Biofuel blend ratio estimation device and biofuel blend ratio estimation method

Abstract

To estimate a biofuel mixture ratio using a crank angle sensor.SOLUTION: An integral value calculation unit 105 of a biofuel mixture ratio estimation unit 100 integrates a positive crank angular acceleration α to calculate an angular acceleration integral value Σα. A deviation calculation unit 106 calculates an integral value deviation DΣα, which is the difference between the angular acceleration integral value Σα and a reference value ΣαR, and a calorific value difference calculation unit 108 uses a calorific value difference map 106 to calculate a calorific value difference Cd from the integrated value deviation DΣα. A mixture ratio calculation unit 111 uses a mixture ratio map 112 to calculate a mixture ratio Mr from the calorific value difference Cd.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a biofuel blending ratio estimation device and a biofuel blending ratio estimation method. [Background technology]

[0002] Towards a carbon-neutral society, the use of biofuels that have a low environmental impact is expanding. For example, biofuel blend diesel, which is made by blending biodiesel fuel made from rapeseed oil or waste cooking oil with diesel, is being used as fuel for diesel engines.

[0003] Biodiesel fuel has a smaller calorific value than diesel fuel. For this reason, it is desirable to control the fuel injection amount and fuel injection timing according to the ratio (mixture ratio) of biodiesel fuel mixed with diesel fuel.

[0004] In the case of a diesel particulate filter (DPF) that collects particulate matter (PM) such as soot in exhaust gas, the amount of PM accumulated in the DPF is estimated from operating conditions such as the amount of fuel injection, and the regeneration control of the DPF is performed each time the estimated amount of PM accumulated in the DPF reaches a predetermined amount. The regeneration control of the DPF is performed by performing a post-injection of fuel to burn unburned fuel with an oxidation catalyst or the like installed upstream of the DPF. The larger the mixture ratio of biodiesel fuel, the less soot is generated by combustion. For this reason, when adaptation is performed on the assumption that diesel is used, if a fuel with a high mixture ratio of biodiesel fuel is used, the estimated amount of PM accumulated reaches a predetermined amount before the actual amount of PM accumulated reaches a predetermined amount, and excessive regeneration control is performed. Since biodiesel fuel is less volatile than diesel, there is a possibility that oil dilution caused by post-injection will progress. For this reason, it is desirable to suppress excessive regeneration control to improve fuel efficiency and suppress the progress of oil dilution, and it is preferable to change the control constant (adaptation constant) when estimating the amount of PM accumulated according to the mixture ratio of biodiesel fuel.

[0005] Japanese Patent Laid-Open Publication No. 2011-149297 (Patent Document 1) discloses that the amount of heat generated is determined from the in-cylinder pressure detected by a fuel pressure sensor (in-cylinder pressure sensor) and the blend ratio of biodiesel fuel is specified. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2011-149297 A Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, the amount of heat generated is calculated from the cylinder pressure to determine the biodiesel fuel blend ratio, but in an internal combustion engine that does not have an internal cylinder pressure sensor, the blend ratio cannot be determined. However, a typical electronically controlled internal combustion engine is equipped with a crank angle sensor to detect the rotation speed of the internal combustion engine.

[0008] The present disclosure aims to estimate the mixing ratio of biofuel using a crank angle sensor. [Means for solving the problem]

[0009] The biofuel blending ratio estimation device disclosed herein estimates the blending ratio of biofuel blended into fuel supplied to an internal combustion engine. The biofuel blending ratio estimation device includes a crank angle sensor that detects a crank angle of the internal combustion engine, a crank angular acceleration calculation unit that calculates a crank angular acceleration based on the crank angle, an integral value calculation unit that calculates an angular acceleration integral value by integrating positive crank angular acceleration of the crank angular acceleration, a reference value storage unit that stores a reference value that is an angular acceleration integral value of a reference fuel, a deviation calculation unit that calculates an integral value deviation that is the difference between the angular acceleration integral value calculated by the integral value calculation unit and the reference value, a heat generation amount difference calculation unit that calculates a heat generation amount difference based on the integral value deviation, and a blending ratio calculation unit that calculates the blending ratio based on the heat generation amount difference.

