JP2012036761A - Fuel state detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel state detecting device for accurately detecting alcohol concentration in fuel independently of changes of alcohol concentration and the temperature.SOLUTION: An engine 10 includes: a fuel temperature sensor 42 for detecting the temperature of fuel; and an electrostatic capacity type alcohol concentration sensor 44 for detecting alcohol concentration in the fuel. An ECU 50 determines a transient state wherein a change amount of the alcohol concentration is a predetermined concentration determination value or more and wherein the change amount of the fuel temperature is a predetermined temperature determination value or more. In the transient state, when the fuel temperature changes in the lowering direction, the ECU 50 corrects a detection value of the alcohol concentration to a low concentration side, and when the fuel temperature changes in the rising direction, the ECU 50 corrects a detection value of the alcohol concentration to a high concentration side. With this structure, a displacement of the concentration detection value different in response to a direction of the temperature change can be accurately corrected, and detection accuracy of the alcohol concentration in the transient state can be improved.

Description

  The present invention relates to a fuel property detection device that is mounted on, for example, an internal combustion engine and is suitably used for detecting the alcohol concentration in fuel.

  As a conventional technique, for example, as disclosed in Patent Document 1 (Japanese Utility Model Publication No. 5-73568), a capacitance-type alcohol concentration detection device applied to an internal combustion engine is known. The alcohol concentration detection device includes a pair of electrodes arranged in the fuel, and detects the alcohol concentration in the fuel based on the capacitance between these electrodes. In the prior art, in consideration of the fact that the capacitance between the electrodes is also affected by the temperature of the fuel, the temperature of the fuel is detected by a temperature sensor, and the detected value of the alcohol concentration is temperature-corrected.

Japanese Utility Model Publication No. 5-73568 JP 2009-145131 A

  By the way, in the prior art described above, a general thermistor or the like is often used as a temperature sensor. However, when comparing the capacitance type concentration sensor and the temperature sensor, there is a large difference in the response characteristics at the time of transition. Therefore, in a transient state where the temperature of the fuel greatly changes with the alcohol concentration in the fuel, a difference occurs between the response speed with respect to the change in alcohol concentration and the response speed with respect to the change in temperature.

  For this reason, in the prior art, for example, when a low-temperature fuel having a significantly different alcohol concentration is supplied to a relatively warm fuel after the vehicle has been warmed up, the alcohol concentration is reduced due to the difference in response characteristics described above. There is a problem that the detection accuracy is lowered. As a result, for example, in the control of an internal combustion engine or the like, the deviation of the air-fuel ratio due to the alcohol concentration detection error increases, and the combustibility and the exhaust emission are likely to deteriorate.

  The present invention has been made to solve the above-described problems. The object of the present invention is to accurately detect the alcohol concentration in the fuel without being affected by changes in the alcohol concentration or temperature. It is an object of the present invention to provide a possible fuel property detection device.

A first invention has at least two electrodes facing each other in a fuel containing alcohol, and a concentration detector that detects an alcohol concentration in the fuel based on a capacitance between the electrodes,
A temperature detector for detecting the temperature of the fuel;
This state is obtained when the change amount of the alcohol concentration detected by the temperature detection unit is greater than or equal to a predetermined concentration determination value and the change amount of the fuel temperature detected by the concentration detection unit is greater than or equal to the predetermined temperature determination value. Transient determination means for determining a transient state;
A first correction unit that corrects the detected value of the alcohol concentration to a low concentration side when the transient determination unit determines that the state is in the transient state and the change in the fuel temperature is in a decreasing direction;
Second correction means for correcting the detected value of the alcohol concentration to a high concentration side when the transient determination means determines that the state is in the transient state and the change in the fuel temperature is in an increasing direction; It is characterized by providing.

According to a second aspect of the present invention, there is provided a frequency-specific detection means for detecting capacitances at the first and second frequencies while switching the frequency of the AC voltage applied to the concentration detection unit to the first and second frequencies. When,
Based on the capacitances detected at the first and second frequencies and the dielectric constants of alcohol and moisture at the first and second frequencies, the alcohol concentration in the fuel is determined according to the moisture content. Moisture correction concentration calculating means for calculating in a corrected state.

  According to a third aspect of the present invention, the alcohol concentration in the fuel and / or the temperature of the fuel are different between the time when the capacitance is detected at the first frequency and the time when the capacitance is detected at the second frequency. And a prohibiting means for prohibiting the operation of the frequency-specific detection means.

4th invention is the determination means which determines whether the condition where the water | moisture content in a fuel could change was produced,
Stop means for stopping the operation of the frequency-specific detection means during a period from when the alcohol concentration in the fuel is calculated by the moisture correction concentration calculation means to when the determination means determines that the situation has occurred, Is provided.

5th invention, the air fuel ratio detection means which detects the air fuel ratio of the exhaust gas which arises when the said fuel burns,
Diagnostic means for diagnosing whether or not the alcohol concentration detection function is normal based on the detected value of the alcohol concentration and the air-fuel ratio of the exhaust gas.

