Engine control method and engine system

Abstract

To accurately estimate properties of fuel to be supplied to an engine.SOLUTION: In a control method for an engine 100, during motoring, an injector 6 injects fuel for determination into a cylinder 11 at a specific time point after closing of an intake valve 21, and a cylinder inner pressure sensor SW4 outputs to a controller (ECU 10) a signal corresponding to the pressure in the cylinder at a time point of elapse of a specific crank angle period at least from a time point of fuel injection. The controller determines properties of the fuel injected by the injector by comparing a measured pressure value with a pressure value that is stored beforehand and is a pressure value in the cylinder at a time point of elapse of the specific crank angle period after standard fuel is injected into the cylinder at a specific time point.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an engine control method and an engine system. [Background technology]

[0002] Patent Document 1 describes a technique for creating a heat release rate waveform for a low-temperature oxidation reaction by setting the fuel reaction start timing to the advanced side (the temperature at which the low-temperature oxidation reaction can start) depending on the period during which the fuel floats after being injected into the cylinder, and the longer the floating period, the more advanced the reaction start timing (the lower the reaction start temperature for the low-temperature oxidation reaction).This technique enables accurate diagnosis of the combustion state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-234727 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, fuel supplied to automobile engines contains various additives, and the types and blending ratios of these additives vary depending on the manufacturer. As a result, the properties of fuel supplied to automobile engines are not always the same. In addition, biofuels may also be supplied to engines. The properties of biofuels may differ significantly from those of fossil fuels. In the future, it is expected that fuels with various properties will be supplied to engines.

[0005] On the other hand, engine controllers control the engine by presetting the fuel injection timing and fuel injection amount for optimal combustion based on the properties of standard fuel. If the properties of the fuel supplied to a vehicle change from the standard fuel, it can cause misfires or sudden combustion. Therefore, there is a demand for accurate determination of the properties of the fuel supplied to the engine.

[0006] The technology disclosed herein makes it possible to accurately determine the properties of fuel supplied to an engine. [Means for solving the problem]

[0007] The technology disclosed herein relates to an engine control method. This engine control method includes: During engine motoring, an injector injects fuel for determination into a cylinder of the engine at a specific time point after an intake valve of the cylinder closes; The cylinder pressure sensor includes at least The injector for determination is inserted into the cylinder. fuel of injection did time (i.e., at the time of fuel injection) outputting a signal corresponding to the pressure in the cylinder at a time when a specific crank angle period has elapsed since the time when the signal was received, to the controller; The controller determines the properties of the fuel injected by the injector by comparing the pressure value measured by the in-cylinder pressure sensor with a pre-stored pressure value, which is the pressure value in the cylinder at a point in time when the specific crank angle period has elapsed after standard fuel is injected into the cylinder at the specific time point.

[0008] According to this configuration, the injector injects fuel for determination into the cylinder while the engine is motoring. Here, "engine motoring" refers to a state in which the engine crankshaft is rotated by a drive source external to the engine, such as a generator, an electric motor, or a starter motor. This engine motoring corresponds to the time when the engine is started. In an internal combustion engine vehicle, engine starting corresponds to the time when the occupant turns on the ignition switch of the vehicle, or in a hybrid vehicle, the time when the engine is started, for example, to generate electricity or to satisfy a required torque.

[0009] During engine motoring, the cylinder undergoes intake, compression, expansion, and exhaust strokes due to external driving force. The injector injects fuel for determination into the cylinder at a specific point in time during the compression stroke after the intake valve closes. The "fuel for determination" may be a small amount of fuel that does not cause a high-temperature oxidation reaction even when the piston reaches near top dead center of compression. The "fuel for determination" is fuel supplied into the cylinder to determine its fuel properties.

[0010] As the compression stroke progresses, the pressure inside the cylinder gradually increases. Over time, the fuel injected into the cylinder undergoes fragmentation, atomization, evaporation, and mixing with air, leading to a low-temperature oxidation reaction. The amount of heat generated varies depending on the fuel's properties, such as its specific heat ratio and / or gas constant. This means that the amount of heat generated varies because the initial chemical reaction in the preparation stage for the low-temperature oxidation reaction (e.g., when the in-cylinder gas temperature is 700 K) is different. The initial chemical reaction is the generation of radicals (alkyl peroxides, such as HClO2 and HClO2) through a hydrogen abstraction reaction. Differences in the amount of heat generated change the rate of increase in the pressure inside the cylinder.

[0011] The cylinder pressure sensor outputs a signal to the controller that corresponds to the pressure inside the cylinder at a specific crank angle period after the fuel injection. If the fuel injected by the injector is a fuel that easily generates heat, the pressure value will be relatively high, and if the fuel is a fuel that does not easily generate heat, the pressure value will be relatively low.

[0012] The controller stores the pressure value of a standard fuel in advance. A "standard fuel" is a fuel that corresponds to, for example, K2202 (gasoline for automobiles) or K2204 (diesel for automobiles) specified in the JIS standard. The pressure value of the standard fuel is the pressure value inside the cylinder at a specific crank angle period after the standard fuel is injected into the cylinder at a specific time point. The controller also compares the pressure value measured by the in-cylinder pressure sensor with the pressure value of the standard fuel.

