Fuel injection control device and fuel injection control method

Abstract

According to the present invention, in a fuel injection control device (113) and a fuel injection control method for an internal combustion engine (101) having a fuel injection device (301) that injects fuel into an intake port (102), when the fuel injection device (301) performs fuel injection in a high load range of the internal combustion engine (101) in two stages of before an intake valve (119) is opened and while the intake valve (119) is open, an end timing of fuel injection performed before the intake valve (119) is opened is variably set based on information related to an operating condition of the internal combustion engine (101) so that an opening timing of the intake valve (119) falls within a period from when the temperature in the intake port (102) reaches a minimum value to when the temperature in the intake port (102) increases by a set temperature from the minimum value. This makes it possible to maintain an air charge amount in the high load range of the internal combustion engine (101). FIG. 4

Description

Fuel injection control device and fuel injection control method

[0001] The present invention relates to a fuel injection control device and a fuel injection control method that are applied to an internal combustion engine equipped with a fuel injection device that injects fuel into an intake port.

[0002] The fuel injection control device disclosed in Patent Document 1 measures the intake air amount AP before the intake valve opens, and injects fuel in an amount Q1 that is 80% of the supply amount GP based on the intake air amount AP. After the intake valve opens, the intake air amount AS is measured, and the amount Q2 of fuel is injected, which is the supply amount GS based on the intake air amount AS minus the amount Q1.

[0003] Japanese Patent Application Publication No. 11-247681

[0004] In an internal combustion engine equipped with a fuel injection device that injects fuel into an intake port, if fuel is injected twice in the high load range—before the intake valve opens and again while the intake valve is open—then sufficient vaporized fuel flows into the combustion chamber through the fuel injection before the intake valve opens, and then fuel is injected while the intake valve is open, thereby improving the homogeneity of the air-fuel mixture in the cylinder. However, if the fuel injection timing before the intake valve opens is early, although time for fuel vaporization is ensured, the air in the intake port, once cooled by the vaporization of the fuel injected into the intake port, is heated by the heat from the intake port wall before the intake valve opens, causing a problem of an increase in the in-cylinder compression temperature, which in turn leads to a decrease in the air charge amount and a decrease in output torque.

[0005] The present invention has been made in consideration of the current situation, and its purpose is to provide a fuel injection control device and a fuel injection control method that can maintain the air charge amount when fuel is injected twice, before the intake valve opens and while the intake valve is open, under high load conditions in an internal combustion engine.

[0006] Therefore, in one aspect, the fuel injection control device and fuel injection control method of the present invention acquire information regarding the operating state of an internal combustion engine, and when, in a high load range of the internal combustion engine, fuel injection by a fuel injection device that injects fuel into an intake port of the internal combustion engine is performed twice, once before the intake valve of the internal combustion engine opens and once while the intake valve is open, the end timing of the fuel injection before the intake valve opens is variably set based on the information regarding the operating state so that the opening timing of the intake valve is within the period from when the temperature in the intake port drops to when it starts to rise, and an injection control signal corresponding to the end timing is output to the fuel injection device.

[0007] According to the above invention, when the internal combustion engine is under high load, the air charge amount can be maintained when fuel injection is performed twice, once before the intake valve opens and once while the intake valve is open.

[0008] It is a system diagram showing one aspect of an internal combustion engine. It is a flowchart showing the procedure of fuel injection control in a high load range. It is a diagram showing the correlation between the injection end timing and the temperature in the port when the intake valve is open. It is a flowchart showing the details of the injection end timing setting process. It is a diagram for explaining the action and effect of the injection end timing setting process.

[0009] 1 is a block diagram showing an embodiment of an internal combustion engine to which a fuel injection control device and a fuel injection control method according to the present invention are applied.

[0010] 1 is a spark ignition engine that is mounted on, for example, an automobile as a driving source, and includes an ignition device 200 and a fuel supply device 300. The ignition device 200 includes an ignition plug 201 and an ignition coil 202 that incorporates a power transistor, and ignites and burns the air-fuel mixture in the combustion chamber 110 by spark ignition.

