JP2010275910A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect generation of vapor, when the vapor is generated in fuel. <P>SOLUTION: This control device for an internal combustion engine includes an electrostatic capacitance alcohol concentration sensor 41 detecting an alcohol concentration in fuel supplied to the engine 11; and a fuel temperature sensor 42 detecting fuel temperature. In the electrostatic capacitance alcohol concentration sensor 41, attention is paid to the fact that the output of the sensor is fluctuated when vapor generated in fuel passes between electrodes; and when it is determined that the fuel temperature is in a higher temperature region than a predetermined temperature and it is determined that the output fluctuation of the alcohol concentration sensor 41 is a predetermined value or more, it is determined that there is generation of vapor in fuel, and the amount of fuel injected is corrected in an amount increasing direction by a predetermined amount. Meanwhile, when it is determined that the fuel temperature is not in the higher temperature region than the predetermined temperature (the fuel temperature is in a lower temperature region than the predetermined temperature) or it is determined that the output fluctuation of the alcohol concentration sensor 41 is smaller than the predetermined value, it is determined that there is no generation of vapor within fuel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine that can be operated with a plurality of types of fuel having different fuel properties.

In recent years, demands for automobiles equipped with engines (internal combustion engines) that can use gasoline, alcohol, and mixed fuels of both as fuels have increased due to social demands such as reducing CO ₂ emissions and using alternative fuels for oil. is doing. In such an automobile, when fuel with a different alcohol concentration from the previous time is supplied to the fuel tank, the alcohol concentration of the fuel in the fuel tank changes. Since the stoichiometric air-fuel ratio differs between gasoline and alcohol, if the alcohol concentration of the fuel changes, the stoichiometric air-fuel ratio of the fuel also changes. Therefore, it is necessary to change the fuel injection amount (actual air-fuel ratio) according to the alcohol concentration of the fuel. There is.

  Therefore, there is an apparatus in which the alcohol concentration of the fuel supplied to the internal combustion engine is detected by an alcohol concentration sensor, and the fuel injection amount is corrected according to the detected alcohol concentration value. As the alcohol concentration sensor, a capacitance type alcohol concentration sensor and an optical alcohol concentration sensor are known.

  As described in Patent Document 1 (Japanese Patent Application Laid-Open No. 6-222032), the capacitance type alcohol concentration sensor changes the relative permittivity of the fuel in accordance with the alcohol concentration of the fuel and passes the fuel. The alcohol concentration is detected by measuring the capacitance between the electrodes by utilizing the change in the capacitance between the electrodes.

Japanese Patent Laid-Open No. 6-222032

  By the way, as shown in FIG. 3, alcohol fuel (100% alcohol or mixed fuel containing alcohol) tends to have a higher vapor pressure and lower boiling point than gasoline. In addition, vapor (bubbles) easily occurs in the fuel. For this reason, even if the fuel injection amount is corrected in accordance with the alcohol concentration detection value detected by the alcohol concentration sensor, there is a possibility that the control accuracy of the fuel injection amount is lowered if vapor is generated in the fuel. In order to deal with such a malfunction due to the occurrence of vapor, it is necessary to detect the occurrence of vapor in the fuel. However, in the conventional technology, even if vapor occurs in the fuel, it is accurately detected. It cannot be detected.

  Accordingly, an object of the present invention is to provide a control device for an internal combustion engine that can accurately detect the occurrence of vapor in fuel.

  In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an internal combustion engine control apparatus that can be operated with a plurality of types of fuel having different fuel properties, and an electrostatic capacitance between electrodes through which fuel supplied to the internal combustion engine passes. A capacitance type alcohol concentration sensor that detects the alcohol concentration of the fuel by measuring the capacity, and a vapor determination means that determines the state of vapor generation in the fuel based on the behavior of the output of the alcohol concentration sensor. This is a configuration.