[0010] According to this configuration, the crank angular acceleration calculation unit calculates the crank angular acceleration based on the crank angle detected by the crank angle sensor. The integral value calculation unit calculates an angular acceleration integral value by integrating positive crank angular accelerations of the crank angular accelerations. The reference value storage unit stores a reference value which is an angular acceleration integral value for a reference fuel. The deviation calculation unit calculates an integral value deviation which is the difference between the angular acceleration integral value calculated by the integral value calculation unit and the reference value read from the reference value storage unit. The heat generation amount difference calculation unit calculates a heat generation amount difference based on the integral value deviation. The mixing ratio calculation unit calculates a mixing ratio based on the heat generation amount difference.

[0011] When the heat value of the fuel burning in the cylinder of the internal combustion engine decreases, the output torque decreases, and the angular acceleration integral value obtained by integrating the positive crank angular acceleration of the crank angular acceleration decreases. The angular acceleration integral value calculated by the integral value calculation unit can be regarded as a parameter representing the heat value of the fuel. An integral value deviation, which is the difference between the angular acceleration integral value calculated by the integral value calculation unit and a reference value read from the reference value storage unit, is a parameter corresponding to the heat value difference between the fuel supplied to the internal combustion engine and the reference fuel. The heat value difference calculation unit calculates the heat value difference from the integral value deviation calculated by the deviation calculation unit. The mixture ratio calculation unit can calculate the mixture ratio based on this heat value difference. Therefore, the mixture ratio of the biofuel can be estimated from the crank angle detected by the crank angle sensor.

[0012] Preferably, the biofuel blending ratio estimation device includes a heat generation amount difference map having parameters of the rotation speed of the internal combustion engine, the fuel injection amount, and the integral value deviation, and the heat generation amount difference calculation unit may calculate the heat generation amount difference using the heat generation amount difference map.

[0013] The biofuel blending ratio estimating device may be provided with a blending ratio map using the fuel injection amount and the heat generation amount difference as parameters, and the blending ratio calculation unit may calculate the blending ratio using the blending ratio map.

[0014] According to these configurations, it is possible to calculate the mixture ratio with high accuracy even in operating conditions in which the rotation speed or fuel injection amount differs.

[0015] Preferably, the biofuel mixing ratio estimation device includes a steady state determination unit which determines whether or not an amount of change in the rotational speed is within a predetermined range, and when the steady state determination unit determines that the amount of change is within the predetermined range, the integral value calculation unit calculates the angular acceleration integral value.

[0016] According to this configuration, the mixture ratio is calculated in an operating state where the fluctuation of the angular acceleration integral value is small, so that the calculation accuracy of the mixture ratio can be improved.

[0017] Preferably, the biofuel blending ratio estimating device may be configured such that the integral calculation unit calculates the angular acceleration integral when the internal combustion engine is operated for the first time after the fuel tank is filled with fuel.

[0018] Once refueling has been performed, the mixture ratio of the fuel supplied to the internal combustion engine will not change until the next refueling. With this configuration, the mixture ratio is calculated based on the angular acceleration integral value when the internal combustion engine is operated for the first time after refueling has been performed in the fuel tank, so the load for calculating the mixture ratio can be reduced.

[0019] Preferably, when an excess air ratio in a cylinder of the internal combustion engine is equal to or greater than a predetermined value larger than 1, the integral calculation unit may calculate the angular acceleration integral value.

[0020] When the excess air ratio in the cylinder is small, it becomes difficult for the fuel in the cylinder to burn completely. In particular, when the excess air ratio is less than 1, there is a shortage of air required for fuel combustion. For this reason, when the excess air ratio is small, the calorific value difference cannot be calculated with high accuracy. With this configuration, when the excess air ratio is equal to or greater than a predetermined value greater than 1, the angular acceleration integral is calculated, so the mixture ratio can be calculated with high accuracy.

[0021] Preferably, the reference fuel is a fuel to which no biofuel is mixed, and the reference value storage unit may store a reference value that is an angular acceleration integral value for a fuel to which no biofuel is mixed.

[0022] According to this configuration, the reference value can be set (adapted) using normal fuel (not mixed with biofuel), so setting the reference value becomes relatively easy.