[0011] The fuel supply device 300 includes a fuel injection valve 301 as a fuel injection device that injects fuel into the internal combustion engine 101, a fuel tank 302 that stores fuel, an electric fuel pump 303 that pressure-feeds the fuel in the fuel tank 302 to the fuel injection valve 301, a fuel pipe 304 that connects the discharge port of the fuel pump 303 to the fuel inlet of the fuel injection valve 301, a fuel pressure sensor 305 that measures the pressure FP of the fuel in the fuel pipe 304, and a fuel temperature sensor 306 that measures the temperature FT of the fuel in the fuel pipe 304 (in other words, the temperature FT of the fuel supplied to the fuel injection valve 301). The fuel pressure FP in the fuel pipe 304 is, in other words, the pressure FP of the fuel supplied to the fuel injection valve 301. The fuel temperature FT in the fuel pipe 304 is, in other words, the temperature FT of the fuel supplied to the fuel injection valve 301.

[0012] The fuel injection valve 301 is attached to the intake port 102 upstream of the intake valve 119 so as to be directed toward the intake valve 119, and injects fuel into the intake port 102. Therefore, the internal combustion engine 101 is a so-called port injection type internal combustion engine. The fuel injection valve 301 is equipped with an atomization promotion mechanism that promotes atomization of the fuel spray by, for example, forming a vortex flow in the fuel spray.

[0013] In addition to or in addition to the mechanism for turning the fuel spray into a vortex flow, the fuel injection valve 301 may be provided with an atomization promotion mechanism such as a mechanism for making an air flow collide with the fuel spray or a mechanism for heating the fuel before it is injected from the nozzle hole. In the fuel supply device 300, the pressure of the fuel supplied to the fuel injection valve 301 is adjusted by controlling the discharge amount of the fuel pump 303, that is, by controlling the drive power of the fuel pump 303.

[0014] The electronically controlled throttle 108 includes a throttle valve 108a, a throttle motor 108b, and a throttle opening sensor 108c, and the throttle valve 108a is opened and closed by the throttle motor 108b. The throttle opening sensor 108c outputs a throttle opening signal TPS that indicates the opening of the throttle valve 108a.

[0015] The air that has passed through air cleaner 107 has its flow rate adjusted by throttle valve 108a of electronic throttle 108, and is drawn into combustion chamber 110 via intake valve 119 together with fuel injected from fuel injection valve 301. Crank angle sensor 106 is a sensor that measures the rotation angle of crankshaft 117, detects a protrusion of ring gear 114, and outputs a crank angle signal CA that is a pulse signal that rises every time the crankshaft 117 rotates by a predetermined angle.

[0016] A flow rate detection device 109 is disposed in the intake duct 104 upstream of the electronically controlled throttle 108, and outputs an intake air flow rate signal QAR that is information on the amount of intake air of the internal combustion engine 101. In addition, an exhaust valve 115 controls the combustion gas discharged from a combustion chamber 110 of the internal combustion engine 101, and a catalytic converter 112 disposed in an exhaust pipe 103 of the internal combustion engine 101 purifies the exhaust gas of the internal combustion engine 101 by a built-in three-way catalyst.

[0017] The air-fuel ratio sensor 111 is disposed in the exhaust pipe 103 upstream of the catalytic converter 112, and outputs an air-fuel ratio signal RABF representing information on the exhaust air-fuel ratio in accordance with the oxygen concentration in the exhaust. The exhaust temperature sensor 116 is disposed in the exhaust pipe 103 upstream of the catalytic converter 112, and outputs an exhaust temperature signal TEX representing information on the exhaust temperature [°C] at the inlet of the catalytic converter 112.

[0018] The water temperature sensor 118 outputs a coolant temperature signal TW that is information on the temperature [°C] of the coolant in the coolant jacket 105 of the internal combustion engine 101. The engine control device 113, which functions as a fuel injection control device, is an electronic control device equipped with a microcomputer that includes an MPU (Microprocessor Unit) 126, a ROM (Read Only Memory) 127, and a RAM (Random Access Memory) 128.