[0013] Specifically, when the measured pressure value is higher than the pressure value of standard fuel, the fuel injected by the injector is a fuel that easily generates heat and is prone to low-temperature oxidation reactions. Therefore, when the engine is running after starting, that is, when the engine is operating by burning the fuel injected into the cylinder, as opposed to motoring, the fuel is prone to high-temperature oxidation reactions. The combustion in the cylinder tends to be abrupt. Also, the combustion noise is likely to be loud.

[0014] On the other hand, if the measured pressure value is lower than the pressure value of the standard fuel, the fuel injected by the injector is a fuel that does not easily generate heat and does not easily undergo low-temperature oxidation reactions. Therefore, when the engine is running after starting, the fuel is likely to burn slowly because it does not easily undergo high-temperature oxidation reactions. This leads to a decrease in engine torque and a decrease in fuel efficiency.

[0015] This technology focuses on the fact that the heat generation rate differs depending on the fuel. The controller compares the pressure value at a specific crank angle period after the fuel injection based on the fact that the rate of pressure rise in the cylinder changes depending on the heat generation rate of the fuel injected into the cylinder. This allows the controller to accurately determine the properties of the fuel supplied to the engine.

[0016] In particular, the determination of fuel properties is performed while the engine is motoring. Because no high-temperature oxidation reaction of the fuel occurs, the controller can determine the fuel properties without being affected by heat or residual gases. This allows the controller to more accurately determine the properties of the fuel supplied to the engine.

[0017] the engine has a plurality of cylinders; The injector injects fuel for determination into the cylinder whose intake valve is first closed after the crankshaft of the engine starts to rotate. do.

[0018] As the engine cycle progresses, the crankshaft speed increases, causing the temperature inside the cylinder to rise. As the temperature inside the cylinder increases, the heat can affect the fuel quality assessment.

[0019] By determining the fuel properties in the cylinder whose intake valve first closes after the engine crankshaft starts rotating, the controller can determine the fuel properties without being affected by heat or residual gases.

[0020] The injector injects fuel for determination into each of a plurality of cylinders as the engine cycle progresses, the in-cylinder pressure sensor outputs a pressure value for each of the plurality of cylinders; The controller compares the average of the pressure values ​​with the pressure value of the standard fuel. do.

[0021] The controller can improve the accuracy of the determination by determining the fuel properties using the average value of multiple pressure values.

[0022] The specific crank angle period becomes shorter with each progression of the cycle. do.

[0023] As mentioned above, the temperature inside the cylinder gradually increases as the engine cycle progresses. This increase in temperature makes the fuel injected into the cylinder more reactive, accelerating the increase in pressure inside the cylinder. By shortening the specific crank angle period with each cycle, pressure values ​​can be measured that eliminate the influence of temperature increases during multiple cycles. The controller can more accurately determine the properties of the fuel based on the multiple pressure values.

[0024] The specific crank angle period may correspond to a period during which fuel injected from the injector into the cylinder undergoes splitting, atomization, evaporation, and mixing with air, leading to a low-temperature oxidation reaction.

[0025] As mentioned above, this technology determines the properties of fuel by taking advantage of differences in the amount of heat generated in the initial chemical reaction. By matching a specific crank angle period, which corresponds to the time from fuel injection to pressure measurement, with the time it takes for the fuel to undergo splitting, atomization, evaporation, and mixing with air before reaching a low-temperature oxidation reaction, the in-cylinder pressure sensor can measure a pressure value that reflects the amount of heat generated in the initial chemical reaction. The controller can use this pressure value to accurately determine the properties of the fuel. The specific crank angle period may be the period before the piston in the cylinder reaches top dead center of compression.

[0026] The controller may correct at least one of a fuel injection amount and a closing timing of the intake valve according to a property of the fuel after the engine has been started.

[0027] If the fuel injected by the injector is one that undergoes low-temperature oxidation easily, it will be prone to high-temperature oxidation, leading to rapid combustion. If the fuel is one that does not undergo low-temperature oxidation easily, it will be prone to high-temperature oxidation easily, leading to slow combustion.

[0028] The controller corrects at least one of the fuel injection amount and the intake valve closing timing according to the fuel properties, thereby standardizing combustion regardless of the fuel properties. In other words, combustion is equivalent to that of standard fuel, regardless of the fuel properties. This is advantageous for improving the engine's fuel economy and exhaust gas performance. It also helps to suppress an increase in combustion noise.

[0029] The controller may correct the closing timing of the intake valve to the retard side when the measured pressure value is higher than the pressure value of the standard fuel, and correct the closing timing of the intake valve to the advance side when the measured pressure value is lower than the pressure value of the standard fuel.