  Originally, the alcohol concentration sensor should not change so much except when the fuel concentration in the fuel tank is changed and the alcohol concentration of the fuel changes, but the relative permittivity of the fuel (for example, 2 to 30) and the fuel Since the relative permittivity (for example, 1) of the vapor generated in the inside differs greatly, as shown in FIG. 4, the capacitance type alcohol concentration sensor is used when the vapor generated in the fuel passes between the electrodes. The capacitance between the electrodes varies, and the sensor output varies accordingly. By paying attention to such a phenomenon and monitoring the behavior of the output of the capacitance type alcohol concentration sensor, it is possible to accurately determine the state of occurrence of vapor in the fuel (for example, whether or not vapor has occurred) When vapor is generated in the fuel, it can be accurately detected.

  In general, no vapor is generated when the fuel temperature is low (when the vapor pressure of the fuel is low), and vapor is generated when the fuel temperature is high (when the vapor pressure of the fuel is high). Further, when vapor is generated, the output of the alcohol concentration sensor fluctuates relatively greatly. Accordingly, the fuel temperature determination means for determining the temperature of the fuel is provided as in claim 2, and the vapor determination means is in a high temperature region where the fuel temperature determined by the fuel temperature determination means is equal to or higher than a predetermined temperature and the output of the alcohol concentration sensor. It may be determined that vapor has occurred in the fuel when the fluctuation is equal to or greater than a predetermined value. In this way, when the output of the alcohol concentration sensor fluctuates relatively small due to the fuel temperature being lower than the predetermined temperature and no vapor is generated or for some reason (for example, battery voltage fluctuation, etc.) It is possible to prevent erroneous determination that vapor has occurred, and to improve the detection accuracy of vapor generation.

  Further, when vapor is generated in the fuel, even if the injection time of the fuel injection valve is the same, the actual injection amount may decrease, and the control accuracy of the fuel injection amount may be reduced. As a countermeasure against this, as in claim 3, it may be configured to include a correction means for correcting the fuel injection amount to be increased when it is determined by the vapor determination means that vapor has occurred in the fuel. In this way, it is possible to prevent a decrease in control accuracy of the fuel injection amount due to the generation of vapor.

FIG. 1 is a diagram showing a schematic configuration of an engine control system in one embodiment of the present invention. FIG. 2 is a characteristic diagram showing the relationship between the fuel temperature and the relative dielectric constant of the fuel. FIG. 3 is a characteristic diagram showing the relationship between the fuel temperature and the saturated vapor pressure of the fuel. FIG. 4 is a time chart showing the behavior of the sensor output when vapor is generated. FIG. 5 is a flowchart showing the flow of processing of the vapor determination routine.

Hereinafter, an embodiment embodying a mode for carrying out the present invention will be described.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. A throttle valve 16 whose opening is adjusted by a motor 15 and a throttle opening sensor 17 for detecting the opening (throttle opening) of the throttle valve 16 are provided on the downstream side of the air flow meter 14.

  Further, a surge tank 18 is provided on the downstream side of the throttle valve 16, and an intake pipe pressure sensor 19 for detecting the intake pipe pressure is provided in the surge tank 18. The surge tank 18 is provided with an intake manifold 20 that introduces air into each cylinder of the engine 11, and a fuel injection valve that injects fuel toward the intake port in the vicinity of the intake port of the intake manifold 20 of each cylinder. 21 is attached. An ignition plug 22 is attached to the cylinder head of the engine 11 for each cylinder, and the air-fuel mixture in the cylinder is ignited by spark discharge of the ignition plug 22 of each cylinder.

  On the other hand, the exhaust pipe 23 of the engine 11 is provided with an exhaust gas sensor 24 (air-fuel ratio sensor, oxygen sensor, etc.) for detecting the air-fuel ratio or rich / lean of the exhaust gas. A catalyst 25 such as a three-way catalyst for purifying gas is provided.

  A cooling water temperature sensor 26 that detects the cooling water temperature and a knock sensor 29 that detects knocking are attached to the cylinder block of the engine 11. A crank angle sensor 28 that outputs a pulse signal every time the crankshaft 27 rotates by a predetermined crank angle is attached to the outer peripheral side of the crankshaft 27. Based on the output signal of the crank angle sensor 28, the crank angle and engine The rotation speed is detected.