[0019] The engine control device 113 acquires information relating to the operating state of the internal combustion engine 101 from the above-mentioned sensors, such as the throttle opening signal TPS, the intake air flow rate signal QAR, the crank angle signal CA, the air-fuel ratio signal RABF, the exhaust temperature signal TEX, the coolant temperature signal TW, the fuel pressure signal FP, and the fuel temperature signal FT. The engine control device 113 then calculates various operation amounts based on the acquired information relating to the operating state of the internal combustion engine 101, and outputs signals of the calculated operation amounts, in other words, control signals, to the ignition coil 202, the fuel injection valve 301, the throttle motor 108b, the fuel pump 303, etc., thereby controlling the operation of the internal combustion engine 101.

[0020] The engine control device 113 includes an analog input circuit 120, an A / D conversion circuit 121, a digital input circuit 122, an output circuit 123, and an I / O circuit 124 in order to receive sensor signals and output manipulated variables to the controlled object. The analog input circuit 120 receives analog signals such as an intake air flow rate signal QAR, a throttle opening signal TPS, an air-fuel ratio signal RABF, an exhaust temperature signal TEX, a coolant temperature signal TW, a fuel pressure signal FP, and a fuel temperature signal FT.

[0021] An analog signal received by the analog input circuit 120 is converted into a digital signal by an A / D conversion circuit 121 and output onto a bus 125. Furthermore, a digital signal such as a crank angle signal CA received by a digital input circuit 122 is output onto the bus 125 via an I / O circuit 124.

[0022] An MPU 126, a ROM 127, a RAM 128, a timer / counter (TMR / CNT) 129, etc. are connected to the bus 125. The MPU 126, the ROM 127, and the RAM 128 exchange data via the bus 125.

[0023] A clock signal is supplied to the MPU 126 from a clock generator 130, and the MPU 126 executes various calculations and processes in synchronization with the clock signal. The ROM 127 is, for example, an EEPROM (Electrically Erasable Programmable Read-Only Memory) that allows data to be erased and rewritten, and stores programs for operating the engine control device 113, setting data, initial values, and the like.

[0024] The information stored in the ROM 127 is taken into the RAM 128 and the MPU 126 via the bus 125. The MPU 126 uses the RAM 128 as a working area for temporarily storing the results of calculations and processing.

[0025] The timer / counter 129 is used to measure time, the number of times, etc. The signals of the operation variables, such as the ignition control signal, the injection control signal, and the fuel pressure control signal calculated by the MPU 126, are output onto the bus 125 and then sent from the output circuit 123 to the ignition coil 202, the fuel injection valve 301, the fuel pump 303, etc. via the I / O circuit 124. The injection control signal is, in other words, an air-fuel ratio control signal.

[0026] The following describes in detail the fuel injection control by the engine control device 113, particularly the fuel injection control in the high load range of the internal combustion engine 101. The high load range of the internal combustion engine 101 is, for example, a state in which the load factor of the internal combustion engine 101 is higher than a threshold value, and is an operating range that is divided by the threshold value into a low load range or a low-to-medium load range in which the load factor of the internal combustion engine 101 is lower than the threshold value.

[0027] In the high load range of the internal combustion engine 101, the engine control device 113 causes the fuel injection valve 301 to inject fuel twice, once before the intake valve 119 opens and once while the intake valve 119 is open. In other words, in the high load range of the internal combustion engine 101, the engine control device 113 executes a split injection process in which the amount of fuel required per combustion cycle is injected twice, once before the intake valve 119 opens and once while the intake valve 119 is open. Note that the amount of fuel required per combustion cycle is a fuel amount based on the fuel injection amount for forming a mixture with a target equivalence ratio.

[0028] 2 is a flowchart showing a procedure for fuel injection control in the high load range of the internal combustion engine 101, which is performed by the engine control device 113. In step S501, the engine control device 113 acquires information about the operating state of the internal combustion engine 101, including the intake air flow rate QAR and the engine rotation speed NE calculated from the crank angle signal CA.

[0029] Next, in step S502, the engine control device 113 determines whether the internal combustion engine 101 is operating in a high load range, which is a range in which split injection processing is performed, based on information such as the intake air flow rate QAR and the engine rotation speed NE. If the internal combustion engine 101 is operating in the high load range, the process proceeds to step S503 and subsequent steps. If the internal combustion engine 101 is not operating in the high load range, that is, if it is operating in the low load range or low to medium load range, the process proceeds to step S512, where injection control is performed for the low load range or low to medium load range, in other words, for the load range excluding the high load range.

