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, a cylinder inner pressure sensor SW4 outputs to a controller (ECU 10) a signal of reference pressure indicating pressure change in a cylinder after an intake valve 21 of the cylinder of the engine is closed, the pressure change caused in the case where fuel injection is not performed, and during motoring, an injector 6 injects fuel for determination into the cylinder 11 at a specific time point after closing of the intake valve 21. The controller acquires a crank angle period from valve opening timing of the intake valve through fuel injection to a time point at which pressure in the cylinder reaches reference pressure. The controller determines properties of the fuel injected by the injector by comparing a crank angle period of standard fuel with the acquired crank angle period, based on information on stored properties of the standard fuel.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 in-cylinder pressure sensor outputs a reference pressure signal to a controller, the reference pressure signal being a pressure change in the cylinder of the engine after an intake valve of the cylinder is closed and in the case where no fuel injection is performed; During motoring of the engine after the reference pressure is output, an injector injects fuel for determination into the cylinder at a specific time point after the intake valve closes, the controller acquires a crank angle period from the intake valve closing timing, through the fuel injection, to the time when the pressure in the cylinder reaches the reference pressure, based on a signal from the in-cylinder pressure sensor and a signal from the crank angle sensor; The controller determines the properties of the fuel injected by the injector by comparing the crank angle period from the intake valve closing timing based on stored information about the properties of the standard fuel to the time when the standard fuel is injected into the cylinder at the specific time point and the pressure in the cylinder reaches the reference pressure with the acquired crank angle period.

[0008] According to this configuration, the in-cylinder pressure sensor measures changes in pressure within 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 start of the engine. In an internal combustion engine vehicle, the start of the engine corresponds to the moment when the occupant turns on the ignition switch of the vehicle, or in a hybrid vehicle, the moment 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 cylinder pressure sensor measures the pressure change during the compression stroke after the intake valve closes. This pressure change is the pressure change when only the air in the cylinder is compressed. This pressure change becomes the reference pressure.

[0010] Once the reference pressure is measured, the injector injects fuel into the next cylinder while the engine is motoring. Specifically, the fuel for determination is injected into the cylinder at a specific point in 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 the compression stroke. The "fuel for determination" is fuel that is supplied into the cylinder to determine the fuel properties.

[0011] When fuel is injected into a cylinder during the compression stroke, when the temperature and pressure inside the cylinder are gradually increasing, the temperature and pressure inside the cylinder temporarily drop below the reference pressure due to the latent heat of vaporization of the fuel. As the compression stroke progresses, the fuel undergoes fragmentation, atomization, evaporation, and mixing with air over time, resulting in a low-temperature oxidation reaction. During this time, the pressure inside the cylinder returns to the reference pressure. Different fuel properties, such as the boiling point and / or latent heat of vaporization, affect the time it takes for the fuel to evaporate after being injected into the cylinder. This causes a difference in the time it takes for the pressure inside the cylinder to return to the reference pressure after dropping below the reference pressure.

[0012] The controller acquires the crank angle period from the intake valve closing timing, through fuel injection, to the time when the pressure in the cylinder reaches a reference pressure, based on the signals from the in-cylinder pressure sensor and the crank angle sensor. If the fuel injected by the injector has a low boiling point and is easily evaporated, the crank angle period is relatively short, and if the fuel has a high boiling point and is not easily heated, the crank angle period is relatively long.

[0013] The controller stores information about the properties of a standard fuel. A "standard fuel" is, for example, a fuel that corresponds to K2202 (gasoline for automobiles) or K2204 (diesel for automobiles) as specified in the JIS standard. Based on the information about the properties of the standard fuel, the controller can determine the crank angle period from the intake valve closing time until the standard fuel is injected into the cylinder at a specific time and the pressure inside the cylinder reaches a reference pressure. The controller also compares the measured crank angle period with the crank angle period of the standard fuel.

[0014] Specifically, if the measured crank angle period is shorter than the crank angle period for standard fuel, the fuel injected by the injector has a low boiling point and is easily evaporated. Therefore, when the engine is running after starting, that is, when the engine is operating by burning the fuel injected into the cylinders, unlike motoring, fuel premixing is likely to occur. Therefore, in a lean mixture, low-temperature oxidation reactions are difficult, and subsequent high-temperature oxidation reactions are also difficult, making ignition difficult. As a result, combustion becomes slow, which may lead to reduced fuel economy and torque. On the other hand, in a rich mixture, the mixture ignites and burns all at once, which may increase combustion noise.