  According to the first invention, in the transient state where the alcohol concentration in the fuel and the fuel temperature change so as to affect the detection accuracy, the alcohol concentration is detected by the first correction means when the change in the fuel temperature is in the decreasing direction. Can be corrected to the low density side. In the transient state, when the change in the fuel temperature is in the increasing direction, the detected value of the alcohol concentration can be corrected to the high concentration side by the second correcting means. As a result, even in a transient state such as during refueling, it is possible to accurately correct the deviation of the concentration detection value that varies depending on the direction of temperature change, and to improve the alcohol concentration detection accuracy.

  According to the second aspect of the invention, the moisture correction concentration calculating means is based on the capacitances detected at the first and second frequencies, respectively, and the dielectric constants of alcohol and moisture at the first and second frequencies. The alcohol concentration in the water-containing fuel can be accurately detected. Therefore, it is possible to accurately detect the alcohol concentration without being affected by moisture in the fuel simply by switching the frequency.

  According to the third aspect of the invention, the prohibiting means differs in alcohol concentration and fuel temperature in the fuel at the time when the capacitance is detected at the first frequency and when the capacitance is detected at the second frequency. In this case, the operation of the frequency-specific detection means can be prohibited. Thereby, it is possible to prevent errors such as capacitance and dielectric constant due to the influence of temperature change and concentration change, and improve the detection accuracy of alcohol concentration.

  According to the fourth invention, the stopping means operates the detecting means for each frequency during a period from when the alcohol concentration in the fuel is once calculated until a situation in which the moisture content in the fuel can change occurs. Can be stopped. Thereby, the frequency unnecessary switching operation can be suppressed, and the number of detectable alcohol concentrations (detection frequency) can be increased.

  According to the fifth aspect of the invention, the diagnosis means accurately diagnoses a failure of the concentration detector or the like only by detecting the exhaust air / fuel ratio by utilizing the correlation between the alcohol concentration in the fuel and the exhaust air / fuel ratio. be able to. Thereby, it is possible to quickly and appropriately cope with the failure, and to improve the reliability of the system.

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole block diagram for demonstrating the system applied to Embodiment 1 of this invention. It is a characteristic diagram which shows the state which an error produces in the detected value of alcohol concentration by the change of fuel temperature. It is a characteristic diagram which shows the output characteristic of an alcohol concentration sensor and temperature sensor in case the temperature of fuel falls. It is a characteristic diagram which shows the output characteristic of an alcohol concentration sensor and a temperature sensor in case the temperature of a fuel rises. In Embodiment 1 of this invention, it is a flowchart of the alcohol concentration detection control performed by ECU. In Embodiment 2 of this invention, it is a characteristic diagram which shows the relationship between the frequency of an applied voltage when a water | moisture content mixes in a fuel, and an electrostatic capacitance. It is a characteristic diagram which shows the frequency characteristic of an electrostatic capacitance about each of a hydrated fuel and a non-hydrated fuel. In Embodiment 2 of this invention, it is a flowchart of the control performed by ECU. In Embodiment 3 of this invention, it is a flowchart of the control performed by ECU.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an overall configuration diagram for explaining a system applied to the first embodiment of the present invention. The system of the present embodiment is mounted on, for example, an FFV (Flexible Fuel Vehicle) and includes an engine 10 as an internal combustion engine using alcohol fuel. Each cylinder of the engine 10 has a combustion chamber 14 defined by a piston 12, and the piston 12 is connected to a crankshaft 16 of the engine. The engine 10 also includes an intake passage 18 that sucks intake air into each cylinder, and an exhaust passage 20 through which exhaust gas is discharged from each cylinder.

  The intake passage 18 is provided with an electronically controlled throttle valve 22 that adjusts the intake air amount based on the accelerator opening and the like. On the other hand, the exhaust passage 20 is provided with a catalyst 24 for purifying the exhaust gas. Each cylinder has an intake port injection valve 26 for injecting fuel into the intake port, an in-cylinder injection valve 28 for injecting fuel into the cylinder, an ignition plug 30 for igniting an air-fuel mixture in the cylinder, and an intake port Is provided with an intake valve 32 for opening and closing the inside of the cylinder, and an exhaust valve 34 for opening and closing the exhaust port with respect to the inside of the cylinder.

  Furthermore, the system of the present embodiment includes a sensor system including a crank angle sensor 36, an air flow sensor 38, an air-fuel ratio sensor 40, a fuel temperature sensor 42, an alcohol concentration sensor 44, and the like, and an ECU ( Electronic Control Unit) 50. First, the sensor system will be described. The crank angle sensor 36 outputs a signal synchronized with the rotation of the crankshaft 16, and the air flow sensor 38 detects the intake air amount. The air-fuel ratio sensor 40 detects the exhaust air-fuel ratio upstream of the catalyst 24, and constitutes the air-fuel ratio detection means of the present embodiment. The fuel temperature sensor 42 detects the temperature of the fuel and constitutes the temperature detection unit of the present embodiment.