[0023] The biofuel blending ratio estimation method disclosed herein estimates the blending ratio of biofuel blended into fuel supplied to an internal combustion engine. The biofuel blending ratio estimation method includes the steps of calculating a crank angular acceleration from a crank angle of the internal combustion engine, calculating an angular acceleration integral value by integrating the positive crank angular acceleration, reading a reference value which is an angular acceleration integral value of a reference fuel, calculating an integral value deviation which is a difference between the calculated angular acceleration integral value and the read reference value, calculating a heat generation difference using the integral value deviation, and calculating the blending ratio from the heat generation amount difference.

[0024] According to this configuration, the crank angular acceleration is calculated from the crank angle of the internal combustion engine, and an integral value deviation is calculated, which is the deviation between an angular acceleration integral value obtained by integrating the positive crank angular acceleration and a reference value. The mixing ratio is then calculated from the heat generation amount difference calculated using the integral value deviation. Therefore, the mixing ratio of biofuel can be estimated from the crank angle of the internal combustion engine.

[0025] Preferably, the step of calculating the heat generation difference calculates the heat generation difference from the rotation speed of the internal combustion engine, the fuel injection amount, and the integral value deviation, and the step of calculating the mixing ratio calculates the mixing ratio from the fuel injection amount and the heat generation difference.

[0026] According to this configuration, it is possible to calculate the mixture ratio with high accuracy even in operating conditions in which the rotation speed or fuel injection amount differs. Effect of the Invention

[0027] According to the present disclosure, the mixing ratio of biofuel can be estimated using a crank angle sensor. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is an overall configuration diagram of an engine 1 according to the present embodiment. [Diagram 2] 2 is a diagram showing functional blocks of a biofuel blending ratio estimation unit 100 configured in an engine ECU 200. FIG. [Diagram 3] FIG. 4 is a diagram showing an example of a crank angular acceleration α. [Figure 4] FIG. 13 is a diagram showing an example of a map of reference values ​​ΣαR stored in a reference value storage unit 107. [Diagram 5] FIG. 4 is a diagram showing an example of a heat generation amount difference map 109. [Figure 6] FIG. 4 is a diagram showing an example of a mixture ratio map 112. [Figure 7] 4 is a flowchart showing a mixture ratio estimation control process executed by the engine ECU 200. [Figure 8] 4 is a flowchart showing an interrupt request process for the mixture ratio estimation control executed by the engine ECU. [Figure 9] 10 is a flowchart showing a mixture ratio estimation control process executed by engine ECU 200 in Modification 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and the description thereof will not be repeated.

[0030] 1 is an overall configuration diagram of an engine 1 according to this embodiment. The engine 1 is a compression self-ignition type internal combustion engine (diesel engine) that injects fuel from a fuel injection valve (injector) 14 into a combustion chamber formed in a cylinder (cylinder) 12 of an engine body 10, and performs compression self-ignition. In this embodiment, the engine 1 has four cylinders. An air cleaner 22, an intercooler 24, and an intake throttle valve (electronically controlled throttle) 26 are provided in an intake passage 20 of the engine 1. Fresh air from which foreign matter has been removed by the air cleaner 22 is supercharged (compressed) by a compressor 32 of a turbocharger 30, cooled by the intercooler 24, supplied to an intake manifold 28, and supplied to each combustion chamber from an intake port.

[0031] Exhaust gas discharged from the combustion chamber is collected in an exhaust manifold 50 and released to the outside air via an exhaust passage 52. A portion of the exhaust gas is recirculated to the intake manifold 28 via an EGR (Exhaust Gas Recirculation) passage 60. An EGR cooler 62 and an EGR valve 64 are provided in the EGR passage 60.

[0032] In the exhaust passage 52, from the upstream side, the turbine 34 of the turbocharger 30, an oxidation catalyst 70, and a DPF (Diesel Particulate Filter) 72 are provided. The DPF 72 collects particulate matter (PM) in the exhaust gas and purifies the exhaust gas by appropriately burning and removing the collected particulate matter. Although not shown, a NOx storage-reduction catalyst (NSR (NOx Storage-Reduction) catalyst) is provided downstream of the DPF 72. Note that a urea addition valve and a selective reduction catalyst may be provided instead of the NOx storage-reduction catalyst.

[0033] Fuel is stored in a fuel tank 40. The fuel in the fuel tank 40 is pressure-fed by a high-pressure fuel pump 41 through a fuel passage 42 to a common rail 43. The high-pressure fuel stored in the common rail 43 is injected from the injector 14 into the combustion chamber (inside the cylinder).