[0015] On the other hand, if the measured crank angle period is longer than the crank angle period for the standard fuel, the fuel injected by the injector has a high boiling point and is difficult to evaporate. Therefore, when the engine is running after starting, it is difficult for the fuel to be premixed, which makes it more likely to undergo diffusion combustion. In this case, the combustion may become too rapid, increasing combustion noise and increasing soot in the fuel-rich parts of the mixture.

[0016] This technology takes advantage of the fact that the boiling point and / or latent heat of vaporization differ depending on the fuel. The evaporation characteristics of the fuel inside the cylinder change depending on the boiling point and / or latent heat of vaporization of the fuel injected into the cylinder. Based on this, the controller compares the crank angle period from the intake valve closing time, through fuel injection, to the time when the pressure inside the cylinder reaches a reference pressure. This allows the controller to accurately determine the properties of the fuel supplied to the engine.

[0017] 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.

[0018] the engine has a plurality of cylinders; The cylinder pressure sensor may output a signal of a reference pressure in a cylinder whose intake valve closes first after a crankshaft of the engine starts to rotate.

[0019] This allows the in-cylinder pressure sensor to measure the reference pressure when the air in the cylinder is compressed without being affected by heat or residual gas. Also, as the engine cycle progresses, the crankshaft rotation speed gradually increases, causing the temperature in the cylinder to gradually rise. By measuring the reference pressure in the cylinder where the intake valve first closes after the engine crankshaft starts rotating, the in-cylinder pressure sensor can accurately measure the reference pressure.

[0020] The injector injects fuel for determination into each of a plurality of cylinders as the engine cycle progresses, the controller obtains a crank angle period for each of the plurality of cylinders; The controller may compare an average value of a plurality of crank angle periods to the crank angle period of the standard fuel.

[0021] The controller can improve the accuracy of the determination by determining the fuel properties using an average value over multiple crank angle periods.

[0022] The crank angle duration of the standard fuel may be shortened with each progression of the cycle.

[0023] As described above, the temperature inside the cylinder gradually increases as the engine cycle progresses. The increase in temperature inside the cylinder promotes evaporation of the fuel injected into the cylinder and shortens the crank angle period required to reach the reference pressure. As the crank angle period for the standard fuel shortens with each cycle, it is possible to measure the crank angle period without the influence of temperature increases in each of the multiple cycles. The controller can more accurately determine the properties of the fuel based on the multiple crank angle periods.

[0024] The controller may correct at least one of a fuel injection start timing and a closing timing of the intake valve according to the properties of the fuel after the engine has been started.

[0025] If the fuel injected by the injector is easily vaporized, it may result in a decrease in fuel economy or an increase in combustion noise, as described above. If the fuel is not easily vaporized, it may result in a decrease in exhaust gas emissions or an increase in combustion noise, as described above.

[0026] The controller corrects at least one of the fuel injection start timing 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.

[0027] The controller may correct the start timing of fuel injection to the advance side when the acquired crank angle period is longer than the crank angle period of the standard fuel, and correct the start timing of fuel injection to the retard side when the acquired crank angle period is shorter than the crank angle period of the standard fuel.

[0028] If the acquired crank angle period is longer than the crank angle period of the standard fuel, the fuel is relatively less likely to evaporate. Therefore, the start timing of fuel injection is corrected to the advance side. If the start timing of fuel injection is advanced, time for the fuel to evaporate is ensured. Even if the fuel is less likely to evaporate, the fuel evaporates at the desired timing, so combustion is equivalent to combustion of the standard fuel. Conversely, if the acquired crank angle period is shorter than the crank angle period of the standard fuel, the fuel is relatively more likely to evaporate. Therefore, the start timing of fuel injection is corrected to the retard side. If the start timing of fuel injection is delayed, the timing at which fuel evaporation is completed is delayed, so the fuel evaporates at the desired timing. Even if the fuel is more likely to evaporate, combustion is equivalent to combustion of the standard fuel.

[0029] The controller corrects the start timing of the fuel injection so that the longer the acquired crank angle period is with respect to the crank angle period of the standard fuel, the more advanced the start timing of the fuel injection is. Start of When the timing reaches a first timing on the advance side, the longer the acquired crank angle period is with respect to the crank angle period of the standard fuel, the more the intake valve closing timing may be advanced.