[0030] When the internal combustion engine 101 is in a high load range and the process proceeds to step S503 or later, the engine control device 113 implements split injection control in which fuel is injected by the fuel injection valve 301 twice, once before the intake valve 119 opens and once while the intake valve 119 is open. In step S503, the engine control device 113 determines whether the intake valve 119 of the cylinder to be controlled is open based on the crank angle signal CA or the like.

[0031] If the intake valve 119 is not open, the engine control device 113 proceeds to step S504, where it determines whether or not the first fuel injection to be performed before the intake valve 119 opens, in other words, pre-injection, has been performed. If the first fuel injection has not been performed, the engine control device 113 proceeds to step S505, and if the first fuel injection has been performed, it returns to step S503 and waits for the intake valve 119 to open.

[0032] In step S505, the engine control device 113 determines the fuel injection amount for the first fuel injection, i.e., the fuel injection amount before the intake valve 119 opens, based on information such as the intake air flow rate QAR and the engine speed NE, as well as the fuel injection amount ratio setting for the split injections. The engine control device 113 determines the fuel injection amount required per combustion cycle based on information such as the intake air flow rate QAR and the engine speed NE, and sets the fuel injection amount for the first fuel injection to be the fuel injection amount corresponding to the ratio of the determined fuel injection amount to be allocated to the first fuel injection.

[0033] Next, in step S506, the engine control device 113 variably sets the end timing FSE of the first fuel injection based on the operating state of the internal combustion engine 101. Here, the engine control device 113 determines the end timing FSE of the first fuel injection so that the opening timing of the intake valve 119 is within the period from when the air temperature in the intake port 102 drops due to vaporization of the fuel injected in the first fuel injection to when it starts to rise. Note that hereinafter, the period from when the air temperature in the intake port 102 drops due to vaporization of the fuel injected in the first fuel injection to when it starts to rise is also referred to as the in-port temperature drop period.

[0034] In other words, the engine control device 113 variably controls the end timing FSE, which changes the timing of the temperature drop period in the port, so that the fuel injected into the intake port 102 in the first fuel injection before the intake valve 119 opens is vaporized, causing the temperature of the air in the intake port 102 to drop to its lowest point, and so that air with as low a temperature as possible is drawn into the combustion chamber.

[0035] The port temperature decrease period can start, for example, when the rate of decrease of the air temperature in the intake port 102, which is decreasing at a rate exceeding a first threshold due to vaporization of the fuel injected in the first fuel injection, falls below the first threshold, and end when the rate of increase of the air temperature subsequently exceeds a second threshold. The port temperature decrease period can also start when the air temperature in the intake port 102 reaches a minimum value, and end when the temperature has risen by a set temperature from the air temperature at the start.

[0036] By variably controlling the end timing FSE, the engine control device 113 maintains the air charge amount by lowering as much as possible the air temperature when the fuel injected in the first fuel injection is drawn in as the intake valve 119 opens, when fuel is injected twice, once before the intake valve 119 opens and once while the intake valve is open, under high load of the internal combustion engine 101. Note that the variable control of the end timing FSE of the first fuel injection will be described in more detail later.

[0037] In the next step S507, the engine control device 113 sets the start timing ESS of the first fuel injection to a point preceding the end timing FSE set in step S506 by an injection time equivalent to the amount of fuel injected in the first fuel injection so that the first fuel injection ends at the end timing FSE set in step S506. Then, the engine control device 113 outputs an injection control signal, in other words, an injection pulse signal, to the fuel injection valve 301 so that the first fuel injection by the fuel injection valve 301 begins at the start timing ESS.

[0038] On the other hand, if the engine control device 113 determines in step S503 that the intake valve 119 is open, the process proceeds to step S508 to control the second fuel injection while the valve is open. In step S508, the engine control device 113 determines whether the second fuel injection (in other words, the main injection) to be performed while the intake valve 119 is open has been performed.