[0030] If the measured pressure value is higher than the pressure value of the standard fuel, the fuel is relatively prone to heat generation. Therefore, the intake valve closing timing is corrected to the retard side. If the intake valve closing timing is retarded, the temperature inside the cylinder drops, making the fuel less likely to heat up. Even if the fuel is prone to heat generation, combustion will be equivalent to combustion of the standard fuel. Conversely, if the measured pressure value is lower than the pressure value of the standard fuel, the fuel is relatively prone to heat generation. Therefore, the intake valve closing timing is corrected to the advance side. If the intake valve closing timing is advanced, the temperature inside the cylinder rises, making the fuel more likely to heat up. Even if the fuel is less likely to heat up, combustion will be equivalent to combustion of the standard fuel. Note that the intake valve closing timing is set to be after the intake bottom dead center.

[0031] The controller may correct the intake valve closing timing so that the higher the measured pressure value is relative to the pressure value of the standard fuel, and when the valve closing timing has reached the most retarded angle, the controller may correct the intake valve closing timing so that the higher the measured pressure value is relative to the pressure value of the standard fuel, the less fuel is injected.

[0032] The higher the measured pressure value is relative to the pressure value of the standard fuel, the more the intake valve closing timing is retarded, thereby adjusting the temperature inside the cylinder according to the properties of the fuel (i.e., the temperature inside the cylinder decreases). However, once the intake valve closing timing reaches its maximum retardation, further retarding the intake valve closing timing does not reduce the temperature inside the cylinder any further. The controller does not retard the intake valve closing timing beyond its maximum retardation. Instead, the controller reduces the amount of fuel injected. This reduces the amount of heat generated, making combustion equivalent to that of standard fuel.

[0033] The technology disclosed herein relates to an engine system. a controller storing information about the properties of a standard fuel; In response to the control signal from the controller ,workman an injector that injects fuel into a cylinder of the engine; an in-cylinder pressure sensor attached to the engine and outputting a pressure signal corresponding to the pressure in the cylinder to the controller; a crank angle sensor attached to the engine and outputting a crank angle signal corresponding to a crank angle of the engine to the controller; the controller causes the injector to perform a fuel injection for determination at a specific time point after an intake valve of the cylinder is closed during motoring of the engine; The controller performs the above-described operation based on the crank angle signal of the crank angle sensor and the pressure signal of the in-cylinder pressure sensor. The injector is used for judgment. fuel into the cylinder injection did a pressure value in the cylinder at a time when a specific crank angle period has elapsed since the time point; the information stored in the controller is a pressure value in the cylinder at a time when the specific crank angle period has elapsed after the standard fuel is injected into the cylinder at the specific time point; The controller determines the properties of the fuel injected by the injector based on a comparison between the pressure value of the standard fuel and the acquired pressure value.

[0034] With this configuration, the controller can accurately determine the properties of the fuel supplied to the engine while the engine is motoring. [Effects of the Invention]

[0035] The engine control method and engine system described above can accurately determine the properties of the fuel supplied to the engine. [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 illustrates an engine system. [Figure 2] FIG. 2 illustrates an engine system. [Figure 3] FIG. 3 illustrates the difference in pressure change inside the cylinder when a plurality of fuels with different properties are injected. [Figure 4] FIG. 4 illustrates the relationship between the progression of the cycle and the first period of pressure values. [Figure 5] FIG. 5 shows an example of a correction map for the fuel injection amount and the intake valve closing timing. [Figure 6] FIG. 6 illustrates the control flow of the engine system executed by the controller. DETAILED DESCRIPTION OF THE INVENTION

[0037] Hereinafter, an embodiment of an engine control method and an engine system will be described with reference to the drawings. The control method and engine system described here are exemplary.

[0038] FIG. 1 is a diagram illustrating an engine system 1. The engine system 1 is mounted on a four-wheeled automobile. The engine system 1 includes an engine 100 and a controller that controls the engine 100. The controller is an ECU (Engine Control Unit) 10, which will be described later. FIG. 2 is a block diagram showing a configuration related to the control of the engine system 1.

[0039] The engine 100 has a cylinder 11. An intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke are repeated in the cylinder 11. The engine 100 is a four-stroke engine. The automobile travels when the engine 100 is operated. The fuel for the engine 100 is gasoline in this configuration example. The engine 100 may be configured so that the air-fuel mixture burns by self-ignition in at least a part of the operating range. The fuel for the engine 100 may also be diesel fuel.

[0040] (Engine configuration) The engine 100 includes a cylinder block 12 and a cylinder head 13. A plurality of cylinders 11 are formed in the cylinder block 12. The engine 100 is a multi-cylinder engine. Only one cylinder 11 is shown in FIG. 1.

[0041] A piston 3 is inserted into each cylinder 11. The piston 3 is connected to a crankshaft 15 via a connecting rod 14. The piston 3, the cylinder 11, and the cylinder head 13 form a combustion chamber 17.

[0042] The geometric compression ratio of the engine system 1 is set high in order to improve theoretical thermal efficiency. Specifically, the geometric compression ratio ε of the engine system 1 is 14.0 or more. The geometric compression ratio may be, for example, 18. The geometric compression ratio may be set appropriately within the range of 14 to 20.