  The alcohol concentration sensor 44 detects the alcohol concentration in the fuel, and constitutes the concentration detector of the present embodiment. The alcohol concentration sensor 44 is composed of a capacitance type concentration sensor, and has a known configuration as described in, for example, Japanese Unexamined Patent Application Publication No. 2009-145131. That is, the alcohol concentration sensor 42 includes a pair of electrodes 44A that are opposed to each other in the fuel, and is configured to detect the alcohol concentration in the fuel based on the capacitance between the electrodes 44A.

  In addition to the sensors 36 to 44 described above, the sensor system includes various sensors necessary for controlling the engine 10 and a vehicle on which the engine 10 is mounted (for example, a water temperature sensor for detecting the cooling water temperature of the engine, an accelerator opening degree). And the like, and these sensors are connected to the input side of the ECU 50. Various actuators including the throttle valve 22, the injection valves 26 and 28, the spark plug 30, and the like are connected to the output side of the ECU 50.

  Then, the ECU 50 drives each actuator while detecting operation information of the engine using a sensor system, and executes operation control. Specifically, the engine speed and the crank angle are detected based on the output of the crank angle sensor 36, and the intake air amount is calculated based on the output of the air flow sensor 38. Further, the engine load is calculated based on the intake air amount, the engine speed, and the like, and the fuel injection timing is determined based on the crank angle. Further, the fuel injection amount is calculated based on the intake air amount, the load, the alcohol concentration in the fuel, and the like. When the fuel injection timing comes, the injection valves 26 and 28 are driven, and the spark plug 30 is driven. Thereby, the air-fuel mixture is combusted in the cylinder, and the engine can be operated. Further, the ECU 50 executes air-fuel ratio feedback control for controlling the air-fuel ratio to the target air-fuel ratio based on the output of the air-fuel ratio sensor 40.

[Features of Embodiment 1]
The alcohol concentration in the fuel is calculated by correcting the temperature of the alcohol concentration detected by the alcohol concentration sensor 44 based on the output of the fuel temperature sensor 42. However, in a transient state where the temperature of the fuel greatly changes with the alcohol concentration in the fuel, the detection accuracy of the alcohol concentration is likely to decrease due to the difference in the response characteristics of the sensors 42 and 44. Here, FIG. 2 is a characteristic diagram showing a state where an error occurs in the detected value of the alcohol concentration due to a change in the fuel temperature. As shown in this figure, when the alcohol concentration in the fuel changes, if the temperature of the fuel changes greatly, an error occurs in the detected value of the alcohol concentration compared to the case where there is no temperature change. This phenomenon occurs when, for example, a low temperature fuel with a different alcohol concentration is supplied to the warm fuel after the vehicle is warmed up, or a warm fuel is supplied to the cold fuel immediately after the vehicle is started. Can occur in some cases.

  Further, the detection error has a characteristic that an error generation direction differs depending on a temperature change direction, as shown in FIGS. FIG. 3 is a characteristic diagram showing the output characteristics of the alcohol concentration sensor and the temperature sensor (fuel temperature sensor) when the temperature of the fuel decreases, and FIG. 4 shows the output characteristics when the temperature of the fuel increases. It is a characteristic diagram. First, as shown in FIG. 3, when the actual temperature of the fuel is greatly reduced due to refueling or the like, the temperature detected by the temperature sensor 42 cannot follow the change in the actual temperature, and the detected temperature shifts transiently to the high temperature side. Response delay occurs. On the other hand, since the change in the actual temperature is reflected relatively quickly in the capacitance between the electrodes 44A, the detected concentration by the alcohol concentration sensor 44 shifts to the high temperature side with respect to the actual concentration. On the other hand, as shown in FIG. 4, when the actual temperature of the fuel rises greatly, a response delay occurs in which the detected temperature transiently shifts to the low temperature side, and the detected alcohol concentration falls to the low temperature side with respect to the actual concentration. It will shift.

  For this reason, in the present embodiment, in the transient state where the alcohol concentration in the fuel and the fuel temperature have greatly changed, if the change in the fuel temperature occurs in the decreasing direction, the detected value of the alcohol concentration is reduced (reduced) To compensate for the deviation of the detected value toward the high density side. Also, when the fuel temperature changes in the upward direction in the transient state, the detected value of alcohol concentration is corrected to the higher concentration side (increase direction) to compensate for the deviation of the detected value to the lower concentration side. To do. In these correction processes, the correction amount of the alcohol concentration is set based on parameters such as the detected temperature of the fuel and the rate of change of the detected temperature. The ECU 50 stores in advance a first correction map that is map data created based on the characteristic data shown in FIG. 3 and a second correction map created based on the characteristic data shown in FIG. Yes. Therefore, the ECU 50 can calculate the alcohol concentration correction amount by referring to the first and second correction maps based on the parameters.