[0039] If the second fuel injection has already been performed, the engine control device 113 ends this routine, and if the second fuel injection has not yet been performed, the engine control device 113 proceeds to step S509. In step S509, the engine control device 113 sets the fuel injection amount for the second fuel injection, that is, the fuel injection while the intake valve 119 is open.

[0040] The engine control device 113 can set the fuel injection amount in the second fuel injection to an amount obtained by subtracting the amount of fuel injected in the first fuel injection from the fuel injection amount required per combustion cycle calculated when calculating the fuel injection amount in the first fuel injection. Furthermore, when calculating the fuel injection amount in the second fuel injection, the engine control device 113 can calculate the fuel injection amount required per combustion cycle anew from the operating state of the internal combustion engine 101 at that time, and set the fuel injection amount in the second fuel injection to an amount obtained by subtracting the fuel injected in the first fuel injection from the newly calculated fuel injection amount required per combustion cycle.

[0041] Next, in step S510, the engine control device 113 sets the timing of the second fuel injection. Here, the engine control device 113 can, for example, set the injection start timing of the second fuel injection as a fixed timing and cause the fuel injection valve 301 to inject fuel for a period of time corresponding to the fuel injection amount from the injection start timing. Furthermore, when the opening period of the intake valve 119 and the opening period of the exhaust valve 115 overlap, the engine control device 113 can cause the fuel injection valve 301 to perform the second fuel injection during the fuel injection period from after the exhaust valve 115 closes to the timing when the deceleration of the intake air flow velocity reaches its maximum.

[0042] After setting the timing of the second fuel injection in step S510, the engine control device 113 then outputs an injection control signal to the fuel injection valve 301 in step S511 to execute the second fuel injection while the intake valve 119 is open. When the engine control device 113 injects the fuel injection amount allocated to the second fuel injection during the fuel injection period from after the exhaust valve 115 closes to the timing when the deceleration of the intake air flow velocity reaches its maximum, the engine control device 113 adjusts the fuel pressure supplied to the fuel injection valve 301 to change the amount of fuel injected during the fuel injection period.

[0043] The following describes in more detail the process for setting the end timing FSE of the first fuel injection before the opening of the intake valve 119. Figure 3 is a diagram showing the change in air temperature in the intake port 102 that accompanies vaporization of the fuel injected in the first fuel injection, for each of three different end timings FSE1, FSE2, and FSE3 of the first fuel injection.

[0044] When fuel is injected into intake port 102 before intake valve 119 opens, the fuel vaporizes, cooling the air in intake port 102 and lowering its temperature. Thereafter, the temperature of the air in intake port 102 begins to rise as it receives heat from the wall surface of intake port 102.

[0045] 3 is the most advanced end timing FSE among the three end timings FSE1, FSE2, and FSE3, and has the longest time from the first end timing FSE1 to the opening timing IVO of the intake valve 119. When the first fuel injection is performed in accordance with the first end timing FSE1, the temperature of the air in the intake port 102 drops once and then begins to rise before reaching the opening timing IVO of the intake valve 119.

[0046] Therefore, if the first fuel injection is performed at the first end timing FSE1, the air in the intake port 102 will be drawn into the combustion chamber 110 after its temperature has risen above the lowest point due to vaporization of the fuel. On the other hand, the second end timing FSE2 shown in Figure 3 is the most delayed end timing FSE among the three end timings FSE1, FSE2, and FSE3, and has the shortest time from the second end timing FSE2 to the opening timing IVO of the intake valve 119.

[0047] If the first fuel injection is performed at the second end timing FSE2, the intake valve 119 opens at timing IVO while the temperature of the air in the intake port 102 is still decreasing due to the vaporization of the injected fuel, i.e., before the temperature of the air in the intake port 102 has completely decreased. Therefore, if the first fuel injection is performed at the second end timing FSE2, the air in the intake port 102 is drawn into the combustion chamber 110 at its highest temperature, just before the temperature of the air decreases most due to the vaporization of the fuel.