[0034] The engine 1 further includes an engine ECU (Electronic Control Unit) 200. The engine ECU 200 includes a CPU (Central Processing Unit) 220, a memory 240 consisting of a ROM (Read Only Memory) for storing processing programs and the like and a RAM (Random Access Memory) for temporarily storing data, and an input / output port (not shown) for inputting and outputting various signals, and executes predetermined arithmetic processing based on information stored in the memory 240 and information from various sensors, and controls the injector 14, the intake throttle valve 26, the high-pressure fuel pump 41, and the like.

[0035] The various sensors include, for example, a crank angle sensor 121, an accelerator pedal sensor 122, an intake air amount sensor 123, a fuel level gauge 124, and the like. The crank angle sensor 121 detects the crank angle θ of the engine 1. The accelerator pedal sensor 122 detects the amount of accelerator pedal operation (hereinafter also referred to as “accelerator opening”) AP by the user. The intake air amount sensor 123 detects the intake air amount Ga. The fuel level gauge 124 detects the amount of fuel stored in the fuel tank 40.

[0036] In the engine 1 configured as described above, for example, biodiesel-mixed diesel fuel, which is made by mixing diesel fuel with biodiesel fuel made from rapeseed oil or waste edible oil, may be used as fuel. Biodiesel fuel has a smaller calorific value than diesel fuel. Biodiesel fuel also produces less soot when burned. For this reason, it is desirable to control the fuel injection amount and fuel injection timing, estimate the amount of PM accumulation in the DPF, and so on, depending on the ratio (mixture ratio) of biodiesel fuel mixed with diesel fuel. In this embodiment, the mixture ratio of biodiesel fuel is calculated using the crank angle θ detected by the crank angle sensor 121.

[0037] 2 is a diagram showing functional blocks of a biofuel blending ratio estimation unit 100 configured in the engine ECU 200. The biofuel blending ratio estimation unit 100 corresponds to the biofuel blending ratio estimation device of the present disclosure.

[0038] A rotation speed calculation section (NE calculation section) 101 calculates the rotation speed (revolutions per minute (rpm)) NE of the engine 1 based on the crank angle θ detected by the crank angle sensor 121. A fuel injection amount calculation section (Qf calculation section) 102 calculates a fuel injection amount Qf (injection amount per injection (mm 3 The calculated fuel injection amount Qf is sent to the injector driving unit, and fuel equivalent to the fuel injection amount Qf is injected from the injector 14.

[0039] The steady state determination unit 103 determines whether the change amount ΔNE of the rotation speed NE is within a predetermined range. For example, when "|previous value of the rotation speed NE-current value of the rotation speed NE|<threshold value T1", it is determined that the steady state is present.

[0040] A crank angular acceleration calculation unit (α calculation unit) 104 calculates the crank angular acceleration α based on the crank angle θ detected by the crank angle sensor 121. For example, the crank angular acceleration calculation unit 104 calculates the crank angular acceleration α by calculating the crank angular velocity ω from the crank angle θ and differentiating the crank angular velocity ω with respect to time.

[0041] When the steady state determination unit 103 determines that the engine is in a steady state, the integral value calculation unit (Σα calculation unit) 105 integrates the positive crank angular acceleration α to calculate the angular acceleration integral value Σα. FIG. 3 is a diagram showing the crank angular acceleration α. ​​In this embodiment, the engine 1 is a four-cylinder / four-cycle engine, and a combustion stroke is performed every 180° CA (180° crank angle). In FIG. 3, the solid line indicates the crank angular acceleration α when biofuel-mixed diesel is used, and the angular acceleration integral value Σα calculated by the integral value calculation unit 105 corresponds to the area of ​​the shaded portion in FIG. 3. In this embodiment, the average value of ten combustion strokes (combustion + expansion stroke) is calculated as the angular acceleration integral value Σα, but it may be the average value of the combustion strokes in a predetermined time.