[0030] Advancing the fuel injection start timing increases the time for fuel to evaporate. However, advancing the fuel injection start timing shortens the period between the intake valve closing timing and the fuel injection start timing, resulting in a lower pressure inside the cylinder at the start of fuel injection. If the pressure inside the cylinder is too low, the pressure difference between the fuel injection pressure and the pressure inside the cylinder increases, increasing the penetration of the fuel spray. As a result, the injected fuel adheres to the cylinder surface, preventing the fuel from evaporating. The controller does not advance the fuel injection start timing beyond the first time. Instead, the controller advances the intake valve closing timing. This increases the temperature and pressure inside the cylinder, making it easier for the fuel to evaporate inside the cylinder. As a result, when the fuel is not easily evaporated, combustion becomes equivalent to that of standard fuel.

[0031] The controller corrects the start timing of the fuel injection so that the shorter the acquired crank angle period is with respect to the crank angle period of the standard fuel, the more delayed the start timing of the fuel injection is. Start of When the timing reaches a second period on the retard side, the shorter the acquired crank angle period is with respect to the crank angle period of the standard fuel, the more the intake valve closing timing may be retarded.

[0032] Retarding the start of fuel injection shortens the time for fuel to evaporate. However, when the start of fuel injection is retarded, the end of fuel injection approaches the top dead center of compression, meaning that the evaporation time of fuel injected later is too short. This can easily lead to soot formation. The controller does not retard the start of fuel injection beyond the second time. Instead, the controller retards the closing timing of the intake valve. This reduces the temperature and pressure inside the cylinder, slowing the evaporation of the fuel. As a result, when the fuel is prone to evaporation, combustion is 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 in-cylinder pressure sensor outputs a reference pressure signal that indicates a pressure change after an intake valve of a cylinder of the engine is closed during motoring of the engine, the reference pressure signal corresponding to the pressure in the cylinder when no fuel injection is performed; the controller causes the injector to perform a fuel injection for determination at a specific time point after the intake valve closes during motoring of the engine after the reference pressure is output; the controller acquires a crank angle period from the intake valve closing timing, through the fuel injection, to the time when the pressure in the cylinder reaches the reference pressure, based on the crank angle signal of the crank angle sensor and the pressure signal of the cylinder internal pressure sensor; The controller determines the properties of the fuel injected by the injector by comparing the crank angle period from the intake valve closing timing to the time when the standard fuel is injected into the cylinder at the specific time point and the pressure in the cylinder reaches the reference pressure, based on stored information about the properties of the standard fuel, with the acquired crank angle period.

[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 reference period. [Figure 5] FIG. 5 shows an example of a correction map for the fuel injection start timing 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 measures the pressure change in the cylinder 11 due to air compression based on the signal from the in-cylinder pressure sensor SW4 for the cylinder 11 whose intake valve 21 closes first after the crankshaft 15 starts rotating. This is the "air compression pressure" in Figure 3, and this air compression pressure corresponds to the reference pressure.

[0067] As the engine 100 cycles one, two, and so on, the temperature inside the cylinder 11 gradually rises. By measuring the reference pressure in the cylinder 11 where the intake valve 21 is closed first, the in-cylinder pressure sensor SW4 can accurately measure the reference pressure.

[0068] The ECU 10 then causes the injector 6 to inject fuel for determination into the cylinder 11 whose intake valve 21 is closed at a specific time point after the IVC.

[0069] 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.

[0070] When fuel is injected into the cylinder 11 during the compression stroke, when the temperature and pressure inside the cylinder 11 are gradually increasing, the temperature and pressure inside the cylinder 11 temporarily drop below the reference pressure due to the latent heat of vaporization of the fuel. Then, as the piston 3 rises, the pressure inside the cylinder 11 gradually increases. Over time, the fuel undergoes splitting, atomization, evaporation, and mixing with air, resulting in a low-temperature oxidation reaction. Meanwhile, the temperature and pressure inside the cylinder 11 return to the reference pressure.