[0043] An intake port 18 is formed in the cylinder head 13 for each cylinder 11. The intake port 18 communicates with the interior of the cylinder 11.

[0044] An intake valve 21 is disposed in the intake port 18. The intake valve 21 opens and closes the intake port 18. The intake valve 21 is a poppet valve. The valve train has an intake camshaft and is mechanically connected to the intake valve 21. The valve train opens and closes the intake valve 21 at a predetermined timing. The valve train is a variable valve train that varies the valve timing and / or valve lift. As shown in FIG. 2, the valve train has an intake S-VT (Sequential-Valve Timing) 23. The intake S-VT 23 continuously changes the rotational phase of the intake camshaft relative to the crankshaft 15 within a predetermined angle range. The opening period of the intake valve 21 does not change. The intake S-VT 23 is a variable phase mechanism. The intake S-VT 23 is an electric or hydraulic type.

[0045] An exhaust port 19 is formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 communicates with the interior of the cylinder 11.

[0046] An exhaust valve 22 is disposed in the exhaust port 19. The exhaust valve 22 opens and closes the exhaust port 19. The exhaust valve 22 is a poppet valve. The valve train has an exhaust camshaft and is mechanically connected to the exhaust valve 22. The valve train opens and closes the exhaust valve 22 at a predetermined timing. The valve train is a variable valve train that varies the valve timing and / or the valve lift. As shown in FIG. 2, the valve train has an exhaust S-VT 24. The exhaust S-VT 24 continuously changes the rotational phase of the exhaust camshaft relative to the crankshaft 15 within a predetermined angle range. The opening period of the exhaust valve 22 does not change. The exhaust S-VT 24 is a variable phase mechanism. The exhaust S-VT 24 is of an electric or hydraulic type.

[0047] An injector 6 is attached to the cylinder head 13 for each cylinder 11. The injector 6 injects fuel directly into the cylinder 11.

[0048] A fuel supply system 61 is connected to the injector 6. The fuel supply system 61 includes a fuel tank 63 configured to store fuel, and a fuel supply passage 62 that connects the fuel tank 63 and the injector 6 to each other. A fuel pump 65 and a common rail 64 are disposed in the fuel supply passage 62. The fuel pump 65 pumps fuel to the common rail 64. The common rail 64 stores the fuel pumped from the fuel pump 65 at high fuel pressure. When the injector 6 opens, the fuel stored in the common rail 64 is injected into the cylinder 11 from the nozzle of the injector 6. The configuration of the fuel supply system 61 is not limited to the above configuration.

[0049] A spark plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the air-fuel mixture in the cylinder 11.

[0050] An intake passage 40 is connected to one side of the engine 100. The intake passage 40 is connected to the intake ports 18 of each cylinder 11. Air introduced into the cylinders 11 flows through the intake passage 40. An air cleaner 41 is disposed at the upstream end of the intake passage 40. The air cleaner 41 filters the air. A surge tank 42 is disposed near the downstream end of the intake passage 40. The portion of the intake passage 40 downstream of the surge tank 42 forms an independent intake passage that branches off for each cylinder 11. The downstream end of the independent intake passage is connected to the intake port 18 of each cylinder 11.

[0051] A throttle valve 43 is disposed between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 adjusts the amount of air introduced into the cylinder 11 by adjusting the opening of the valve.

[0052] An exhaust passage 50 is connected to the other side of the engine 100. The exhaust passage 50 communicates with the exhaust ports 19 of each cylinder 11. The exhaust passage 50 is a passage through which exhaust gas discharged from the cylinder 11 flows. Although not shown in detail, the upstream portion of the exhaust passage 50 forms an independent exhaust passage that branches off for each cylinder 11. The upstream end of the independent exhaust passage is connected to the exhaust port 19 of each cylinder 11.

[0053] An exhaust gas purification system having multiple catalytic converters is arranged in the exhaust passage 50. The upstream catalytic converter has, for example, a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter has a three-way catalyst 513. Note that the exhaust gas purification system is not limited to the configuration shown in the illustration. For example, the GPF may be omitted. Furthermore, the catalytic converter is not limited to one having a three-way catalyst. Furthermore, the order of the three-way catalyst and the GPF may be changed as appropriate.

[0054] An EGR passage 52 is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for recirculating a portion of the exhaust gas back into the intake passage 40. The upstream end of the EGR passage 52 is connected between the upstream catalytic converter and the downstream catalytic converter in the exhaust passage 50. The downstream end of the EGR passage 52 is connected between the throttle valve 43 and the surge tank 42 in the intake passage 40.

[0055] A water-cooled EGR cooler 53 is disposed in the EGR passage 52. The EGR cooler 53 cools the exhaust gas. An EGR valve 54 is also disposed in the EGR passage 52. The EGR valve 54 adjusts the flow rate of the exhaust gas flowing through the EGR passage 52. When the opening of the EGR valve 54 is adjusted, the amount of recirculated EGR gas from the outside is adjusted.

