason, the air-fuel ratio learned value αm is within a predetermined range between the allowable value upper limit H2 and the allowable value lower limit L2 at the timing of “t22”. As a result, the second diagnosis flag is “0”. That is, it is diagnosed that there is no failure in the exhaust aftertreatment system including the sensors 15 and 16 and the catalyst 10.

From the timing of t23 when the coolant temperature Tw reaches the warm-up completion temperature of the engine 2, the CNG operation flag becomes “1”. Therefore, the CNG control unit 51 performs the CNG operation by switching the fuel from gasoline to CNG from the timing t23.

At this time, in Comparative Example 1, the gasoline control unit 11 continuously calculates the air-fuel ratio learning value αm based on the sensors 15 and 16 even during CNG operation, and the exhaust aftertreatment system is based on the calculated air-fuel ratio learning value αm. Diagnose. In this case, the air-fuel ratio learning value αm calculated based on the outputs of the sensors 15 and 16 gradually becomes smaller than the value at the timing t23. This is due to the following reason.

That is, in this case, the sensors 15 and 16 erroneously output that the air-fuel ratio of the exhaust gas is richer than the stoichiometric air-fuel ratio of gasoline during CNG operation. Therefore, the air-fuel ratio feedback correction coefficient α becomes smaller than 1.0 in order to return the air-fuel ratio of the exhaust to the lean side. As a result of calculating the air-fuel ratio learning value αm based on the feedback correction coefficient α, the air-fuel ratio learning value αm becomes smaller than 1.0. By calculating in this way, the air-fuel ratio learning value αm gradually becomes smaller than the value at the timing of t23.

The period from “t24” to “t25” indicated by “IS” in FIG. 4 and the period from “t26” to “t27” are periods in which the engine 2 is started when the idle stop and the idle stop are released. It is. The start of the engine 2 during this period is performed not by the CNG operation but by the gasoline operation, as can be seen from the fact that the CNG operation flag is “0”. This is because the gasoline operation is more stable in combustion than the CNG operation when the engine 2 is started with the release of the idle stop. During this period, the value of the air-fuel ratio learning value αm immediately before the idling stop permission is held.

In Comparative Example 1, the air-fuel ratio learning value αm falls below the allowable lower limit L2 at the timing “t28” due to an erroneous output of the sensors 15 and 16. As a result, as can be seen from the fact that the second diagnosis flag is “1”, the gasoline control unit 11 erroneously diagnoses that there is a failure in the exhaust aftertreatment system. This is because in Comparative Example 1, the gasoline control unit 11 cannot recognize that CNG is used. For this reason, in Comparative Example 1, the gasoline control unit 11 determines that gasoline is used even during CNG operation. And since the air-fuel ratio learning value αm has decreased across the allowable lower limit L2, it is erroneously diagnosed that there is a failure in the exhaust aftertreatment system.

However, the misdiagnosis occurred because the sensors 15 and 16 output erroneously due to the difference in fuel. In fact, no failure occurred in the exhaust aftertreatment system. Accordingly, it is not appropriate to diagnose whether or not a failure has occurred in the exhaust aftertreatment system when the sensors 15 and 16 output erroneously due to a difference in fuel.

Therefore, in this embodiment, when the CNG operation is in progress, the gasoline control unit 11 stops the second diagnosis, which is the diagnosis of the sensors 15 and 16 and the diagnosis of the catalyst 10 using the outputs of the sensors 15 and 16. That is, the gasoline control unit 11 performs both the first diagnosis and the second diagnosis during gasoline operation, but stops the second diagnosis that is affected by an erroneous sensor output during CNG operation. Therefore, the control units 11 and 51 are configured as follows. That is, as shown in FIG. 1, the control units 11 and 51 are connected by the CAN 52. The CNG control unit 51 transmits a CNG operation to the gasoline control unit 11 via the CAN 52. When the gasoline control unit 11 receives the CNG operation from the CNG control unit 51, the CNG control unit 51 stops the second diagnosis. .