  In addition, the correction process is necessary only when the alcohol concentration in the fuel and the fuel temperature change greatly, so that the correction process is executed only in a transient state that occurs during refueling. Here, the transient state is defined, for example, as a state where the amount of change in alcohol concentration is equal to or greater than a predetermined concentration determination value and the amount of change in fuel temperature is equal to or greater than a predetermined temperature determination value. Note that the amount of change in alcohol concentration and fuel temperature is the amount by which the values detected by the sensors 42 and 44 change during a certain period of time, in other words, corresponds to the rate of change per certain period of time. The concentration determination value is set as a minimum value of a concentration change amount (concentration change rate) that affects the alcohol concentration detection accuracy, for example, and the temperature determination value is a temperature that affects the alcohol concentration detection accuracy. It is set as the minimum value of the change amount (temperature change rate). These determination values can be easily obtained by experiments or the like.

  According to the above correction process, even when the alcohol concentration and the fuel temperature in the fuel change greatly in a transitional state such as when refueling, the detected value of the alcohol concentration is increased and decreased according to the direction in which the fuel temperature changes. It can be corrected to the density side. Thereby, the shift | offset | difference of a density | concentration detection value which changes according to the direction of a temperature change can be correct | amended exactly, and the detection accuracy in a transient state can be improved. Therefore, in engine control, it is possible to suppress air-fuel ratio deviation caused by alcohol concentration detection error and to accurately execute air-fuel ratio control and the like.

[Specific Processing for Realizing Embodiment 1]
Next, specific processing for realizing the above-described control will be described with reference to FIG. FIG. 5 is a flowchart of alcohol concentration detection control executed by the ECU in the first embodiment of the present invention. The routine shown in this figure is repeatedly executed at a substantially constant calculation cycle during engine operation. In the routine shown in FIG. 5, first, in step 100, the outputs of the fuel temperature sensor 42 and the alcohol concentration sensor 44 are read, and based on these outputs, the detected value of alcohol concentration (concentration detected value) and the detected value of fuel temperature ( Temperature detection value).

  Next, in step 102, a density change amount that is a difference between the density detection value, that is, the density detection value acquired in the current calculation cycle and the density detection value acquired in the previous calculation cycle is calculated. In step 104, as in the case of the density change amount, a temperature change amount that is a difference between the current temperature detection value and the previous temperature detection value is calculated. Therefore, the amount of change in concentration and the amount of change in temperature are constant amounts of change per time corresponding to the calculation cycle of the routine shown in FIG. Next, in step 106, it is determined whether or not the density change amount is equal to or greater than the above-described density determination value. In step 108, it is determined whether or not the temperature change amount is equal to or greater than the temperature determination value.

  If both the determinations in steps 106 and 108 are established, it is determined that both the alcohol concentration and the temperature are in a transient state, and in step 110, whether or not the temperature change amount is negative. Then, it is determined whether or not the change in the fuel temperature is in a decreasing direction. When this determination is established, in step 112, the correction amount is calculated by referring to the first correction map based on the temperature detection value. Then, using this correction amount, the concentration detection value is temperature-corrected to the low concentration side, and the final alcohol concentration is calculated. If the determination in step 110 is not established, the correction amount is calculated in step 114 with reference to the second correction map based on the temperature detection value. Then, using this correction amount, the concentration detection value is temperature-corrected to the high concentration side, and the final alcohol concentration is calculated. On the other hand, if the determination is unsuccessful at any one of steps 106 and 108, it is determined that there is no transient state in which the detection accuracy decreases, and in step 116, the alcohol concentration detection process in the steady state is executed. That is, in step 116, the concentration detection value is temperature-corrected based on the temperature detection value by a generally known correction process in a steady state, and the final alcohol concentration is calculated.

  In the first embodiment, steps 106 and 108 in FIG. 5 show a specific example of the transient determination means, step 112 shows a specific example of the first correction means, and step 114 shows the second correction means. A specific example is shown.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. The present embodiment is characterized in that, in the configuration of the first embodiment, the detected value of the alcohol concentration is corrected according to the moisture content in the fuel. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 2]
The detected value (capacitance) of the alcohol concentration is affected by components mixed in the fuel, and the degree of influence increases as the relative dielectric constant of the contaminant increases. Here, FIG. 6 is a characteristic diagram showing the relationship between the frequency of the applied voltage and the capacitance when moisture is mixed in the fuel. In the figure, “E100” indicates a fuel having an alcohol concentration of 100%. The relative permittivity of gasoline, alcohol (ethanol), and water is about 2, 24, and 80, respectively, and the relative permittivity of water is particularly large. For this reason, when water is mixed in the fuel, as shown in FIG. 6, the capacitance changes greatly even with a small amount of water, and the alcohol concentration detection accuracy is lowered.