[0056] As shown in Fig. 2, the engine system 1 includes an ECU (Engine Control Unit) 10 for operating an engine 100. The ECU 10 is a controller based on a well-known microcomputer. The ECU 10 includes a central processing unit (CPU) 101 that executes programs, a memory 102 configured, for example, by a RAM (Random Access Memory) or a ROM (Read Only Memory) that stores programs and data, and an I / F circuit 103 that inputs and outputs electrical signals. The ECU 10 is an example of a controller.

[0057] 1 and 2, various sensors SW1 to SW9 are connected to the ECU 10. The sensors SW1 to SW9 output signals to the ECU 10. The sensors include the following sensors. Air flow sensor SW1: disposed downstream of the air cleaner 41 in the intake passage 40, and measures the flow rate of air flowing through the intake passage 40. Intake air temperature sensor SW2: disposed downstream of the air cleaner 41 in the intake passage 40, and measures the temperature of the air flowing through the intake passage 40. Intake pressure sensor SW3: attached to the surge tank 42 and measures the pressure of the air introduced into the cylinder 11. · Cylinder pressure sensor SW4: attached to the cylinder head 13 corresponding to each cylinder 11, and measures the pressure inside each cylinder 11. Water temperature sensor SW5: attached to the engine 100 and measures the temperature of the cooling water. Crank angle sensor SW6: attached to the engine 100 and measures the rotation angle of the crankshaft 15. · Accelerator opening sensor SW7: Attached to the accelerator pedal mechanism, it measures the accelerator opening corresponding to the amount of accelerator pedal operation. Intake cam angle sensor SW8: attached to the engine 100 and measures the rotation angle of the intake camshaft. Exhaust cam angle sensor SW9: attached to the engine 100 and measures the rotation angle of the exhaust camshaft.

[0058] The ECU 10 determines the operating state of the engine 100 based on the signals from these sensors SW1 to SW9, and calculates the control amount of each device according to a predetermined control logic. The control logic is stored in the memory 102. The control logic includes calculating the target amount and / or the control amount using a map stored in the memory 102.

[0059] The ECU 10 outputs electrical signals related to the calculated control amounts to the injector 6, the spark plug 25, the intake S-VT 23, the exhaust S-VT 24, the fuel supply system 61, the throttle valve 43, and the EGR valve .

[0060] The engine 100 also includes a starter 7. The starter 7 is connected to the crankshaft 15 of the engine 100. The starter 7 is an electric motor. When the driver turns on the ignition switch, the ECU 10 outputs an electric signal to the starter 7. The starter 7 is turned on and the crankshaft 15 rotates. Motoring of the engine 100 begins. After motoring begins, the ECU 10 outputs an electric signal to the injector 6 and the spark plug 25, thereby completing the starting of the engine 100.

[0061] (Determination of fuel properties) The properties of the fuel supplied to the fuel tank 63 are not always the same. The properties of the fuel supplied to the fuel tank 63 may be significantly different from those of standard fuel.

[0062] The memory 102 of the ECU 10 stores a map that is set based on the properties of standard fuel. The ECU 10 uses the map based on the standard fuel to control the engine 100. If the properties of the fuel supplied to the engine 100 change from the properties of the standard fuel, misfires or sudden combustion may occur.

[0063] Therefore, the engine system 1 determines the properties of the fuel supplied to the engine 100. The engine system 1 also corrects the control amount of the engine 100 according to the determined properties of the fuel.

[0064] First, a method for determining fuel properties will be described with reference to the drawings. The ECU 10 determines fuel properties while the engine 100 is motoring. Motoring of the engine 100 refers to a state in which the starter 7 rotates the crankshaft 15 and no high-temperature oxidation reaction occurs within the cylinders 11. While the engine 100 is motoring, no heat is generated within the cylinders 11 due to a fuel reaction, and no residual combustion gas is generated. Therefore, the ECU 10 can determine the fuel properties without being affected by these factors. This improves the accuracy of the determination.

[0065] Figure 3 illustrates an example of changes in pressure within a certain cylinder 11 while the engine 100 is motoring. The horizontal axis of Figure 3 represents the progression of the crank angle, and the vertical axis represents the pressure within the cylinder 11. As shown by the solid line, after the intake valve 21 closes (i.e., IVC), the pressure within the cylinder 11 begins to rise as the piston 3 rises.

[0066] The ECU 10 causes the injector 6 to inject fuel for determination into the cylinder 11 at a specific time point after the IVC. The cylinder 11 into which fuel is injected may be the cylinder 11 whose intake valve 21 closes first after the crankshaft 15 starts rotating.

[0067] As the engine 100 cycles one, two, and so on, the temperature inside the cylinder 11 gradually rises. As the temperature inside the cylinder 11 rises, the heat may affect the determination of the fuel properties. By using the cylinder 11 whose intake valve 21 is closed first, the ECU 10 can determine the fuel properties without being affected by the heat. This improves the accuracy of determining the fuel properties.