[0048] 3 is an end timing FSE sandwiched between the first end timing FSE1 and the second end timing FSE2, and the time from the third end timing FSE3 to the opening timing IVO of the intake valve 119 is an intermediate value. When the first fuel injection is performed in accordance with the third end timing FSE3, the opening timing IVO of the intake valve 119 occurs within the period from when the temperature of the air in the intake port 102 drops to when it starts to rise, that is, within the port temperature drop period, and the intake valve 119 opens when the temperature of the air in the intake port 102 has dropped to its lowest point due to the vaporization of fuel.

[0049] Therefore, if the first fuel injection is performed at the third end timing FSE3, the air in the intake port 102 will be drawn into the combustion chamber 110 at the lowest temperature due to vaporization of the fuel. In other words, if the first fuel injection is performed at the third end timing FSE3 when the intake valve 119 opens during the port temperature drop period, the temperature of the air drawn into the combustion chamber 110 when the intake valve 119 opens will be the lowest, thereby making it possible to lowest the in-cylinder compression temperature and maximize the amount of air charged.

[0050] Therefore, the engine control device 113 advances or retards the end timing FSE of the first fuel injection based on the operating state of the internal combustion engine 101, which affects the time from the end timing FSE of the first fuel injection to the start of the port temperature decrease period, so that the intake valve 119 opens within the port temperature decrease period even if the operating state of the internal combustion engine 101 changes. As a result, the engine control device 113 can maintain a high air charge amount by drawing air that is as cool as possible into the combustion chamber in a high load range of the internal combustion engine 101, and can also draw the fuel injected in the first fuel injection before the intake valve 119 opens into the combustion chamber in a sufficiently vaporized state, and can further improve in-cylinder homogeneity by performing the second fuel injection while the intake valve 119 is open.

[0051] Fig. 4 is a flowchart showing details of the process for varying the end timing FSE in step S506 of the flowchart in Fig. 2. In this embodiment, the end timing FSE for the first fuel injection is expressed as an advance value from the exhaust top dead center.

[0052] First, in step S601, the engine control device 113 acquires information about the operating state of the internal combustion engine 101, such as the intake air flow rate QAR and the engine rotation speed NE, more specifically, information about the operating state of the internal combustion engine 101 that affects the time from the end timing FSE to the start of the port temperature decrease period. Then, as will be described later, the engine control device 113 changes the basic end timing FSEb in accordance with the operating state of the internal combustion engine 101, thereby determining the end timing FSE at which the intake valve 119 opens within the port temperature decrease period, even if the operating state of the internal combustion engine 101 differs.

[0053] In step S602, the engine control device 113 decreases the correction coefficient K1 based on the intake air flow rate QAR in response to an increase in the intake air flow rate QA, so that the end timing FSE is retarded as the intake air flow rate QAR increases. The reason for setting the correction coefficient K1 is that, as the intake air flow rate QA increases, the internal combustion engine 101 generates more thermal energy, increasing the amount of heat received by the air in the intake port 102 from the port wall, shortening the time from the end timing FSE until the port temperature decrease period begins. A shorter time from the end timing FSE until the port temperature decrease period begins means that the decrease in air temperature due to fuel vaporization stops earlier.

[0054] Next, in step S603, the engine control device 113 increases the correction coefficient K2 based on the engine speed NE in response to an increase in the intake air flow rate QA so that the end timing FSE is advanced as the engine speed NE increases. The reason for setting the correction coefficient K2 in this manner is that the time per unit crank angle becomes shorter as the engine speed NE increases.

[0055] Furthermore, in step S604, if the internal combustion engine 101 is equipped with a variable valve timing mechanism that varies the opening and closing timing of the intake valve 119, the engine control device 113 increases the correction coefficient K3 based on the opening timing IVO of the intake valve 119 in accordance with the advancement of the opening timing IVO so that the end timing FSE advances as the opening timing IVO advances. The reason for setting the correction coefficient K3 is that the period from the end timing FSE to the opening timing IVO becomes shorter as the opening timing IVO advances.

[0056] If the internal combustion engine 101 does not have a variable valve timing mechanism, the engine control device 113 fixes the correction coefficient K3 to 1.0 and stops changing the end timing FSE using the correction coefficient K3, that is, stops changing the end timing FSE using the opening timing IVO of the intake valve 119. Also, if the internal combustion engine 101 has a variable compression ratio mechanism that varies the mechanical compression ratio, the engine control device 113 decreases the correction coefficient K4 based on the mechanical compression ratio as the mechanical compression ratio increases, so that the end timing FSE is retarded as the mechanical compression ratio increases. The mechanical compression ratio may be either a target value in variable control of the mechanical compression ratio or an actual mechanical compression ratio.