  For this reason, in the present embodiment, the alcohol in the fuel is detected by detecting the capacitance at two different frequencies Fa and Fb by utilizing the fact that the frequency characteristics of the capacitance are different between alcohol and moisture. The concentration is calculated in a state corrected according to the water content. FIG. 7 is a characteristic diagram showing the frequency characteristics of capacitance for each of the hydrous fuel (alcohol fuel containing water) and the non-hydrous fuel. In addition, this characteristic diagram has illustrated the case where ethanol fuel is used as alcohol fuel. As shown in FIG. 7, for example, when the capacitance is detected at a single frequency Fa for a hydrous fuel having an alcohol concentration Ea and a non-hydrous fuel having an alcohol concentration Eb (≠ Ea), the alcohol concentration is Despite being different, the same capacitance C2a may be obtained. That is, it can be seen that an error occurs in the detected value of the alcohol concentration due to the presence of moisture.

  On the other hand, since alcohol and water have different frequency characteristics of capacitance, when a voltage is applied to the above two types of fuels at a different frequency Fb, the capacitance C2b, C1b 'is obtained. Therefore, in any alcohol fuel, if the capacitances C2a and C2b at two types of frequencies Fa and Fb are detected, the water content and alcohol concentration in the fuel can be calculated. Hereinafter, this calculation process will be described in detail.

(Calculation process of alcohol concentration)
First, assuming that the dielectric constants of alcohol at frequencies Fa and Fb are Ka1 and Kb1, respectively, and the dielectric constants of water at frequencies Fa and Fb are Ka2 and Kb2, respectively, capacitances C2a, C2b, and C1b 'shown in FIG. The following formulas (1) to (3) are established. Note that w is the water content (moisture concentration) of the water-containing fuel.

C2a = Ea * Ka1 + w * Ka2 = Eb * Ka1 (1)
C1b '= Eb * Kb1 (2)
C2b = Ea * Kb1 + w * Kb2 (3)

  The middle side of the above formula (1) and the formula (3) are formulas established for the water-containing fuel having the alcohol concentration Ea based on FIG. 7, and the right side of the formula (1) and the formula (2) are the alcohol concentration Eb. This formula holds for non-hydrous fuel. Using these equations, the following equation (4) can be obtained from the right side of (1) and the equation (2), and the following equation (5) can be obtained from the middle and right sides of the equation (1).

C1b '= C2a x (Kb1 / Ka1) (4)
Eb−Ea = w × (Ka2 / Ka1) (5)

  Further, the following expression (6) is obtained by subtracting the expression (3) from the expression (2). By substituting the expressions (4) and (5) into the expression (6), the following (7) ) Formula can be obtained.

C1b'-C2b = (Eb-Ea) * Kb1-w * Kb2 (6)
C2a * (Kb1 / Ka1) -C2b = w * (Ka2 / Ka1) * Kb1-w * Kb2 (7)

  The following equation (8) can be obtained by arranging the equation (7) with respect to the water concentration w. On the other hand, when the left side and the middle side of the formula (1) are arranged for the alcohol concentration Ea as the detection target, the following formula (9) is obtained.

w = (C2a * Kb1-C2b * Ka1) / (Ka2 * Kb1-Ka1 * Kb2) (8)
Ea = (C2a-w * Ka2) / Ka1 (9)

  Therefore, according to the above formulas (8) and (9), based on the capacitances C2a and C2b detected at the two types of frequencies Fa and Fb and the constant dielectric constants Ka1, Kb1, Ka2 and Kb2, The alcohol concentration in the hydrous fuel can be accurately detected. As a result, the alcohol concentration can be accurately detected by only switching the frequency without being affected by moisture in the fuel. Further, since the water concentration w in the fuel can be calculated, the engine or the like can perform appropriate control such as generating a warning or changing the fuel injection amount in accordance with the water content of the fuel. .

  In order to realize the above-described calculation process, the ECU 50 stores map data (dielectric constant map) for obtaining the dielectric constants Ka1, Kb1, Ka2, and Kb2 in advance. More specifically, since the frequency characteristic of the dielectric constant changes according to the alcohol concentration and fuel temperature in the fuel, the dielectric constant map can calculate the dielectric constant based on the latest alcohol concentration and fuel temperature. 2D map data. The ECU 50 can determine the dielectric constants Ka1, Kb1, Ka2, and Kb2 by referring to the dielectric constant map based on the alcohol concentration in the fuel and the fuel temperature.

  In the actual detection operation, the frequency of the alternating voltage applied between the electrodes 44A is alternately switched between the frequencies Fa and Fb, and the capacitances C2a and C2b at the frequencies Fa and Fb are detected. At this time, the voltage application periods at the frequencies Fa and Fb may be different. However, it is preferable to calculate the alcohol concentration using the capacitances C2a and C2b detected in the voltage application periods adjacent to each other in order to make the detection conditions at each frequency as uniform as possible. The alcohol concentration Ea is calculated based on the capacitances C2a and C2b and the dielectric constants Ka1, Kb1, Ka2 and Kb2 obtained from the dielectric constant map, and the water concentration w is also calculated if necessary.