[0042] The deviation calculation unit (DΣα calculation unit) 106 calculates an integral deviation DΣα, which is the difference between the angular acceleration integral value Σα and the reference value ΣαR. The reference value ΣαR is an angular acceleration integral value for the reference fuel, and is stored in the reference value storage unit (ΣαR storage unit) 107. FIG. 4 is a diagram showing an example of a map of the reference value ΣαR stored in the reference value storage unit 107. The reference value storage unit 107 is configured in the memory 240. In this embodiment, the reference fuel is diesel (not mixed with biodiesel fuel). The reference value ΣαR is a value obtained by integrating the positive crank angular acceleration α when the engine 1 is operated using the reference fuel. Since the calorific value of diesel is larger than that of diesel mixed with biofuel, the reference value ΣαR corresponds to the area surrounded by the dashed line in FIG. 3, and is obtained in advance by an experiment or the like. As shown in FIG. 4, in this embodiment, the reference value ΣαR is stored in the reference value storage unit 107 as a map with the fuel injection amount Qf and the rotation speed NE as parameters, but the map may also be one with only the fuel injection amount Qf as a parameter.

[0043] 4 based on the fuel injection amount Qf and the rotation speed NE. Then, the deviation calculation unit 106 calculates an integral value deviation DΣα, which is the difference between the angular acceleration integral value Σα and the reference value ΣαR. In this embodiment, the integral value deviation DΣα (=ΣαR-Σα) is calculated by subtracting the angular acceleration integral value Σα from the reference value ΣαR.

[0044] The heat generation amount difference calculation unit (Cd calculation unit) 108 calculates the heat generation amount difference Cd using a heat generation amount difference map (Cd map) 109. FIG. 5 is a diagram showing an example of the heat generation amount difference map 109. The heat generation amount difference map 109 is a so-called three-dimensional map, and is a map with the rotation speed NE, the fuel injection amount Qf, and the integral value deviation DΣα as parameters. In this embodiment, as shown in FIG. 5, a two-dimensional map with the fuel injection amount Qf and the integral value deviation DΣα as parameters is stored in the memory 240 for each rotation speed NE. The heat generation amount difference calculation unit 108 calculates the heat generation amount difference Cd using the heat generation amount difference map 109 from the rotation speed NE, the fuel injection amount Qf, and the integral value deviation DΣα. Note that for points (values) not included in the heat generation amount difference map 109, the heat generation amount difference Cd may be calculated by linear interpolation. The heat generation amount difference map 109 is set in advance by simulation, experiment, or the like.

[0045] The mixing ratio calculation unit (Mr calculation unit) 111 calculates the mixing ratio Mr using a mixing ratio map (Mr map) 112. FIG. 6 is a diagram showing an example of the mixing ratio map 112. The mixing ratio map 112 is a map with the fuel injection amount Qf and the heat generation amount difference Cd as parameters. The mixing ratio calculation unit 111 calculates the mixing ratio Mr from the fuel injection amount Qf and the heat generation amount difference Cd using the mixing ratio map 112. The mixing ratio is the proportion of biodiesel fuel mixed into diesel, and can be expressed in, for example, "%". The mixing ratio map 112 is set in advance by simulation, experiment, or the like.

[0046] The constant changing section 113 uses the mixture ratio Mr calculated by the mixture ratio calculating section 111 to change the fuel injection amount Qf, the fuel injection timing, and the control constants (adaptation constants) of the PM accumulation amount estimation control.

[0047] 7 is a flowchart showing the mixture ratio estimation control process executed by the engine ECU 200. This flowchart is interrupted at predetermined intervals while the engine 1 is in operation. In step (hereinafter, step is abbreviated as "S") 10, the steady state determination unit 103 determines whether the operating state of the engine 1 is in a steady state. If "|previous value of rotation speed NE-current value of rotation speed NE|<threshold value T1", it is determined that the engine 1 is in a steady state, and the process proceeds to S11. If "|previous value of rotation speed NE-current value of rotation speed NE|≧threshold value T1", it is determined that the engine 1 is in a steady state, and the process proceeds to S11.

[0048] In S11, the integral value calculation unit 105 integrates the positive crank angular acceleration α to calculate the angular acceleration integral value Σα, and then the process proceeds to S12. Note that the crank angular acceleration α is calculated by the crank angular acceleration calculation unit 104 calculating the crank angular velocity ω from the crank angle θ detected by the crank angle sensor 121 and differentiating the crank angular velocity ω with respect to time in a routine (not shown, for example, a rotation speed NE calculation routine).

[0049] When the steady state determination section 103 determines that the steady state is present, an integral value calculation section (Σα calculation section) 105 integrates the positive crank angular acceleration α to calculate an angular acceleration integral value Σα.