This will be described again with reference to FIG. In the present embodiment, the CNG control unit 51 determines that the CNG operation is being performed during the period from “t23” to “t24”, the period from “t25” to “t26”, and the period after “t27”. It is transmitted to the unit 11 via the CAN 52. In response to this, the gasoline control unit 11 stops calculating the air-fuel ratio learning value αm in the period from “t23” to “t24”, the period from “t25” to “t26”, and the period after “t27”. Then, the value of the air-fuel ratio learning value αm is held at the value immediately before the start of the CNG operation. For this reason, the air-fuel ratio learning value αm does not decrease as in the comparative example 1 in the period after “t23”, as shown by the solid line in the lowermost part of FIG. As a result, as indicated by the solid line in the fifth stage of FIG. 4, in this embodiment, unlike the comparative example 1, the second diagnosis flag F1 remains “0”, and there is a failure in the exhaust aftertreatment system. No misdiagnosis will occur.

Next, the control executed in this embodiment will be described with reference to the flowchart of FIG. The flowchart of FIG. 5 shows a process for setting the CNG operation flag, the first diagnosis permission flag, and the second diagnosis permission flag. The process of the flowchart in FIG. 5 is executed at regular time intervals (for example, every 10 ms). Of the processes shown in the flowchart of FIG. 5, the processes of steps S <b> 1 and S <b> 5 are performed by the CNG control unit 51, and the remaining processes are performed by the gasoline control unit 11.

Note that the CNG operation flag and the second diagnosis permission flag are as described above. The first diagnosis permission flag is a flag indicating that the first diagnosis is permitted when “1”, and that the first diagnosis is not permitted when “0”.

In step S1, it is determined whether or not the engine 2 has been warmed up. This determination is made by comparing the cooling water temperature Tw [° C.] detected by the water temperature sensor 44 with the warm-up completion temperature [° C.]. In step S1, specifically, when the coolant temperature Tw is lower than the warm-up completion temperature, it can be determined that the warm-up of the engine 2 has not yet been completed. Further, when the cooling water temperature Tw becomes equal to or higher than the warm-up completion temperature, it can be determined that the warm-up of the engine 2 has been completed. When the warm-up of the engine 2 is not yet completed, the process proceeds to step S2.

In step S2, the CNG operation flag is set to “0”. When the CNG operation flag is “0”, the gasoline operation is instructed. That is, in the first embodiment, regardless of the fuel selection switch 41, the gasoline operation is first started at the cold start. This is because when the engine 2 is started, combustion is more stable in gasoline operation than in CNG operation.

In step S3, the first diagnosis permission flag is set to “1”. When the first diagnosis permission flag is “1”, diagnosis of the functional system component is executed.

In step S4, the second diagnosis permission flag is set to “1”. When the second diagnosis permission flag is “1”, the diagnosis of the sensors 15 and 16 itself and the diagnosis of the catalyst 10 using the outputs of the sensors 15 and 16 are executed.

When the engine warm-up is completed in step S1, the process proceeds to step S5. In step S5, it is determined whether or not the fuel selection switch 41 is ON. When the fuel selection switch 41 is not pressed, that is, when the fuel selection switch 41 is OFF, the process proceeds to step S2, and the processes of steps S2, S3, and S4 are executed.

When the fuel selection switch 41 is pressed in step S5, that is, when the fuel selection switch 41 is ON, the process proceeds to step S6. In step S6, it is determined whether or not the engine 2 is stopped by determining whether or not the rotational speed Ne [rpm] is zero [rpm]. The rotational speed Ne becomes zero after the warm-up of the engine 2 is completed at the time of idling stop, when the engine is stalled, and when the driver turns off the ignition key. When the rotational speed Ne is not zero, the process proceeds to step S7.

In step S7, the CNG operation flag is set to “1”. When the CNG operation flag = 1, the CNG operation is executed.

In step S8, the first diagnosis permission flag is set to “1”. When the first diagnosis permission flag is “1”, diagnosis of the functional system component is executed.