  The engine 11 can use any of a plurality of types of fuel having different fuel properties, for example, gasoline, alcohol such as ethanol or methanol, and alcohol mixed fuel obtained by mixing alcohol with gasoline. In addition, any one of alcohol and alcohol mixed fuel is selected and refueled in the fuel tank 30. A fuel pump 31 that pumps up fuel is provided in the fuel tank 30. The fuel discharged from the fuel pump 31 is sent to the delivery pipe 33 through the fuel pipe 32 and is distributed from the delivery pipe 33 to the fuel injection valve 21 of each cylinder. A fuel filter 34 and a pressure regulator 35 are connected in the vicinity of the fuel pump 31 in the fuel pipe 32, and the discharge pressure of the fuel pump 31 is regulated to a predetermined pressure by the pressure regulator 35, and surplus fuel exceeding that pressure The minute amount is returned into the fuel tank 30 by the fuel return pipe 36.

  An alcohol concentration sensor 41 that detects the alcohol concentration of the fuel supplied to the engine 11 is attached to a predetermined position of the fuel passage (fuel pipe 32 or delivery pipe 33) from the fuel tank 30 to the fuel injection valve 21. Yes. The alcohol concentration sensor 41 is a capacitance-type alcohol concentration sensor, and the relative permittivity of the fuel changes according to the alcohol concentration of the fuel, and the capacitance between the electrodes through which the fuel passes changes. The alcohol concentration is detected by measuring the capacitance between the electrodes. The location where the alcohol concentration sensor 41 is attached is not limited to the fuel passage, and may be inside the fuel tank 30. Further, the alcohol concentration sensor 41 is integrally provided with a fuel temperature sensor 42 (fuel temperature determination means) for detecting the temperature of the fuel. The fuel temperature sensor 42 may be provided separately from the fuel property sensor 41.

  A canister 38 is connected to the fuel tank 30 via an evaporation pipe 37. The canister 38 accommodates an adsorbent (not shown) such as activated carbon that adsorbs the evaporation gas (evaporated fuel gas). Between the canister 38 and the engine intake system (for example, the intake pipe 12 or the surge tank 18 or the intake manifold 20 on the downstream side of the throttle valve 16), the evaporated gas adsorbed by the adsorbent in the canister 38 is purged to the engine intake system. A purge passage 39 for (release) is provided, and a purge control valve 40 for adjusting the purge flow rate according to the engine operating state is provided in the middle of the purge passage 39.

  Outputs of the various sensors described above are input to a control circuit (hereinafter referred to as “ECU”) 43. The ECU 43 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium), so that the fuel injection amount of the fuel injection valve 21 can be changed according to the engine operating state. The ignition timing of the spark plug 22 is controlled.

  At this time, the ECU 43 matches the air-fuel ratio of the exhaust gas to the target air-fuel ratio (for example, the theoretical air-fuel ratio) based on the output of the exhaust gas sensor 24 when a predetermined air-fuel ratio feedback control execution condition is satisfied during engine operation. Thus, the air-fuel ratio feedback correction amount is calculated, and the air-fuel ratio feedback control for correcting the fuel injection amount of the fuel injection valve 21 using this air-fuel ratio feedback correction amount is executed.

  In addition, the higher the alcohol concentration (for example, ethanol concentration) of the fuel, the lower the theoretical air-fuel ratio of the fuel, and the higher the fuel injection amount necessary for controlling the actual air-fuel ratio to the theoretical air-fuel ratio. Considering this, the ECU 43 corrects the fuel injection amount of the fuel injection valve 21 in accordance with the alcohol concentration detection value of the fuel detected by the alcohol concentration sensor 41.

  Here, the capacitance-type alcohol concentration sensor 41 detects the alcohol concentration by measuring the capacitance between the electrodes through which the fuel passes. However, as shown in FIG. 2, even if the alcohol concentration of the fuel is the same, the relative dielectric constant of the fuel changes depending on the fuel temperature and the capacitance between the electrodes changes. Therefore, the alcohol concentration sensor 41 is affected by the influence of the fuel temperature. Output (alcohol concentration detection value) changes. As a countermeasure, the ECU 43 corrects the output (alcohol concentration detection value) of the alcohol concentration sensor 41 according to the fuel temperature detected by the fuel temperature sensor 42.