[0057] The reason for setting the correction coefficient K4 is that when the mechanical compression ratio is high, the compression temperature rises and the amount of heat received by the air in the intake port 102 from the port wall increases, shortening the time from the end timing FSE until the port temperature decrease period begins. Note that if the internal combustion engine 101 does not have a variable compression ratio mechanism, the engine control device 113 fixes the correction coefficient K4 to 1.0 and stops changing the end timing FSE based on the correction coefficient K4, i.e., stops changing the end timing FSE based on the mechanical compression ratio.

[0058] In step S606, the engine control device 113 decreases the fuel temperature-based correction coefficient K5 as the fuel temperature increases so that the end timing FSE is delayed as the fuel temperature increases. The reason for setting the correction coefficient K5 is that a high fuel temperature promotes vaporization and shortens the time from the end timing FSE until the port temperature decrease period begins.

[0059] Furthermore, in step S607, when the internal combustion engine 101 uses alcohol-blended gasoline as fuel, the engine control device 113 increases the correction coefficient K6 based on the alcohol concentration of the fuel as the alcohol concentration increases, so that the end timing FSE is advanced as the alcohol concentration increases. The reason for setting the correction coefficient K6 is that the amount of heat generated decreases as the alcohol concentration increases, and the time from the end timing FSE until the port temperature decrease period begins becomes longer. Note that a longer time from the end timing FSE until the port temperature decrease period begins means that the decrease in air temperature due to fuel vaporization will cease later.

[0060] If the internal combustion engine 101 does not use alcohol-blended gasoline, the engine control device 113 fixes the correction coefficient K6 to 1.0 and stops changing the end timing FSE based on the correction coefficient K6, that is, stops changing the end timing FSE based on the alcohol concentration. Next, in step S608, the engine control device 113 multiplies the basic end timing FSEb by the correction coefficient K1-K6 set in steps S602 to S607, and sets the result as the final end timing FSE.

[0061] Then, in step S506, the engine control device 113 controls the injection start timing so that the first fuel injection ends at the end timing FSE. As a result, even if the operating conditions, such as the intake air flow rate QAR, vary, the intake valve 119 opens within the period of decrease in the port temperature that occurs as the fuel injected in the first fuel injection vaporizes. Therefore, when the intake valve 119 opens in the high load range of the internal combustion engine 101, air with the lowest possible temperature is drawn into the fuel chamber 10, keeping the in-cylinder compression temperature low and maintaining the air charge amount.

[0062] 5 is a diagram illustrating the effect of the engine control device 113 controlling the end timing FSE of the first fuel injection so that the intake valve 119 opens within the temperature drop period in the port. In the example shown in FIG. 5, when the end timing FSE is set to 90 degrees before the exhaust top dead center, the intake valve 119 opens within the temperature drop period in the port, and the air temperature in the port when the intake valve 119 opens becomes the lowest.

[0063] In other words, whether the end timing FSE is advanced or retarded from 90 degrees before exhaust top dead center, the port air temperature when the intake valve 119 opens will be higher than when the end timing FSE is set to 90 degrees before exhaust top dead center. Therefore, the engine control device 113 sets the end timing FSE at which the intake valve 119 opens within the port temperature decrease period based on the operating state of the internal combustion engine 101, thereby maintaining the port air temperature when the intake valve 119 opens as low as possible even if the operating state of the internal combustion engine 101 changes.

[0064] If the air temperature in the port is low when intake valve 119 opens, low-temperature air will be drawn into the combustion chamber, suppressing the compression temperature in the cylinder and increasing the amount of air charged as much as possible. Also, if the first fuel injection is performed at the end timing FSE when the air temperature in the port is lowest when intake valve 119 opens, intake valve 119 will open with sufficient premixing of the fuel injected in the first fuel injection promoted, improving in-cylinder homogeneity.