In step S9, the second diagnosis permission flag is set to “0”. When the second diagnosis permission flag is “0”, the diagnosis of the sensors 15 and 16 and the diagnosis of the catalyst 10 using the outputs of the sensors 15 and 16 are not executed. This is to prevent the accuracy of the second diagnosis from being affected by this effect, because the sensors 15 and 16 output erroneously with the difference in fuel during CNG operation.

When the rotational speed Ne is zero in step S6, the process proceeds to step S10. In step S10, it is determined whether or not the rotational speed Ne was zero last time. When the engine speed Ne is zero this time and was not zero last time, that is, when the engine speed Ne has become zero this time, the process proceeds to step S11. In step S11, the CNG operation flag is set to “0”. This is because when the engine 2 is started after an idle stop or the like, combustion is more stable in gasoline operation than in CNG operation.

When the rotational speed Ne is zero this time and was the previous zero, that is, when the rotational speed Ne is continuously zero, the current processing is terminated as it is.

Next, the function and effect of this embodiment will be described.

The bi-fuel diagnostic device of the present embodiment includes a fuel injection valve 4, a catalyst 10, sensors 15, 16 and a CNG supply device 31. Further, a gasoline control unit 11, a fuel selection switch 41 and a CNG control unit 51 for switching between gasoline operation and CNG operation, diagnosis of the sensors 15 and 16 themselves during gasoline operation, diagnosis of the catalyst 10 using the sensors 15 and 16 outputs, And a gasoline control unit 11 that performs at least one diagnosis of the exhaust aftertreatment system using the outputs of the sensors 15 and 16. The gasoline control unit 11 stops diagnosis performed during gasoline operation during CNG operation.

According to the bifuel diagnostic device of this embodiment, even for the bifuel 1, the diagnosis of the sensors 15 and 16 itself, the diagnosis of the catalyst 10 using the outputs of the sensors 15 and 16, and the outputs of the sensors 15 and 16 are performed. It is possible to prevent a decrease in the reliability of the diagnosis of the exhaust aftertreatment system used.

If the diagnosis of the functional system parts is stopped during CNG operation, the diagnosis result does not remain even if the state of the engine 2 deteriorates during CNG operation. In this regard, in the bifuel diagnostic apparatus of the present embodiment, the gasoline control unit 11 further diagnoses functional system components, that is, components necessary for operating the engine during CNG operation. As a result, the above situation can be avoided.

In the bifuel diagnostic apparatus of the present embodiment, the catalyst 10 is a three-way catalyst, and the sensors 15 and 16 are an air-fuel ratio sensor upstream of the catalyst 10 and an O ₂ sensor downstream of the catalyst 10. The gasoline control unit 11 for diagnosing the exhaust aftertreatment system using the sensor output sets the air / fuel ratio feedback correction coefficient α based on the outputs of the sensors 15 and 16 so that the air / fuel ratio of the exhaust matches the stoichiometric air / fuel ratio. calculate. Such a gasoline control unit 11 calculates the air-fuel ratio learning value αm based on the air-fuel ratio feedback correction coefficient α. Further, such a gasoline control unit 11 diagnoses the exhaust aftertreatment system depending on whether or not the air-fuel ratio learning value αm is between a predetermined allowable value upper limit H2 and a predetermined allowable value lower limit L2. Do.

According to the bi-fuel diagnostic apparatus of the present embodiment, as shown by the solid line in the fifth stage of FIG. 4, the air-fuel ratio learning value αm is received at the lower limit of the allowable value in response to erroneous outputs from the sensors 15 and 16 during CNG operation. It will not fall below L2. As a result, misdiagnosis due to the diagnosis of the exhaust aftertreatment system during CNG operation can be avoided.

(Second Embodiment)
FIG. 6 is a timing chart for explaining diagnosis of the sensor 15 in the second embodiment.