  By the way, as shown in FIG. 3, alcohol fuel (100% alcohol or mixed fuel containing alcohol) tends to have a higher vapor pressure and lower boiling point than gasoline. In addition, vapor (bubbles) easily occurs in the fuel. For this reason, even if the fuel injection amount is corrected according to the alcohol concentration detection value detected by the fuel property sensor 41, the control accuracy of the fuel injection amount may be reduced if vapor is generated in the fuel. In order to cope with such a malfunction due to the occurrence of vapor, it is necessary to detect the occurrence of vapor in the fuel.

  Therefore, in this embodiment, the ECU 43 executes a vapor determination routine of FIG. 5 described later, thereby determining the state of vapor generation in the fuel based on the behavior of the output of the alcohol concentration sensor 41. Since the relative dielectric constant of the fuel (for example, 2 to 30) and the relative dielectric constant of the vapor generated in the fuel (for example, 1) are greatly different, as shown in FIG. When the vapor generated in the fuel passes between the electrodes, the capacitance between the electrodes varies, and the sensor output varies accordingly. By paying attention to such a phenomenon and monitoring the behavior of the output of the capacitance-type alcohol concentration sensor 41, it is possible to accurately determine the state of vapor generation in the fuel (for example, whether vapor has been generated). .

Hereinafter, the processing content of the vapor determination routine of FIG. 5 executed by the ECU 43 will be described.
The vapor determination routine shown in FIG. 5 is repeatedly executed at a predetermined cycle while the ECU 43 is powered on, and serves as a vapor determination means in the claims. When this routine is started, first, in step 101, the fuel temperature detected by the fuel temperature sensor 42 is read, and then the process proceeds to step 102, where it is determined whether or not the fuel temperature is in a high temperature region equal to or higher than a predetermined temperature. . Here, the predetermined temperature is a lower limit value of the fuel temperature at which vapor can be generated or a fuel temperature slightly lower than that, and the predetermined temperature may be calculated by a map or the like according to the alcohol concentration of the fuel, Alternatively, the predetermined temperature may be a preset fixed value (for example, a lower limit value of a fuel temperature at which vapor can be generated in gasoline or a fuel temperature slightly lower than that).

  If it is determined in step 102 that the fuel temperature is in a high temperature region equal to or higher than the predetermined temperature, it is determined that vapor may be generated, and the process proceeds to step 103 where the output of the alcohol concentration sensor 41 is read. . At this time, the sensor output after removing the noise component (high-frequency component) included in the output of the alcohol concentration sensor 41 by performing a low-pass filter process that passes only the low-frequency component of the output of the alcohol concentration sensor 41. May be read.

  Thereafter, the process proceeds to step 104, where it is determined whether or not the output fluctuation of the alcohol concentration sensor 41 is equal to or greater than a predetermined value. Specifically, it is determined whether or not the amplitude of the output fluctuation of the alcohol concentration sensor 41 (for example, the difference between the peak value and the bottom value of the output) is greater than or equal to a predetermined value. Alternatively, when vapor is generated in the fuel, the output of the alcohol concentration sensor 41 fluctuates more slowly than noise, so the output fluctuation time of the alcohol concentration sensor 41 (for example, the output exceeds the peak value from the bottom value). It is determined whether or not the time required for returning to the bottom value again, the time required for the output to change from the bottom value to the peak value, the time required for the output to fluctuate by a predetermined amount, etc. Anyway. Further, it may be determined whether the output fluctuation amplitude of the alcohol concentration sensor 41 is equal to or greater than a predetermined value and whether the output fluctuation time is equal to or greater than a predetermined value.

  If it is determined in step 104 that the output fluctuation of the alcohol concentration sensor 41 is greater than or equal to a predetermined value, the process proceeds to step 105, where it is determined that vapor in the fuel is generated. At this time, when it is determined only once that the output fluctuation of the alcohol concentration sensor 41 is equal to or greater than a predetermined value, it may be determined that vapor has occurred in the fuel, or within a predetermined period. You may make it determine with the generation | occurrence | production of the vapor | steam in fuel, when the frequency | count that it was determined that the output fluctuation | variation of the alcohol concentration sensor 41 is more than a predetermined value reaches a predetermined frequency.