[0068] Here, the injector 6 may inject a small amount of fuel into the cylinder 11 as the fuel for determination, the amount of fuel being small enough not to cause a high-temperature oxidation reaction.

[0069] The fuel injected into the cylinder 11 undergoes a low-temperature oxidation reaction over time as the pressure in the cylinder 11 gradually increases as the piston 3 rises, and the fuel breaks up, atomizes, evaporates, and mixes with air.

[0070] Here, the amount of heat generated varies depending on the fuel's properties, such as its specific heat ratio and / or gas constant. In other words, the amount of heat generated varies because the initial chemical reaction in the preparation stage for the low-temperature oxidation reaction (e.g., when the in-cylinder gas temperature is 700 K) differs. The initial chemical reaction is the generation of radicals (alkyl peroxides (RO2, QOOHO2)) through a hydrogen abstraction reaction. The difference in the amount of heat generated changes the rate of pressure increase in the cylinder 11. The dashed line in Figure 3 illustrates the pressure increase when a standard fuel is injected into the cylinder 11. With the standard fuel, the pressure in the cylinder 11 reaches the reference pressure Px after a first period t1 has elapsed since the time of fuel injection. The first period t1 corresponds to a "specific crank angle period."

[0071] The first period t1 corresponds to the period during which the fuel injected from the injector 6 into the cylinder 11 undergoes splitting, atomization, evaporation, and mixing with air, leading to a low-temperature oxidation reaction. The pressure inside the cylinder 11 at the end of the first period t1 reflects the amount of heat generated in the initial chemical reaction of the fuel. The first period t1 may be the period before the piston 3 in the cylinder 11 reaches top dead center (TDC) of compression.

[0072] When a different fuel with different properties than the standard fuel is injected into the cylinder 11, the rate of pressure rise in the cylinder 11 changes due to the difference in the amount of heat generated. The dotted line in FIG. 3 illustrates the pressure rise when a different fuel that generates heat more easily than the standard fuel is injected into the cylinder 11. Because the different fuel is a fuel that is more susceptible to low-temperature oxidation reactions, the pressure rise in the cylinder 11 is promoted. The pressure in the cylinder 11 after the first period t1 has elapsed is higher than the pressure of the standard fuel (measured pressure P1). The dashed-dotted line in FIG. 3 illustrates the pressure rise when a different fuel that generates heat less easily than the standard fuel is injected into the cylinder 11. Because the different fuel is a fuel that is less susceptible to low-temperature oxidation reactions, the pressure rise in the cylinder 11 is suppressed. The pressure in the cylinder 11 after the first period t1 has elapsed is lower than the pressure of the standard fuel (measured pressure P2).

[0073] The memory 102 stores information about the properties of the standard fuel. More specifically, the information is the pressure value (i.e., reference pressure Px) in the cylinder 11 at a specific crank angle period (i.e., first period t1) after the standard fuel is injected into the cylinder 11 at a specific time point.

[0074] The ECU 10 acquires the pressure value inside the cylinder 11 at the time when the first period t1 has elapsed after the injector 6 has injected the fuel for evaluation from the measurement signal of the in-cylinder pressure sensor SW4, and compares the measured pressure P with the reference pressure Px stored in the memory 102. If the measured pressure P and the reference pressure Px match, the ECU 10 can determine that the properties of the fuel injected by the injector 6 match the properties of the standard fuel. If the measured pressure P is higher than the reference pressure Px, the ECU 10 can determine that the fuel injected by the injector 6 is a fuel that generates heat more easily than the standard fuel. If the measured pressure P is lower than the reference pressure Px, the ECU 10 can determine that the fuel injected by the injector 6 is a fuel that generates heat less easily than the standard fuel.

[0075] Here, the ECU 10 may determine the fuel properties based only on the pressure value P measured in the cylinder 11 whose intake valve 21 closes first after the crankshaft 15 starts rotating. Alternatively, the ECU 10 may measure the pressure value P not only in the cylinder 11 whose intake valve 21 closes first, but also in each of the multiple cylinders 11 that subsequently enter the compression stroke, and determine the fuel properties based on the average value of the multiple pressure values ​​P. The ECU 10 may measure pressure values ​​P for, for example, 4 to 5 cycles.

[0076] When the pressure value P is measured in each of the multiple cylinders 11, as the cycle of the engine 100 progresses during motoring, the piston speed increases, and the temperature inside the cylinder 11 also increases. When the temperature inside the cylinder 11 increases, the reaction speed of the fuel injected into the cylinder 11 changes, and the pressure after the first period t1 is affected by the temperature change inside the cylinder 11.

[0077] Therefore, the ECU 10 may change the length of the first period t1 according to the progress of the cycle of the engine 100. Figure 4 illustrates an example of the relationship between the progress of the cycle of the engine 100 and the length of the first period t1. As the cycle of the engine 100 progresses from the first cycle to the second cycle, the third cycle, and the fourth cycle, the length of the first period t1 gradually shortens. This eliminates the influence of the gradually increasing temperature inside the cylinder 11, and allows the ECU 10 to determine differences in the pressure increase inside the cylinder 11 that are caused only by the properties of the fuel.