¡The sensor 15 outputs an incorrect output during CNG operation. For this reason, the diagnostic parameter set based on the output of the sensor 15 is affected by this erroneous output. Hereinafter, in the second embodiment, the diagnostic parameter is simply referred to as “diagnostic parameter”. The diagnostic parameter does not indicate an actual value but is merely an image. The timer value T2 is a measurement value of a timer that measures the time after the diagnosis parameter becomes less than the allowable lower limit L3. In the present embodiment, the second diagnostic flag indicates that the sensor 15 has failed or deteriorated when “1”. The CNG operation flag is as described above. The comparative example 2 shows the case where the sensor 15 is diagnosed based on the diagnostic parameter during gasoline operation. In Comparative Example 2, it is assumed that the diagnostic parameter falls between the allowable value upper limit H3 and the allowable value lower limit L3 during gasoline operation. That is, it is assumed that the sensor 15 has not failed or deteriorated.

In this embodiment, the gasoline control unit 11 starts the timer at the timing “t31” when the diagnostic parameter falls below the allowable lower limit L3 during gasoline operation. Then, it is diagnosed that the sensor 15 has failed or deteriorated at the timing when the timer value T2 becomes equal to or greater than the threshold value A2.

In Comparative Example 2, there is a problem when the CNG operation is performed in the middle of diagnosis when the diagnosis parameter changes as shown in the uppermost part of FIG. For example, in FIG. 6, if the timer value T2 continues to increase even when the CNG operation is performed in the period from “t32” to “t34”, the timer value T2 becomes greater than or equal to the threshold A2 at the timing of “t33”. Become. At this time, as is apparent from the fact that the second diagnosis flag F2 is “1”, the sensor 15 is erroneously diagnosed as having failed or deteriorated.

Sensor 15 erroneously outputs during CNG operation as described above. Then, the diagnostic parameter is affected by this erroneous output. As a result, an error occurs in the diagnostic parameter during CNG operation. Therefore, in the comparative example 2 in which the increase of the timer value T2 is continued based on the fact that the diagnostic parameter is less than the allowable lower limit L3 even during the period from “t32” to “t33” in which an error occurs in the diagnostic parameter, The accuracy will be reduced.

Therefore, in the bi-fuel diagnosis apparatus of the second embodiment, when the gasoline control unit 11 switches from gasoline operation to CNG operation at the timing of “t32” during diagnosis and CNG operation is started, the second stage of FIG. As shown by the solid line, the timer value T2 is reset to zero at the timing of “t32”. That is, after “t32”, the diagnosis is temporarily stopped to prevent a decrease in diagnosis accuracy.

The gasoline control unit 11 redoes the diagnosis when the CNG operation is finished and the operation is switched to the gasoline operation. That is, as indicated by the solid line in the second stage of FIG. 6, if the diagnostic parameter is below the allowable lower limit L3 at the timing of “t34” when switching from CNG operation to gasoline operation, the timer value T2 is increased again from zero. Let Then, at the timing of “t35” when the timer value T2 becomes equal to or greater than the threshold value A2, it is diagnosed that the sensor 15 has failed or deteriorated, as can be seen from the fact that the second diagnosis flag F2 is “1”. In the present embodiment, the entire period of redoing is performed during gasoline operation in this manner, so that no error occurs in the diagnostic parameters, and deterioration in diagnostic accuracy is prevented.

Next, the control performed mainly by the gasoline control unit 11 will be described with reference to the flowchart of FIG.

7 shows a process for setting the second diagnosis flag F2 indicating the diagnosis result of the sensor 15. The process of the flowchart of FIG. 7 is performed at regular time intervals (for example, every 10 ms). The process of the flowchart of FIG. 5 is also performed in the second embodiment. The process of the flowchart of FIG. 7 is performed after executing the process of the flowchart of FIG. Note that the flowchart is complicated if both the case where the diagnostic parameter is less than the allowable lower limit L3 and the case where the diagnostic parameter exceeds the allowable upper limit H3 are described. For this reason, description is abbreviate | omitted when a diagnostic parameter exceeds allowable value upper limit H3.

In step S21, it is determined whether or not the second diagnosis flag F2 is “1”. Here, it is assumed that the state before diagnosis, that is, the second diagnosis flag F2 is “0”. At this time, the process proceeds to step S22.