[0071] Here, if the properties of the fuel, for example, the boiling point and / or latent heat of vaporization of the fuel, differ, the time it takes for the fuel to evaporate after being injected into the cylinder 11 will differ, and therefore the time it takes for the pressure in the cylinder 11 to return to the reference pressure after dropping below the reference pressure will also change. The dashed line in Figure 3 illustrates an example of the pressure rise when a standard fuel is injected into the cylinder 11. With the standard fuel, the pressure in the cylinder 11 will return to the reference pressure after a reference period tx has elapsed since the intake valve 21 closing timing (IVC), through fuel injection.

[0072] When a different type of fuel with different properties than the standard fuel is injected into the cylinder 11, the pressure inside the cylinder 11 changes due to the difference in evaporation rate. The dotted line in FIG. 3 illustrates the pressure increase when the different type of fuel, which evaporates more easily than the standard fuel, is injected into the cylinder 11. Because the time it takes for the different type of fuel to evaporate is short, the crank angle period from the closing of the intake valve 21 until the pressure inside the cylinder 11 returns to the reference pressure (i.e., measurement period t1) is shorter than the crank angle period for the standard fuel (i.e., reference period tx). The dashed-dotted line in FIG. 3 illustrates the pressure increase when the different type of fuel, which evaporates less easily than the standard fuel, is injected into the cylinder 11. Because the time it takes for the different type of fuel to evaporate is long, the crank angle period from the closing of the intake valve 21 until the pressure inside the cylinder 11 returns to the reference pressure (i.e., measurement period t2) is longer than the crank angle period for the standard fuel.

[0073] The memory 102 stores information about the properties of a standard fuel. Based on the information about the standard fuel, the ECU 10 can obtain a reference period tx from the intake valve 21 closing timing (IVC) until the pressure in the cylinder 11 returns to the reference pressure.

[0074] The ECU 10 acquires, from the measurement signals of the in-cylinder pressure sensor SW4 and the crank angle sensor SW6, a crank angle period t from the closing timing of the intake valve 21 until the pressure value in the cylinder 11 reaches the reference pressure after the injector 6 injects the fuel for determination. The ECU 10 compares the measured crank angle period t with a reference period tx for the standard fuel. If the measured crank angle period t matches the reference period tx, 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 crank angle period t is shorter than the reference period tx, the ECU 10 can determine that the fuel injected by the injector 6 evaporates more easily than the standard fuel. If the measured crank angle period t is longer than the reference period tx, the ECU 10 can determine that the fuel injected by the injector 6 evaporates less easily than the standard fuel.

[0075] Here, the ECU 10 may determine the fuel properties based on only the crank angle period t measured in one cylinder 11. Alternatively, the ECU 10 may measure the crank angle period t not only for one cylinder 11 but also for each of a plurality of cylinders 11 that subsequently enter the compression stroke, and determine the fuel properties based on the average value of the plurality of crank angle periods t. The ECU 10 may measure the crank angle periods t for, for example, four to five cycles.

[0076] When the crank angle period t is measured for 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 fuel injected into the cylinder 11 is more likely to evaporate, and the time it takes to reach the reference pressure is affected by the temperature change inside the cylinder 11.

[0077] Therefore, the ECU 10 may change the length of the reference period tx 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 reference period tx. 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 reference period tx is gradually shortened by a predetermined amount. This eliminates the influence of a gradual increase in the 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 timing and / or the intake valve closing timing (IVC) of the intake valve 21 according to the determined fuel properties. This allows combustion to be equivalent to combustion of standard fuel even if the fuel properties are different, which is advantageous for improving the fuel economy and exhaust gas performance of the engine 100. In addition, an increase in combustion noise can be suppressed.

[0079] 5 shows an example of a fuel injection timing 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 crank angle period minus the reference period, with the left side of the diagram (i.e., negative) indicating that the measured crank angle period t is shorter than the reference period tx, and the right side of the diagram (i.e., positive) indicating that the measured crank angle period t is longer than the reference period tx.

[0080] If the measured crank angle period t is longer than the reference period tx, the fuel is relatively difficult to evaporate. Therefore, the ECU 10 corrects the start of fuel injection (SOI) to the advance side, as shown in the upper diagram of Figure 5. If the start of fuel injection is advanced, the fuel can have more time to evaporate. Even if the fuel is difficult to evaporate, the fuel evaporates at the desired timing, so the combustion is equivalent to that of standard fuel.