[0078] (Engine control according to fuel properties) After the engine 100 has started, the ECU 10 operates the engine 100 while correcting the fuel injection amount and / or the intake valve closing timing (IVC) of the intake valve 21 according to the determined fuel properties. This makes it possible to make combustion equivalent to that of a standard fuel even if the combustion properties are different, which is advantageous for improving the fuel economy and exhaust gas performance of the engine 100. It also makes it possible to suppress an increase in combustion noise.

[0079] 5 shows an example of a fuel injection amount correction map (upper diagram) and a valve closing timing correction map (lower diagram). These correction maps are stored in the memory 102 of the ECU 10. In each correction map, the horizontal axis represents the measured pressure minus the reference pressure, with the left side of the diagram (i.e., negative) indicating that the measured pressure P is lower than the reference pressure Px, and the right side of the diagram (i.e., positive) indicating that the measured pressure P is higher than the reference pressure Px.

[0080] If the measured pressure P is higher than the reference pressure Px, the fuel is relatively prone to heat generation. Therefore, as shown in the lower diagram of Figure 5, the ECU 10 corrects the closing timing of the intake valve 21 to the retard side via the intake S-VT 23. When the closing timing of the intake valve 21 is retarded, the temperature inside the cylinder 11 drops, making the fuel less likely to generate heat. Even if the fuel is prone to heat generation, combustion will be equivalent to combustion of standard fuel. Note that the closing timing of the intake valve 21 is set to be after the intake bottom dead center.

[0081] Conversely, if the measured pressure P is lower than the reference pressure Px, the fuel is relatively less likely to generate heat. Therefore, as shown in the lower diagram of Figure 5, the ECU 10 corrects the closing timing of the intake valve 21 to the advanced side via the intake S-VT 23. When the closing timing of the intake valve 21 is advanced, the temperature inside the cylinder 11 increases, making the fuel more likely to generate heat. Even if the fuel is less likely to generate heat, combustion will be equivalent to combustion of standard fuel.

[0082] 5, the higher the measured pressure P is relative to the reference pressure Px, the more the closing timing of the intake valve 21 is corrected to be retarded, and the lower the measured pressure P is relative to the reference pressure Px, the more the closing timing of the intake valve 21 is corrected to be advanced. This allows the temperature inside the cylinder 11 to be adjusted to a temperature according to the properties of the fuel.

[0083] However, there is a limit to the amount by which the closing timing of the intake valve 21 can be retarded, and even if the closing timing of the intake valve 21 is retarded beyond the maximum retardation amount, the temperature inside the cylinder 11 is unlikely to drop any further. Therefore, when the closing timing reaches the maximum retardation in the control map shown in the lower diagram of Figure 5, the ECU 10 corrects the fuel injection amount so that the higher the measured pressure P is relative to the reference pressure Px, as shown in the upper diagram of Figure 5. Because the reduction in the fuel injection amount reduces the amount of heat generated, combustion becomes equivalent to combustion of standard fuel.

[0084] (Control Flow) Next, the control procedure executed by the ECU 10 will be described with reference to the flow of Fig. 6. First, in step S1 after starting, the ECU 10 determines whether or not it is time to start the engine 100. If it is not time to start, the process repeats step S1, and if it is time to start, the process proceeds to step S2.

[0085] In step S2, the ECU 10 determines whether or not it is the first cycle since the crankshaft 15 starts to rotate. If it is the first cycle, the process proceeds to step S3, and if it is the second or subsequent cycle, the process proceeds to step S11.

[0086] In step S3, the ECU 10 determines whether the intake valve 21 in the cylinder 11 into which the fuel for determination is to be injected has closed. Note that in the first cycle, this is the intake valve 21 that closes first after the crankshaft 15 starts rotating. If the determination in step S3 is NO, the process repeats step S3, and if the determination in step S3 is YES, the process proceeds to step S4.

[0087] In step S4, the ECU 10 causes the injector 6 to inject fuel for determination at a specific time point after the intake valve 21 closes, and then in the following step S5, the ECU 10 acquires the pressure inside the cylinder 11 at the time when the first period t1 has elapsed from the time of fuel injection based on the measurement signals of the in-cylinder pressure sensor SW4 and the crank angle sensor SW6.

[0088] In step S6, the ECU 10 determines whether a predetermined number of cycles has elapsed since the start of motoring of the engine 10. This predetermined number of cycles is the number of cycles for which pressure measurement is performed, and may be, for example, 4 to 5 cycles. If the determination in step S6 is NO, the process returns to step S2.

[0089] In step S2, if it is the second or subsequent cycle, the process proceeds to step S11. After the ECU 10 changes the first period t1 according to the map in Fig. 4, the ECU 10 executes steps S3 to S5. In this way, fuel injection into the cylinder 11 and pressure measurement are repeated multiple times.