In step S22, it is determined whether or not the second diagnosis permission flag set by executing the processing of the flowchart of FIG. 5 is “1”. When the second diagnosis permission flag is “0”, the current process is terminated.

When the second diagnosis permission flag is “1”, the process proceeds to step S23 in order to diagnose the sensor 15, which is one of the second diagnoses. In step S23, it is determined whether or not the diagnostic parameter is less than the current allowable value lower limit L3. Then, in step S24 following the affirmative determination in step S23, it is determined whether or not the diagnostic parameter was less than the previous allowable value lower limit L3. If the diagnostic parameter is not less than the current allowable lower limit L3 in step S23, the current process is terminated as it is.

If the diagnostic parameter is less than the current allowable lower limit L3 in step S23 and the diagnostic parameter is not less than the previous allowable lower limit L3 in step S24, that is, if the diagnostic parameter is less than the allowable lower limit L3 for the first time this time. The process proceeds to step S25. In step S25, a timer is started. The timer value T2 at the time of activation is “0”.

If the diagnostic parameter is less than the current allowable lower limit L3 in step S23 and the diagnostic parameter is less than the previous allowable lower limit L3 in step S24, that is, if the diagnostic parameter is subsequently less than the allowable lower limit L3, step Proceed to S26. In step S26, it is determined whether or not the CNG operation flag set by executing the processing of the flowchart of FIG. 5 is “1”. When the CNG operation flag is “0”, that is, during gasoline operation, the process proceeds to step S27.

The processing from step S27 to step S29 is a part for diagnosing whether or not the sensor 15 has failed or deteriorated based on the timer value T2. In step S27, the timer value T2 is compared with the threshold value A2. If the timer value T2 is less than the threshold value A2, it is determined that the sensor 15 has not failed or deteriorated. In this case, the process proceeds to step S28. In step S28, the second diagnosis flag F2 is set to “0”.

If the timer value T2 is greater than or equal to the threshold value A2, it is determined in step S27 that the sensor 15 has failed or deteriorated. In this case, the process proceeds to step S29. In step S29, the second diagnosis flag F2 is set to “1”. Since the second diagnosis flag F2 becomes “1” in step S29, the process cannot proceed from step S21 to step S22 after the next time.

When the CNG operation flag is “1” in step S26, that is, during CNG operation, the process proceeds to step S30. In step S30, the timer is reset. That is, the timer value T2 is set to “0”. Subsequently, in step S31, the second diagnosis flag F2 is set to “0”.

The reason for resetting the timer value T2 to zero is as follows. That is, the timer value T2 is increased on condition that the diagnostic parameter is less than the threshold value A2. However, the diagnostic parameter set based on the output of the sensor 15 is affected by the erroneous output of the sensor 15 during CNG operation. For this reason, even during CNG operation, in which the diagnostic parameter is affected by the erroneous output, if the sensor 15 is diagnosed as having failed or deteriorated based on the timer value T2, the diagnostic accuracy is lowered. .

If the diagnostic parameter becomes less than the allowable lower limit L3 after resetting the timer value T2 to zero, the timer is started again in step S25, and the timer value T2 is set to “0”. And if it becomes a gasoline driving | operation, it will progress to step S27 from step S26, and a diagnosis will be performed.

As described above, in the second embodiment, the gasoline control unit 11 that diagnoses the sensor 15 itself starts measuring time when the diagnostic parameter falls below the allowable lower limit L3, and the timer value T2 that is the time measurement value is measured. Is equal to or greater than the threshold value A2, it is diagnosed that the sensor 15 has failed or deteriorated. When the CNG operation is started after the time measurement is started during the gasoline operation, the timer value T2 is reset to zero as can be understood from steps S21 to S24, S26 and S30 shown in FIG. The gasoline control unit 11 starts the time measurement again at the timing when the gasoline operation is performed after the timer value T2 is reset to zero and the diagnosis parameter falls below the allowable lower limit L3. For this reason, even if the bifuel diagnostic apparatus according to the present embodiment is switched during CNG operation during time measurement before diagnosis, it is possible to prevent a decrease in diagnostic accuracy.