[0081] Conversely, if the measured crank angle period t is shorter than the reference period tx, the fuel is relatively prone to evaporation. Therefore, the ECU 10 corrects the start of fuel injection (SOI) to the retard side, as shown in the upper diagram of Figure 5. If the start of fuel injection is delayed, the timing at which fuel evaporation is completed will be delayed, so the fuel will evaporate at the desired timing. Even if the fuel is prone to evaporation, combustion will be equivalent to combustion of standard fuel.

[0082] 5, the longer the measured crank angle period t is relative to the reference period tx, the more the fuel injection start timing is corrected to be advanced, and the shorter the measured crank angle period t is relative to the reference period tx, the more the fuel injection start timing is corrected to be retarded. This allows the fuel evaporation timing to be adjusted appropriately.

[0083] If the fuel injection start timing is advanced too far, the period between the intake valve 21 closing timing and the fuel injection start timing becomes too short, resulting in a low pressure inside the cylinder 11 at the start of fuel injection. If the pressure inside the cylinder 11 is too low, the pressure difference between the fuel injection pressure and the pressure inside the cylinder 11 increases, increasing the penetration of the fuel spray. As a result, the injected fuel adheres to the surfaces of the cylinder 11, preventing the fuel from evaporating. Therefore, an advance limit is set for the fuel injection start timing in the control map shown in the upper diagram of FIG. 5. When the fuel injection start timing reaches the advance limit, the ECU 10 corrects the intake valve 21 closing timing so that the longer the measured crank angle period t is relative to the reference period tx, as shown in the lower diagram of FIG. 5. This increases the temperature and pressure inside the cylinder 11, creating an environment inside the cylinder 11 where the fuel is more likely to evaporate. Even if the fuel is not easily evaporated, combustion is equivalent to that of a standard fuel.

[0084] Furthermore, if the start timing of fuel injection is delayed too much, the end timing of fuel injection approaches the compression top dead center, which shortens the evaporation time of the fuel injected later. This can easily lead to soot generation. Therefore, a retardation limit is set for the start timing of fuel injection in the control map shown in the upper diagram of Figure 5. When the start timing of fuel injection reaches the retardation limit, the ECU 10 corrects the closing timing of the intake valve 21 so that the longer the measured crank angle period t is relative to the reference period tx, as shown in the lower diagram of Figure 5. This reduces the temperature and pressure inside the cylinder 11, slowing the evaporation of the fuel. When fuel is easily evaporated, combustion becomes equivalent to that of standard fuel.

[0085] (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.

[0086] In step S2, the ECU 10 determines whether the intake valve 21 of any cylinder 11 is due to close. If the determination in step S2 is NO, the process repeats step S2. If the determination in step S2 is YES, the process proceeds to step S3.

[0087] In step S3, the ECU 10 determines whether the cylinder 11 that has reached the valve closing timing is the cylinder 11 in the first cycle since the crankshaft 15 started to rotate. If it is the first cycle, the process proceeds to step S11, and if it is the second or subsequent cycle, the process proceeds to step S4.

[0088] In step S11, the ECU 10 stops fuel injection into the cylinder 11. In the subsequent step S12, the ECU 10 measures the pressure in the cylinder 11 from the closing timing of the intake valve 21 to the compression top dead center based on the measurement signal of the in-cylinder pressure sensor SW4. In other words, the ECU 10 measures the reference pressure.

[0089] 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 of the cylinder 11 in the second or subsequent cycles closes. In the following step S5, the ECU 10 acquires the crank angle period t from the closing time of the intake valve 21 to the time when the pressure in the cylinder 11 reaches the reference pressure based on the measurement signals of the in-cylinder pressure sensor SW4 and the crank angle sensor SW6.

[0090] 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 measuring the crank angle period, and may be, for example, 4 to 5 cycles. If the determination in step S6 is NO, the process returns to step S2.

[0091] In addition, from the third cycle onwards, when the process returns to step S3, the ECU 10 executes steps S3 to S5 while changing the reference period tx according to the map in Fig. 4. In this way, fuel injection into the cylinder 11 and measurement of the crank angle period are repeated multiple times.