[0065] The technical ideas described in the above embodiments can be used in appropriate combinations as long as no contradictions arise. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it is obvious that a person skilled in the art can adopt various modified embodiments based on the basic technical ideas and teachings of the present invention.

[0066] For example, in variable control of the end timing of fuel injection before the intake valve 119 opens, the engine control device 113 can change the end timing of fuel injection depending on any of the aforementioned intake air flow rate QA, engine rotation speed NE, etc., as well as the octane number of the gasoline fuel, the air-fuel ratio (target equivalence ratio), air pressure, altitude, outside air humidity, outside air temperature, the on / off state of the atomization promotion mechanism provided in the fuel injection valve 301, and the fuel supply pressure to the fuel injection valve 301.

[0067] Furthermore, if the internal combustion engine 101 is equipped with an air temperature sensor that detects the air temperature in the intake port 102 downstream of the fuel injection valve 301, the engine control device 113 can perform learning control to change the correlation between the operating state of the internal combustion engine 101 and the end timing based on the air temperature in the intake port 102 detected by the air temperature sensor. Furthermore, the engine control device 113 can limit the variable range of the end timing based on the operating state such as the intake air flow rate QA and the engine rotation speed NE to within a set crank angle range, or limit the amount of change per calculation cycle of the end timing based on the operating state such as the intake air flow rate QA and the engine rotation speed NE to equal to or less than a set value.

[0068] 101... internal combustion engine, 102... intake port, 113... engine control device (fuel injection control device), 119... intake valve, 301... fuel injection valve (fuel injection device)

Claims

1. A fuel injection control device applied to an internal combustion engine equipped with a fuel injection device that injects fuel into an intake port, the fuel injection control device being configured to acquire information regarding the operating state of the internal combustion engine, and when fuel injection by the fuel injection device is performed twice in a high load range of the internal combustion engine, once before the intake valve of the internal combustion engine opens and once while the intake valve is open, variably set the end timing of the fuel injection before the intake valve opens based on the information regarding the operating state so that the opening timing of the intake valve is within the period from when the temperature in the intake port drops to when it starts to rise, and output an injection control signal according to the end timing to the fuel injection device.

2. A fuel injection control device according to claim 1, wherein the end timing is delayed as the amount of intake air into the internal combustion engine increases.

3. A fuel injection control device according to claim 1, wherein the higher the rotation speed of the internal combustion engine, the more the end timing is advanced.

4. A fuel injection control device according to claim 1, wherein the more the opening timing of the intake valve is advanced, the more the end timing is advanced.

5. A fuel injection control device according to claim 1, wherein the higher the mechanical compression ratio of the internal combustion engine, the more the end timing is delayed.

6. A fuel injection control device according to claim 1, wherein the higher the temperature of the fuel, the more the end timing is delayed.

7. A fuel injection control device according to claim 1, wherein the higher the alcohol concentration in the fuel, the more advanced the end timing is.

8. A fuel injection control device according to claim 1, wherein the period from when the temperature inside the intake port starts to decrease until it starts to increase is the period from when the rate at which the temperature inside the intake port starts to decrease slows below a first threshold value until when the rate at which the temperature inside the intake port starts to increase becomes faster than a second threshold value.

9. A fuel injection control device according to claim 1, wherein the period from when the temperature inside the intake port drops until it starts to rise is the period from when the temperature inside the intake port reaches a minimum value until it rises by a predetermined temperature.

10. A fuel injection control device according to claim 1, wherein the period from when the temperature in the intake port drops until when it starts to rise is defined as a temperature drop period, and the operating state is a state quantity related to the time from the end timing until the temperature drop period begins.

11. A fuel injection control method applied to an internal combustion engine equipped with a fuel injection device that injects fuel into an intake port, comprising: acquiring information regarding the operating state of the internal combustion engine; and, when fuel injection by the fuel injection device is performed twice in a high load range of the internal combustion engine, once before the intake valve of the internal combustion engine opens and once while the intake valve is open, variably setting the end timing of the fuel injection before the intake valve opens based on the information regarding the operating state so that the opening timing of the intake valve is within the period from when the temperature in the intake port drops to when it starts to rise; and outputting an injection control signal according to the end timing to the fuel injection device.