(Third embodiment)
FIG. 8 is a timing chart for explaining diagnosis of the sensor 16 in the third embodiment. In addition, the same code | symbol is attached | subjected to the same part as FIG. The O ₂ sensor output is the output of the sensor 16 as described above.

During CNG operation, the sensor 16 outputs an incorrect output. Here, the case where diagnosis of the sensor 16 is performed based on the output of the sensor 16 during gasoline operation is referred to as Comparative Example 3. In Comparative Example 3, it is diagnosed that the sensor 16 has not deteriorated because the period until the O ₂ sensor output becomes zero when the fuel is cut during gasoline operation is less than the threshold value A1.

In the present embodiment, the gasoline control unit 11 diagnoses that the sensor 16 has deteriorated because the period until the O ₂ sensor output becomes zero when the fuel is cut during gasoline operation is equal to or greater than the threshold value A1. The period until the O ₂ sensor output becomes zero at the time of fuel cut is measured by increasing the timer value T1.

In Comparative Example 3, when the O ₂ sensor output changes as indicated by the broken line in the third row in FIG. 8, a problem occurs when the CNG operation is performed during the diagnosis. For example, in FIG. 8, if the timer value T1 continues to increase even when the CNG operation is performed in the period from “t41” to “t43”, the timer value T1 becomes equal to or greater than the threshold value A1 at the timing “t42”. The sensor 16 is erroneously diagnosed as having deteriorated.

The sensor 16 outputs an incorrect output during the CNG operation as described above. For this reason, if the increase in the timer value T1 is continued even during the period from “t41” to “t42” in which an error occurs in the O ₂ sensor output in the comparative example 3, the accuracy of diagnosis is lowered.

Therefore, in the bifuel diagnostic apparatus of the third embodiment, when the gasoline control unit 11 switches from gasoline operation to CNG operation at the timing of “t41” during diagnosis and CNG operation is started, the fourth stage of FIG. As indicated by the one-dot chain line, the timer value T1 is reset to zero at the timing of “t41”. That is, after the timing of “t41”, the diagnosis is temporarily stopped to prevent a decrease in diagnosis accuracy.

The gasoline control unit 11 redoes the diagnosis when the CNG operation ends and the operation is switched to the gasoline operation. Although not shown, the gasoline control unit 11 measures the period until the O ₂ sensor output becomes zero when the fuel is cut by increasing the timer value T1 from zero again when the fuel is cut during gasoline operation. To do. Then, it is diagnosed that the sensor 16 has deteriorated at a timing when the period until the O ₂ sensor output becomes zero at the time of the fuel cut becomes equal to or greater than the threshold value A1. In the present embodiment, the entire period of redoing is performed during gasoline operation in this manner, so that no error occurs in the output of the sensor 16 and the deterioration of diagnostic accuracy is prevented.

Also in the third embodiment, a flowchart corresponding to the flowchart of FIG. 7 described in the second embodiment can be created. However, since the flowchart is the same as the flowchart of FIG. 7, the flowchart is omitted.

In the bi-fuel diagnosis apparatus according to the third embodiment, the gasoline control unit 11 that diagnoses the sensor 16 itself starts measuring time at the timing when fuel cut is started, and the timer value T1 that is the time measurement value is obtained. When the threshold value A1 is exceeded, it is diagnosed that the sensor 16 has deteriorated. Then, the time measurement value is reset to zero when the CNG operation is started after the time measurement is started at the time of fuel cut. Such a gasoline control unit 11 starts the time measurement again at the timing when the gasoline operation is started after the time measurement value is reset to zero and the fuel cut is started. The bifuel diagnostic apparatus according to the present embodiment configured as described above may be switched during CNG operation during time measurement before diagnosis, similarly to the bifuel diagnostic apparatus according to the second embodiment. It is possible to prevent a decrease in diagnostic accuracy.

The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

In the embodiment, the case where the catalyst for purifying the gas after the gasoline burns is a three-way catalyst, but the present invention is not limited to this, and the catalyst may be a NOx trap catalyst.