  Thereafter, the routine proceeds to step 106, where the fuel injection amount (for example, at least one of the requested fuel injection amount, the injection time, the air-fuel ratio feedback correction amount, etc.) is corrected in the increasing direction by a predetermined amount. The processing in step 106 serves as correction means in the claims.

  On the other hand, if it is determined in step 102 that the fuel temperature is not in the high temperature region above the predetermined temperature (the fuel temperature is a low temperature region lower than the predetermined temperature), or the output fluctuation of the alcohol concentration sensor 41 is determined in step 104. Is determined to be smaller than the predetermined value, the routine proceeds to step 107, where it is determined that no vapor is generated in the fuel.

  In the present embodiment described above, the capacitance-type alcohol concentration sensor 41 focuses on the fact that the sensor output fluctuates when the vapor generated in the fuel passes between the electrodes. Therefore, it is possible to accurately determine the presence or absence of vapor in the fuel, and to accurately determine when vapor has occurred in the fuel. Can be detected.

  Further, in this embodiment, since it is determined that vapor is generated in the fuel when the fuel temperature is in a high temperature region that is equal to or higher than the predetermined temperature and the output fluctuation of the alcohol concentration sensor 41 is equal to or higher than the predetermined value, the fuel temperature is When the output of the alcohol concentration sensor 41 fluctuates relatively small due to a low temperature range where the vapor is not generated due to a temperature lower than a predetermined temperature or for some reason (for example, battery voltage fluctuation or the like), it is erroneously determined that vapor has occurred. This can be prevented, and the detection accuracy of vapor generation can be improved.

  Furthermore, in this embodiment, the fuel injection amount is corrected to be increased when it is determined that vapor has occurred in the fuel, so that it is possible to prevent a decrease in control accuracy of the fuel injection amount due to the generation of vapor. .

  In the above-described embodiment, the presence or absence of vapor generation in the fuel is determined based on the behavior of the output of the alcohol concentration sensor 41. However, the present invention is not limited to this, and based on the behavior of the output of the alcohol concentration sensor 41. Thus, the amount of vapor generated in the fuel may be estimated. Further, the fuel injection amount may be corrected according to the estimated vapor generation amount.

  In the above embodiment, the fuel temperature is detected by the fuel temperature sensor 42. However, the present invention is not limited to this, and the engine operating state (for example, engine rotational speed and engine load) and the vehicle traveling state (for example, vehicle speed and traveling) are not limited thereto. The fuel temperature may be estimated based on time), environmental conditions (for example, outside air temperature), and the like.

  In addition, the present invention is not limited to the intake port injection type engine as shown in FIG. 1, but includes an in-cylinder injection type engine, and both an intake port injection fuel injection valve and an in-cylinder injection fuel injection valve. It can also be applied to dual-injection engines.

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 16 ... Throttle valve, 21 ... Fuel injection valve, 22 ... Spark plug, 23 ... Exhaust pipe, 30 ... Fuel tank, 31 ... Fuel pump, 32 ... Fuel piping, 41 ... alcohol concentration sensor, 42 ... fuel temperature sensor (fuel temperature determination means), 43 ... ECU (vapor determination means, correction means)

Claims (3)

In a control device for an internal combustion engine operable with a plurality of types of fuel having different fuel properties,
A capacitance-type alcohol concentration sensor that detects an alcohol concentration of the fuel by measuring a capacitance between electrodes through which the fuel supplied to the internal combustion engine passes; and
A control device for an internal combustion engine, comprising: vapor determining means for determining a state of occurrence of vapor in the fuel based on a behavior of an output of the alcohol concentration sensor. A fuel temperature determining means for determining the temperature of the fuel;
The vapor determining means determines that vapor has occurred in the fuel when the fuel temperature determined by the fuel temperature determining means is in a high temperature region that is equal to or higher than a predetermined temperature and the output fluctuation of the alcohol concentration sensor is equal to or higher than a predetermined value. The control device for an internal combustion engine according to claim 1, further comprising means.   3. The control device for an internal combustion engine according to claim 1, further comprising correction means for correcting the fuel injection amount to be increased when it is determined by the vapor determination means that vapor has occurred in the fuel. .

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