[0050] In S12, the deviation calculation unit 106 reads out the reference value ΣαR stored in the reference value storage unit 107 (memory 240), and calculates an integral value deviation DΣα which is the difference between the angular acceleration integral value Σα and the reference value ΣαR.

[0051] In the next S13, the heat generation amount difference calculation section 108 calculates the heat generation amount difference Cd from the rotation speed NE, the fuel injection amount Qf, and the integral value deviation DΣα using the heat generation amount difference map 109, and the process proceeds to S14.

[0052] In S14, the mixture ratio calculation section 111 calculates the mixture ratio Mr from the fuel injection amount Qf and the heat generation amount difference Cd using the mixture ratio map 112, and then ends the current routine.

[0053] When the heat value of the fuel burning in the combustion chamber (cylinder) of the engine 1 decreases, the output torque decreases, and the angular acceleration integral value Σα (area of ​​the shaded portion in FIG. 3) obtained by integrating the positive crank angular acceleration α of the crank angular acceleration α decreases. The angular acceleration integral value Σα calculated by the integral value calculation unit 105 can be regarded as a parameter representing the heat value of the fuel. An integral value deviation DΣα, which is the difference between the angular acceleration integral value Σα calculated by the integral value calculation unit 105 and the reference value ΣαR read from the reference value storage unit 107, is a parameter corresponding to the heat value difference between the fuel supplied to the engine 1 and the reference fuel. The heat value difference calculation unit 108 calculates the heat value difference Cd from the integral value deviation DΣα calculated by the deviation calculation unit 106 using the heat value difference map 109. Based on this heat value difference Cd, the mixture ratio calculation unit 111 can calculate the mixture ratio Mr using the mixture ratio map 112.

[0054] According to the above embodiment, the mixing ratio Mr of biofuel-mixed diesel can be estimated from the crank angle θ detected by the crank angle sensor 121. In the above embodiment, the crank angle sensor 121 is provided in the engine 1 in order to detect (calculate) the rotation speed NE, and the mixing ratio Mr of biofuel-mixed diesel can be estimated without providing a new combustion pressure sensor (cylinder pressure sensor) or the like.

[0055] (Variation 1) Once the fuel tank 40 has been refueled, the mixture ratio of the fuel (biofuel-mixed diesel) supplied to the engine 1 will not change until the next refueling. Therefore, when the engine 1 is operated for the first time after the fuel tank 40 has been refueled, the mixture ratio estimation control process of Fig. 7 is executed, thereby reducing the processing load (computation load) of the engine ECU 200.

[0056] In the above embodiment, the process (flowchart) of the mixture ratio estimation control in FIG. 7 is interrupted at a predetermined time interval during the operation of the engine 1. In the first modification, the mixture ratio estimation control is processed by an interrupt request. FIG. 8 is a flow chart showing the interrupt request process of the mixture ratio estimation control executed by the engine ECU 200. This flow chart is executed when the engine 1 is started. For example, when the ignition switch (start switch) is turned on and the engine 1 is started, in S20, it is determined whether or not refueling has been performed to the fuel tank 40. In this embodiment, it is determined whether or not refueling has been performed using the amount of fuel in the fuel tank 40 detected by the fuel level gauge 124. For example, when the amount of fuel at the current start of the engine 1 is greater than the amount of fuel at the previous time when the engine 1 was stopped (when the ignition switch was turned off), it is determined that refueling has been performed. Note that if there is a history of the fuel lid (fail lid) being opened between the stop of the engine 1 and the start of the engine 1, it may be determined that refueling has been performed. If it is determined in S20 that fuel has been refilled into the fuel tank 40, the process proceeds to S21. If it is determined that fuel has not been refilled into the fuel tank 40, the current routine is terminated.

[0057] In S21, it is determined whether or not a predetermined period of time has elapsed since the start of the engine 1. The predetermined period of time is set to be a sufficient time for the fuel stored in the fuel tank 40 before refueling and the biofuel-mixed diesel fuel that has been refueled to mix together. When the engine 1 is mounted on a vehicle, the fuel in the fuel tank 40 is expected to be stirred by vibrations during driving, so the predetermined period of time may be several minutes after the start of the engine 1. After the start of the engine 1, S21 is repeatedly processed until the predetermined period of time has elapsed, and when the predetermined period of time has elapsed since the start of the engine 1, a positive determination is made in S21 and the process proceeds to S22.