This application claims priority based on Japanese Patent Application No. 2013-078672 filed with the Japan Patent Office on April 4, 2013, the entire contents of which are hereby incorporated by reference.

Claims (6)

1. A gasoline supply device for supplying gasoline to the engine;
   A catalyst for purifying the gas after the gasoline burns;
   A sensor for operating the catalyst;
   A CNG supply device for liquefying CNG and supplying it to the engine;
   Operation switching means for switching between gasoline operation for operating the engine using the gasoline supply device and CNG operation for operating the engine using the CNG supply device;
   Diagnostic means for performing at least one of diagnosis of the sensor itself, diagnosis of the catalyst using the output of the sensor, and diagnosis of the exhaust aftertreatment system using the output of the sensor during the gasoline operation;
   An operation stop means for stopping the operation of the diagnosis means during the CNG operation;
   A bi-fuel diagnostic device.
2. The bifuel diagnostic device according to claim 1,
   Diagnosing means for diagnosing parts necessary for operating the engine during the CNG operation;
   A bi-fuel diagnostic device further provided.
3. The bi-fuel diagnostic device according to claim 1 or 2,
   The catalyst is a three way catalyst;
   The sensors are an air-fuel ratio sensor upstream of the catalyst and an O ₂ sensor downstream of the catalyst;
   The diagnostic means for diagnosing the exhaust aftertreatment system using the output of the sensor,
   Air-fuel ratio feedback correction coefficient calculating means for calculating an air-fuel ratio feedback correction coefficient so that the air-fuel ratio of the exhaust gas matches the stoichiometric air-fuel ratio based on the outputs of the air-fuel ratio sensor and the O2 sensor;
   Air-fuel ratio learning value calculating means for calculating an air-fuel ratio learning value based on the air-fuel ratio feedback correction coefficient;
   Means for diagnosing the exhaust aftertreatment system depending on whether or not the air-fuel ratio learning value is between a predetermined allowable value upper limit and a predetermined allowable value lower limit;
   A bi-fuel diagnostic device.
4. The bifuel diagnostic device according to any one of claims 1 to 3, wherein
   The diagnostic means for diagnosing the sensor itself starts measuring time when the diagnostic parameter exceeds the upper limit of the allowable value or when the diagnostic parameter falls below the lower limit of the allowable value. And a diagnostic means for diagnosing that the sensor has failed or deteriorated,
   Time measurement value resetting means for resetting the time measurement value to zero when the CNG operation is started after the time measurement is started during the gasoline operation;
   After the time measurement value resetting means resets the time measurement value, the time measurement starts again at the time of gasoline operation and at the timing when the diagnostic parameter exceeds the upper limit of the allowable value or falls below the lower limit of the allowable value. Time measuring means;
   A bi-fuel diagnostic device.
5. The bifuel diagnostic device according to any one of claims 1 to 3, wherein
   The sensor is an O ₂ sensor;
   The diagnostic means for diagnosing the sensor itself starts time measurement at the timing when fuel cut is started, and diagnoses that the O ₂ sensor has deteriorated when the time measurement value is equal to or greater than a threshold value. Diagnostic means,
   Time measurement value resetting means for resetting the time measurement value to zero when the CNG operation is started after the time measurement is started at the time of the fuel cut;
   After the time measurement value resetting means resets the time measurement value, the time measurement means starts the time measurement again at the timing when the gasoline operation is started and the fuel cut is started,
   A bi-fuel diagnostic device.
6. Switching between gasoline operation that operates the engine using a gasoline supply device that supplies gasoline to the engine, and CNG operation that operates the engine using a CNG supply device that liquefies CNG and supplies the engine to the engine,
   During the gasoline operation, diagnosis of the sensor itself for working the catalyst for purifying the gas after combustion of the gasoline, diagnosis of the catalyst using the output of the sensor, and after exhaust using the output of the sensor Perform at least one diagnosis of the processing system,
   The diagnosis performed during the gasoline operation is stopped during the CNG operation.
   Bifuel diagnostic method.

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