(Detection operation execution conditions)
In the present embodiment, the frequencies Fa and Fb are switched during a period from the time when the alcohol concentration in the fuel is once calculated by the above-described calculation method until the situation in which the moisture content in the fuel may change. The capacitance detection operation is stopped. Here, the situation where the moisture content in the fuel can change is, for example, a case where refueling is performed and the fuel in the fuel tank is replaced with the fuel after refueling. Is a period (property invariant period) during which the fuel property is estimated not to change. For this reason, in this embodiment, it is determined whether or not refueling has been performed and the fuel in the fuel tank has been replaced with fuel after refueling. Only when this determination is satisfied, the two types of frequencies Fa and Fb are used. Detect alcohol concentration.

  On the other hand, when the above determination is not satisfied, that is, when the property is invariant, the switching operation of the frequencies Fa and Fb is stopped. In this case, for example, the final alcohol concentration is calculated by detecting the electrostatic capacitance at a single frequency and performing known temperature correction or the like. According to the above configuration, it is possible to suppress an unnecessary switching operation of the frequency, increase the number of times the alcohol concentration can be detected (detection frequency), and avoid the concentration detection failure. The property invariant period includes situations such as when the vehicle is running (engine is running) or after a certain period of time (transition period) has elapsed since the end of refueling. Therefore, in this embodiment, the switching operation of the frequencies Fa and Fb is stopped when these situations are detected based on, for example, the vehicle speed, the engine speed, the remaining amount of fuel in the fuel tank, and the like. It is good.

  In the present embodiment, the frequencies Fa and Fb are switched when the alcohol concentration in the fuel and / or the fuel temperature differs between the time when the capacitance C2a is detected and the time when the capacitance C2b is detected. All capacitance detection operations are prohibited. More specifically, when detecting the capacitances C2a and C2b, the temperature of the fuel is detected at each detection timing. The above alcohol concentration calculation process (frequency switching) is performed only when the fuel temperature Ta at the time of detecting the capacitance C2a and the fuel temperature Tb at the time of detecting the capacitance C2b are the same. Operation). On the other hand, when the fuel temperatures Ta and Tb are different, the capacitances C2a and C2b are not detected under the same temperature condition, so that there is a possibility that an error occurs in the calculated value of the alcohol concentration. Therefore, in this case, the alcohol concentration calculation process is prohibited.

  In the present embodiment, not only the prohibition condition due to the temperature change described above but also the prohibition condition due to the density change may be added. That is, even when the alcohol concentration at the time of detecting the capacitance C2a is different from the alcohol concentration at the time of detecting the capacitance C2b, the alcohol concentration calculation process is prohibited (the calculated value is determined as the final alcohol concentration). Not used). In addition, in at least one of the capacitances C2a and C2b, a transient error may occur even when the latest detection value is different from the previous detection value, so that the alcohol concentration calculation process is prohibited. It is good also as a structure.

  Furthermore, in the present embodiment, the above-described prohibition condition may be determined without obtaining a change in alcohol concentration or fuel temperature. Specifically, when a situation in which the alcohol concentration or the fuel temperature may change occurs, the capacitance detection operation by switching the frequencies Fa and Fb may be prohibited. Here, the situation in which the alcohol concentration or the fuel temperature can change is, for example, when refueling is performed or when the operating state of the engine changes greatly. For this reason, in the present embodiment, there are two types of frequencies when there is no possibility of refueling (before and after starting the engine) and when the operating state is stable (during execution of fuel cut control). The alcohol concentration is detected by Fa and Fb. In other cases, the alcohol concentration is detected by a single frequency or the alcohol concentration detection is prohibited. If the alcohol concentration is detected after the engine is stopped, the fuel property may change until the next start, so the alcohol concentration detection timing is preferably before the start rather than after the engine is stopped. . According to the above configuration, it is possible to prevent errors such as capacitance and dielectric constant due to the influence of temperature change and concentration change, and improve the detection accuracy of alcohol concentration.

  The alcohol concentration calculation process described above is executed in combination with the concentration detection control described in the first embodiment. That is, in the present embodiment, when it is determined that the alcohol concentration in the fuel and the fuel temperature are in a transient state, the concentration detection control described in the first embodiment is executed, and in other cases, In the steady state, the alcohol concentration calculation process described in the second embodiment is executed.

[Specific Processing for Realizing Embodiment 2]
Next, specific processing for realizing the above-described control will be described with reference to FIG. FIG. 8 is a flowchart of control executed by the ECU in the second embodiment of the present invention. The routine shown in this figure is performed in step 116 of the first embodiment (FIG. 5). In the routine shown in FIG. 8, first, in step 200, it is determined whether the fuel temperature sensor 42, the alcohol concentration sensor 44, etc. are activated, and in step 202, it is determined whether the fuel deterioration determination is completed. . If each sensor is activated and the deterioration determination is not completed, it is determined in step 204 whether or not refueling has been executed. This determination is performed, for example, by detecting the remaining amount of fuel stored in the fuel tank or by detecting the opening / closing operation of the fuel filler opening.