[0092] If the determination in step S6 is YES, the process proceeds to step S7. ECU 10 calculates the difference between each of the measured crank angle periods t and a reference period tx, and then, in step S8, calculates the average of the differences calculated in step S7. Then, in step S9, ECU 10 determines whether there is a discrepancy between the average of the measured crank angle periods and the reference period. If there is a discrepancy, the process proceeds to step S10, where ECU 10 corrects the fuel injection timing and / or the closing timing of intake valve 21 after engine 100 has started 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 timing and the closing timing of intake valve 21.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] Furthermore, in the above-described configuration, the pressure measured by the in-cylinder pressure sensor SW4 in the cylinder 11 in the first cycle is used as the reference pressure, but this is not limited thereto. The ECU 10 may set the reference pressure by calculating the pressure change in the cylinder 11 during the compression stroke from the temperature and pressure of the intake air supplied to the cylinder 11 based on the measurement signals of the air flow sensor SW1, the intake air temperature sensor SW2, and the intake air pressure sensor SW3. [Explanation of symbols]

[0098] 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. During engine motoring, an in-cylinder pressure sensor outputs a reference pressure signal to a controller, the reference pressure signal being a pressure change in the cylinder of the engine after an intake valve of the cylinder is closed and in the case where no fuel injection is performed; During motoring of the engine after the reference pressure is output, an injector injects fuel for determination into the cylinder at a specific time point after the intake valve closes, the controller acquires a crank angle period from the intake valve closing timing, through the fuel injection, to the time when the pressure in the cylinder reaches the reference pressure, based on a signal from the in-cylinder pressure sensor and a signal from the crank angle sensor; the controller determines the properties of the fuel injected by the injector by comparing a crank angle period from the intake valve closing timing to the time when the standard fuel is injected into the cylinder at the specific time point and the pressure in the cylinder reaches the reference pressure, based on stored information about the properties of the standard fuel, with the acquired crank angle period; How to control the engine.

2. 2. The engine control method according to claim 1, the engine has a plurality of cylinders; The engine control method, wherein the in-cylinder pressure sensor outputs a signal of a reference pressure in a cylinder whose intake valve closes first after the crankshaft of the engine starts to rotate.

3. 3. The engine control method according to claim 2, The injector injects fuel for determination into each of a plurality of cylinders as the engine cycle progresses, the controller obtains a crank angle period for each of the plurality of cylinders; The method of controlling an engine, wherein the controller compares an average value of a plurality of crank angle periods with the crank angle period of the standard fuel.

4. 4. The engine control method according to claim 3, The crank angle period of the standard fuel is shortened with each progression of the cycle.

5. The engine control method according to any one of claims 1 to 4, The engine control method includes correcting at least one of a fuel injection start timing and an intake valve closing timing according to the properties of the fuel after the engine has been started.

6. 6. The engine control method according to claim 5, the controller corrects the start timing of fuel injection to the advance side when the acquired crank angle period is longer than the crank angle period of the standard fuel, and corrects the start timing of fuel injection to the retard side when the acquired crank angle period is shorter than the crank angle period of the standard fuel.

7. 7. The engine control method according to claim 6, the controller corrects the fuel injection start timing to be more advanced as the acquired crank angle period is longer with respect to the crank angle period of the standard fuel, and, when the fuel injection start timing reaches a first period on the advance side, advances the intake valve closing timing to be more advanced as the acquired crank angle period is longer with respect to the crank angle period of the standard fuel.

8. 8. The engine control method according to claim 6 or 7, the controller corrects the fuel injection start timing so that the shorter the acquired crank angle period is with respect to the crank angle period of the standard fuel, the more retarded the fuel injection start timing is, and, when the fuel injection start timing reaches a second period on the retard side, the shorter the acquired crank angle period is with respect to the crank angle period of the standard fuel, the more retarded the intake valve closing timing is.

9. 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 in-cylinder pressure sensor outputs a reference pressure signal that indicates a pressure change after an intake valve of a cylinder of the engine is closed during motoring of the engine, the reference pressure signal corresponding to the pressure in the cylinder when no fuel injection is performed; the controller causes the injector to perform a fuel injection for determination at a specific time point after the intake valve closes during motoring of the engine after the reference pressure is output; the controller acquires a crank angle period from the intake valve closing timing, through the fuel injection, to the time when the pressure in the cylinder reaches the reference pressure, based on the crank angle signal of the crank angle sensor and the pressure signal of the cylinder internal pressure sensor; the controller determines the properties of the fuel injected by the injector by comparing the acquired crank angle period from the closing timing of the intake valve to the time when the standard fuel is injected into the cylinder at the specific time point and the pressure in the cylinder reaches the reference pressure, based on stored information about the properties of the standard fuel.

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