[0058] In S22, an interrupt request for the mixture ratio estimation control is made, and the current routine is terminated. In this modified example 1, when the interrupt request is made in S22, the process of the mixture ratio estimation control in FIG.

[0059] According to this modification 1, the mixture ratio Mr is calculated based on the angular acceleration integral value Σα when the engine 1 is operated for the first time after fuel is supplied to the fuel tank 40, so that the computational load for calculating the mixture ratio Mr can be reduced.

[0060] (Variation 2) When the excess air ratio in the combustion chamber (cylinder) of the engine 1 is small, it becomes difficult to completely burn the fuel in the combustion chamber. In particular, when the excess air ratio is less than 1, there is a shortage of air required for fuel combustion. For this reason, when the excess air ratio is small, the calorific value difference Cd between the biofuel-mixed diesel and the reference fuel cannot be calculated with high accuracy.

[0061] For example, when reducing and purifying NOx stored in the NSR catalyst, the intake throttle valve 26 is closed and the fuel injection amount Qf is increased to make the intake excess ratio smaller than 1 and generate a reducing atmosphere. In this case, part of the fuel supplied to the combustion chamber is discharged as unburned fuel for NOx reduction, so the heat generation amount difference Cd cannot be calculated accurately based on the angular acceleration integral value Σα. Also, even if the excess air ratio is greater than 1, complete combustion is difficult when the excess air ratio is small, and the heat generation amount difference Cd cannot be calculated accurately based on the angular acceleration integral value Σα.

[0062] In the second modification, when the excess air ratio is equal to or greater than the air excess ratio at which the fuel is completely combusted satisfactorily, the mixture ratio Mr is calculated using the angular acceleration integral value Σα, thereby calculating the mixture ratio Mr with high accuracy. FIG 9 is a flowchart showing the process of the mixture ratio estimation control executed by the engine ECU 200 in the second modification. This flowchart is interrupted at predetermined intervals while the engine 1 is in operation. This flowchart is obtained by adding S40 to the flowchart in FIG 7 in the above embodiment, and S10 to S14 are the same as those in the flowchart in FIG 7, so their description will be omitted.

[0063] If the engine is in a steady state (|previous value of rotation speed NE-current value of rotation speed NE|<threshold T1) and a positive determination is made in S10, then in S40 it is determined whether or not the excess air ratio λ is greater than a predetermined value A. The excess air ratio λ is determined, for example, from the intake air amount Ga detected by intake air amount sensor 123 and the fuel injection amount Qf. Alternatively, a λ sensor (full-range air-fuel ratio sensor) may be provided in exhaust passage 52 to detect the excess air ratio λ. If the excess air ratio λ is smaller than predetermined value A (for example, 1.2), a negative determination is made and the current routine is terminated. If the excess air ratio λ is greater than predetermined value A, a positive determination is made and the routine proceeds to S11.

[0064] According to the second modification, when the excess air ratio is equal to or greater than a predetermined value greater than 1, the angular acceleration integral value Σα is calculated to calculate the mixture ratio Mr, so that the mixture ratio Mr can be estimated with high accuracy.

[0065] In the above embodiment, diesel fuel is used as the reference fuel. However, diesel fuel mixed with biodiesel fuel having a predetermined blend ratio may be used as the reference fuel. For example, diesel fuel mixed with biodiesel fuel, so-called B5, which is a blend of 5% biodiesel fuel, may be used as the reference fuel, and the blend ratio may be estimated by setting the reference value ΣαR (FIG. 4), the calorific value difference map (FIG. 5), and the blend ratio map (FIG. 6).

[0066] In the above embodiment, a diesel engine has been described as the engine 1, but the engine 1 may be a gasoline engine (spark ignition engine). In a gasoline engine, a biofuel blended gasoline in which bioethanol or bio-ETBE (ethyl tertiary-butyl ether) is blended with gasoline is used. The calorific value of bioethanol and bio-ETBE is smaller than that of gasoline, and the blend ratio of biofuel (bioethanol, bio-ETBE) can be estimated in the biofuel blended gasoline in the same way as in the above embodiment.