  If the determination in step 204 is not established, refueling has not been performed, and in step 206, the capacitance C2a is read while applying a voltage at the frequency Fa. Further, the fuel temperature Ta at the frequency Fa is read. Next, in step 208, the capacitance C2b is read while applying a voltage at the frequency Fb. Further, the fuel temperature Tb at the frequency Fb is read. In step 210, it is determined whether or not the absolute value | Tb−Ta | of the difference between the fuel temperatures Ta and Tb is smaller than a predetermined allowable limit Ts. Here, the allowable limit Ts is for allowing variation in temperature detection, and is set according to the detection resolution of the fuel temperature sensor 42 and the like.

  If the determination in step 210 is established, it can be considered that the fuel temperatures Ta and Tb coincide with each other. Therefore, in step 212, the alcohol concentration is calculated based on the capacitances C2a and C2b as described above. If the determination in step 210 is not established, the temperature has changed while the electrostatic capacitances C2a and C2b are being detected. Therefore, the switching operation of the frequencies Fa and Fb is stopped, and the control is ended as it is. Thereby, alcohol concentration is detected using a single frequency, for example.

  On the other hand, if the determination in step 204 is established, refueling has been executed. First, in step 214, for example, it is necessary to replace the fuel in the fuel tank based on the remaining fuel amount before and after refueling. Calculate the required fuel consumption Q1. In step 216, an integrated fuel consumption amount Q, which is an integrated value of the amount of fuel consumed so far, is calculated. In step 218, it is determined whether the integrated fuel consumption amount Q has exceeded the required fuel consumption amount Q1. . If this determination is established, it is determined that the fuel in the fuel tank has been replaced with the fuel after refueling, and the routine proceeds to step 206. On the other hand, if the determination in step 218 is not established, the fuel has been supplied, but the fuel in the tank has not been replaced yet, so the control is terminated as it is. That is, in this case, the switching operation of the frequencies Fa and Fb is stopped, and the alcohol concentration is detected by a single frequency, for example.

  In the embodiment, steps 206 and 208 in FIG. 8 show a specific example of the frequency-specific detection means in claim 2, and step 212 shows a specific example of the moisture correction concentration calculation means. Step 210 shows a specific example of prohibiting means in claim 3, and steps 204 and 214 to 218 show specific examples of stopping means in claim 4.

Embodiment 3 FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. The present embodiment is characterized in that the operating state of the alcohol concentration sensor is diagnosed based on the output of the air-fuel ratio sensor in the first embodiment or the second embodiment. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 3]
The alcohol concentration in the fuel detected by the first and second embodiments is used for fuel injection control. In the fuel injection control, for example, the fuel injection amount is determined by a known method based on parameters such as the intake air amount, the engine speed, the engine warm-up state, and the alcohol concentration in the fuel. Since the combustion state in the cylinder changes according to the fuel injection amount, there is a certain correlation between the alcohol concentration in the fuel and the air-fuel ratio of the exhaust gas. For this reason, when an error occurs in the concentration detection value due to a failure of the alcohol concentration sensor 44 or the like, the relationship between the alcohol concentration and the air-fuel ratio deviates from the predetermined correlation.

  In the present embodiment, the above principle is used to diagnose whether the alcohol concentration sensor 44 is normal based on the detected alcohol concentration value and the air-fuel ratio. More specifically, the ECU 50 stores in advance map data for calculating an appropriate air-fuel ratio based on the alcohol concentration. This map data can be obtained, for example, by measuring the relationship between the alcohol concentration and the air-fuel ratio by experiments or the like while maintaining parameters other than the alcohol concentration in a certain reference state.

  During the operation of the engine, first, the map data is referred to based on the detected value of the alcohol concentration, and an appropriate air-fuel ratio to be obtained at the alcohol concentration is calculated. This calculation process is executed when the other parameter is in the reference state (or in a state in which the other parameter is controlled to the reference state). Next, the actual air-fuel ratio detected by the air-fuel ratio sensor 40 is compared with an appropriate air-fuel ratio, and if the difference between the two is larger than the normal variation range, an abnormality such as a failure occurs in the alcohol concentration sensor 44. Diagnose it. This diagnostic process is executed in a state where it is confirmed that the air-fuel ratio sensor 40 is normal by a known diagnostic control or the like. Further, as described in the second embodiment, when a transitional change occurs in the alcohol concentration or fuel temperature in the fuel, an error is likely to occur in the detected value of the alcohol concentration. To do.

  According to the above control, the failure of the alcohol concentration sensor 44 can be accurately diagnosed only by using the output of the air-fuel ratio sensor 40. Thereby, it is possible to quickly and appropriately cope with the failure of the sensor, and to improve the reliability of the system. In the above description, the diagnosis is performed when the other parameters are in the reference state. However, the present invention is not limited to this, and the relationship between each parameter including the alcohol concentration and the air-fuel ratio may be configured as data as multidimensional map data. Thereby, in an arbitrary operation state, an appropriate air-fuel ratio can be calculated based on each parameter, and failure diagnosis of the alcohol concentration sensor 44 can be executed.