[0090] If the determination in step S6 is YES, the process proceeds to step S7. ECU 10 calculates the average value of the measured pressure values, and then in step S8, calculates the difference between the measured pressure and a reference pressure for a standard fuel. Then, in step S9, ECU 10 determines whether there is a discrepancy between the measured pressure and the reference pressure. If there is a discrepancy, the process proceeds to step S10. In step S10, ECU 10 corrects the fuel injection amount and / or the closing timing of intake valve 21 after engine 100 has finished starting in accordance with the properties of the fuel, in accordance with the control map in FIG. 5. On the other hand, if there is no discrepancy, ECU 10 does not correct the fuel injection amount or the closing timing of intake valve 21.

[0091] According to the control method for engine 100 and engine system 1 disclosed herein, while engine 100 is motoring, fuel for determination is injected into cylinder 11 during the compression stroke, allowing EUC 10 to accurately determine the properties of the fuel.

[0092] Furthermore, by correcting the control amount of the engine 100 in accordance with the determined fuel properties, combustion during operation of the engine 100 becomes equivalent to combustion of standard fuel, thereby improving fuel economy and exhaust gas performance. In addition, an increase in combustion noise can be suppressed.

[0093] The technology disclosed herein is not limited to application to the engine system 1 having the above-described configuration. The technology disclosed herein can be applied to engine systems 1 having various configurations. For example, the technology disclosed herein can also be applied to a diesel engine.

[0094] The technology disclosed herein can also be applied to so-called hybrid vehicles. In this case, motoring of the engine may be performed by a generator. In addition, in hybrid vehicles, the engine may be started in response to a request for power generation or torque. The ECU 10 may determine the properties of the fuel when the engine is started in response to a request for power generation or torque. [Explanation of symbols]

[0095] 1 Engine System 10 ECU (controller) 100 Engine 11 cylinders 15 crankshaft 21 Intake valve 6 injectors SW4 Cylinder pressure sensor SW6 crank angle sensor

Claims

1. A method for controlling an engine having a plurality of cylinders, wherein an injector injects fuel for determination into a cylinder of the engine at a specific time after an intake valve of the cylinder closes, during motoring of the engine, comprising: the injector injects fuel for determination into a cylinder whose intake valve is first closed after the crankshaft of the engine starts to rotate, The injector also injects fuel for determination into each of a plurality of cylinders as the engine cycle progresses; an in-cylinder pressure sensor outputs to a controller a signal corresponding to the pressure in the plurality of cylinders at least at a time when a specific crank angle period has elapsed since the injector injected the fuel for determination into the cylinder; the controller determines the properties of the fuel injected by the injector by comparing an average value of the pressure values ​​for each of the plurality of cylinders measured by the in-cylinder pressure sensor with a pre-stored pressure value, which is a pressure value in the cylinder at a time point when the specific crank angle period has elapsed after the standard fuel is injected into the cylinder at the specific time point; The specific crank angle period becomes shorter with each progression of the cycle. How to control the engine.

2. 2. The engine control method according to claim 1, The engine control method, wherein the specific crank angle period corresponds to a period during which fuel injected from the injector into the cylinder undergoes fragmentation, atomization, evaporation, and mixing with air, leading to a low-temperature oxidation reaction.

3. 3. The engine control method according to claim 1 or 2, The engine control method includes correcting at least one of a fuel injection amount and a closing timing of the intake valve according to a property of the fuel after the engine has been started.

4. 4. The engine control method according to claim 3, the controller corrects the closing timing of the intake valve to the retard side when the measured pressure value is higher than the pressure value of the standard fuel, and corrects the closing timing of the intake valve to the advance side when the measured pressure value is lower than the pressure value of the standard fuel.

5. 5. The engine control method according to claim 4, the controller corrects the intake valve closing timing so as to be more retarded the higher the measured pressure value is relative to the pressure value of the standard fuel, and when the valve closing timing has reached its most retarded position, the controller corrects the intake valve closing timing so as to be more retarded the higher the measured pressure value is relative to the pressure value of the standard fuel, thereby reducing the fuel injection amount.

6. a controller storing information about the properties of a standard fuel; an injector that injects fuel into a cylinder of the engine in response to a control signal from the controller; an in-cylinder pressure sensor attached to the engine and outputting a pressure signal corresponding to the pressure in the cylinder to the controller; a crank angle sensor attached to the engine and outputting a crank angle signal corresponding to a crank angle of the engine to the controller; the controller causes the injector to perform a fuel injection for determination at a specific time point after an intake valve of the cylinder is closed during motoring of the engine; the controller acquires a pressure value in the cylinder at a time when a specific crank angle period has elapsed since the injector injected fuel for determination into the cylinder, based on a crank angle signal from the crank angle sensor and a pressure signal from the in-cylinder pressure sensor; the information stored in the controller is a pressure value in the cylinder at a time when the specific crank angle period has elapsed after the standard fuel is injected into the cylinder at the specific time point; The controller determines the properties of the fuel injected by the injector based on a comparison between the pressure value of the standard fuel and the acquired pressure value.

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