[0067] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the description of the embodiments described above, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0068] 1 engine, 10 engine body, 12 cylinder, 14 injector, 20 intake passage, 22 air cleaner, 24 intercooler, 26 intake throttle valve, 28 intake manifold, 30 turbocharger, 32 compressor, 34 turbine, 40 fuel tank, 41 high pressure fuel pump, 42 fuel passage, 43 common rail, 50 exhaust manifold, 52 exhaust passage, 60 ERG passage, 62 EGR cooler, 64 EGR valve, 70 oxidation catalyst, 72 DPF, 100 biofuel blend ratio estimation unit, 101 rotation speed calculation unit, 102 fuel injection amount calculation unit, 103 steady state determination unit, 104 crank angular acceleration calculation unit, 105 integral value calculation unit, 106 deviation calculation unit, 107 reference value storage unit, 108 heat generation amount difference calculation unit, 109 Heat generation difference map, 111 mixture ratio calculation unit, 112 mixture ratio map, 121 crank angle sensor, 122 accelerator pedal sensor, 123 intake air amount sensor, 124 fuel level gauge, 200 engine ECU, 210 CPU, 220 memory.

Claims

1. A biofuel blending ratio estimation device that estimates a blending ratio of a biofuel blended into a fuel supplied to an internal combustion engine, comprising: a crank angle sensor for detecting a crank angle of the internal combustion engine; a crank angular acceleration calculation unit that calculates a crank angular acceleration based on the crank angle; an integral value calculation unit that calculates an angular acceleration integral value by integrating the positive crank angular acceleration of the crank angular acceleration; a reference value storage unit that stores a reference value that is the integral value of angular acceleration for a reference fuel; a deviation calculation unit that calculates an integral deviation, which is a difference between the angular acceleration integral value calculated by the integral calculation unit and the reference value; a heat generation amount difference calculation unit that calculates a heat generation amount difference based on the integral value deviation; and a mixing ratio calculation unit that calculates the mixing ratio based on the calorific value difference.

2. a heat generation amount difference map having parameters of the rotation speed of the internal combustion engine, the fuel injection amount, and the integral value deviation, The biofuel blending ratio estimating device according to claim 1 , wherein the heat generation amount difference calculating unit calculates the heat generation amount difference by using the heat generation amount difference map.

3. a mixture ratio map having a fuel injection amount of the internal combustion engine and the heat generation amount difference as parameters, The biofuel blending ratio estimation device according to claim 1 , wherein the blending ratio calculation unit calculates the blending ratio by using the blending ratio map.

4. a steady state determination unit that determines whether an amount of change in the rotation speed of the internal combustion engine is within a predetermined range; The biofuel mixing ratio estimation device according to claim 1 , wherein when the steady state determination unit determines that the amount of change is within the predetermined range, the integral calculation unit calculates the angular acceleration integral value.

5. 5. The biofuel mixing ratio estimation device according to claim 1, wherein the integral value calculation unit calculates the angular acceleration integral value when the internal combustion engine is operated for the first time after a fuel tank is filled with fuel.

6. The biofuel mixing ratio estimating device according to claim 1 , wherein the integral calculation unit calculates the angular acceleration integral when an excess air ratio in a cylinder of the internal combustion engine is equal to or greater than a predetermined value greater than 1.

7. The reference fuel is a fuel that is not blended with biofuel, 7. The biofuel blending ratio estimation device according to claim 1, wherein the reference value storage unit stores a reference value that is the angular acceleration integral value of a fuel that does not contain biofuel.

8. A biofuel blending ratio estimation method for estimating a blending ratio of a biofuel blended into a fuel supplied to an internal combustion engine, comprising: calculating a crank angular acceleration from a crank angle of the internal combustion engine; A step of integrating the positive crank angular acceleration to calculate an angular acceleration integral value; reading out a reference value which is the integral of angular acceleration for a reference fuel; calculating an integral deviation which is a difference between the calculated angular acceleration integral value and the read reference value; Calculating a heat generation difference using the integral value deviation; and calculating the mixing ratio from the calorific value difference.

9. the step of calculating the heat generation amount difference includes calculating the heat generation amount difference from a rotation speed of the internal combustion engine, a fuel injection amount, and the integral value deviation; The biofuel blending ratio estimation method according to claim 8 , wherein the step of calculating the blending ratio calculates the blending ratio from the fuel injection amount and the heat generation amount difference.

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