[Specific Processing for Realizing Embodiment 3]
Next, specific processing for realizing the above-described control will be described with reference to FIG. FIG. 9 is a flowchart of control executed by the ECU in the third embodiment of the present invention. The routine shown in this figure is executed in parallel with the routine of the first embodiment (FIG. 5) or the routine of the second embodiment (FIGS. 5 and 8). In the routine shown in FIG. 9, first, in step 300, the outputs of the air-fuel ratio sensor 40 and the alcohol concentration sensor 44 are read, and based on these detection values, the detected value of alcohol concentration (concentration detection value) and the actual air-fuel ratio are obtained. Get each. Next, in step 302, an appropriate air-fuel ratio obtained when the sensor is normal is calculated by referring to the map data based on the concentration detection value (and other parameters).

  In step 304, the difference between the actual air-fuel ratio and the appropriate air-fuel ratio is calculated, and it is determined whether this difference is greater than the failure determination value. Here, the failure determination value is set based on, for example, a normal variation range of the air-fuel ratio. If the determination in step 304 is established, it is diagnosed in step 306 that the alcohol concentration sensor 44 has failed. If the determination in step 304 is not established, it is determined in step 308 that the alcohol concentration sensor 44 is normal. In the above description, steps 304 to 308 shown in FIG. 9 show a specific example of the diagnostic means in claim 5.

  In each of the above embodiments, the fuel temperature sensor 42 and the alcohol concentration sensor 44 are configured by separate sensor parts, and the output signal processing of each sensor is executed by the ECU 50. However, the present invention is not limited to this. For example, the concentration detection unit and the temperature detection unit, and a signal processing unit that performs the output signal processing in the same manner as the ECU 50 are integrated or mounted on a substrate. The system may be realized.

  Further, in the embodiment, the case where the fuel property detection device is applied to the internal combustion engine (engine 10) is exemplified. However, the present invention is not limited to an internal combustion engine, but can be widely applied to various industrial machines and combustion devices using alcohol fuel.

10 Engine (Internal combustion engine)
12 piston 14 combustion chamber 16 crankshaft 18 intake passage 20 exhaust passage 22 throttle valve 24 catalyst 26, 28 injection valve 30 spark plug 32 intake valve 34 exhaust valve 36 crank angle sensor 38 air flow sensor 40 air-fuel ratio sensor (air-fuel ratio detection means)
42 Fuel temperature sensor (temperature detector)
44 Alcohol concentration sensor (concentration detector)
50 ECU

Claims (5)

A concentration detector that has at least two electrodes facing each other in a fuel containing alcohol, and that detects an alcohol concentration in the fuel based on a capacitance between the electrodes;
A temperature detector for detecting the temperature of the fuel;
This state is obtained when the change amount of the alcohol concentration detected by the temperature detection unit is greater than or equal to a predetermined concentration determination value and the change amount of the fuel temperature detected by the concentration detection unit is greater than or equal to the predetermined temperature determination value. Transient determination means for determining a transient state;
A first correction unit that corrects the detected value of the alcohol concentration to a low concentration side when the transient determination unit determines that the state is in the transient state and the change in the fuel temperature is in a decreasing direction;
A second correction unit that corrects the detected value of the alcohol concentration to a higher concentration side when the transient determination unit determines that the state is in the transient state and the change in the fuel temperature is in an increasing direction;
A fuel property detection device comprising: A frequency-specific detection means for detecting capacitances at the first and second frequencies while switching the frequency of the AC voltage applied to the concentration detection unit to the first and second frequencies,
Based on the capacitances detected at the first and second frequencies and the dielectric constants of alcohol and moisture at the first and second frequencies, the alcohol concentration in the fuel is determined according to the moisture content. Moisture correction concentration calculating means for calculating in a corrected state;
The fuel property detecting device according to claim 1, comprising:   Detection by frequency when the alcohol concentration in the fuel and / or the temperature of the fuel are different between the time when the capacitance is detected by the first frequency and the time when the capacitance is detected by the second frequency. 3. The fuel property detecting device according to claim 2, further comprising prohibiting means for prohibiting the operation of the means. Determination means for determining whether or not a situation has occurred in which the moisture content in the fuel may change;
Stop means for stopping the operation of the frequency-specific detection means during a period from when the alcohol concentration in the fuel is calculated by the moisture correction concentration calculation means to when the determination means determines that the situation has occurred,
The fuel property detecting device according to claim 2 or 3, comprising: Air-fuel ratio detecting means for detecting an air-fuel ratio of exhaust gas generated by the combustion of the fuel;
Diagnosing means for diagnosing whether the alcohol concentration detection function is normal based on the detected value of the alcohol concentration and the air-fuel ratio of the exhaust gas;
The fuel property detection device according to any one of claims 1 to 4, further comprising:

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