JP2006348865A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection control device for an internal combustion engine capable of preferably achieving both improvement of engine output and improvement of knock resistance.
SOLUTION: When the intake air temperature detected by the intake air temperature detection means 40 is below a predetermined value, only in-cylinder injection by the first fuel injection valve 2 is executed, and when the intake air temperature exceeds a predetermined value, the first fuel injection valve is executed. The intake passage injection by the second fuel injection valve 33 is executed together with the in-cylinder injection by 2. The intake air temperature can be lowered before the intake gas is introduced into the in-cylinder combustion chamber 28, and the intake charge efficiency and the knock resistance can be improved. Further, the amount of fuel supplied can be increased by the increase in the intake air amount, and high output can be achieved. If the intake air temperature exceeds a predetermined value, the second fuel injection valve 33 is operated, so that intake air cooling can be performed in direct response to the detected intake air temperature.
[Selection] Figure 1

Description

  The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to a fuel injection control device for an internal combustion engine that can inject fuel into both a cylinder combustion chamber and an intake passage.

  There is always a demand to increase the output torque of the engine. For this reason, turbochargers such as turbochargers and superchargers, and intercoolers as necessary, are also installed, due to increased supercharging pressure and lower intake air temperature. It is already known to increase the amount of fuel that can be supplied by improving the charging efficiency of intake air. However, in the case of a gasoline engine, the problem of knocking always exists contrary to this, and how to suppress this knocking is an important theme.

  Here, in the case of a direct-injection gasoline engine, the temperature of the in-cylinder mixture can be directly reduced using the latent heat of vaporization of the fuel injected into the in-cylinder combustion chamber, thereby improving the intake charging efficiency. it can. Therefore, it is advantageous for high output and has a relatively good knock resistance.

  Further, in addition to in-cylinder injection, it is conceivable to inject fuel into the intake passage, and in this way, the intake air before being introduced into the in-cylinder combustion chamber by intake passage injection is cooled using the latent heat of vaporization of the fuel. This is more advantageous for higher output and improved knock resistance.

  For example, Patent Document 1 discloses a related art related to coexistence of such improvement in engine output and improvement in knock resistance. This patent document 1 discloses a fuel injection device for an internal combustion engine that includes a first fuel injection valve that injects fuel into a cylinder and a second fuel injection valve that injects fuel into an intake port. The fuel injection amounts of the first and second fuel injection valves so that the fuel within the range where the filling efficiency is expected to be improved by the latent heat of vaporization of the injected fuel is injected from the first fuel injection valve. It is disclosed to control the proportion of. In the region where the rotational speed of the internal combustion engine is higher than a predetermined level, it is disclosed that the ratio of the fuel injection amount from the second fuel injection valve is set larger as the rotational speed is higher.

JP 2004-270583 A

  However, the technique disclosed in Patent Document 1 only increases or decreases the fuel injection amount ratio between the first fuel injection valve and the second fuel injection valve in accordance with the engine speed, and improves engine output and knock resistance. However, it is not always sufficient to achieve compatibility with the improvement in performance.

  Accordingly, the present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a fuel injection control device for an internal combustion engine that can suitably achieve both improvement in engine output and improvement in knock resistance. There is.

  In order to achieve the above object, a fuel injection control device for an internal combustion engine according to an aspect of the present invention includes a first fuel injection valve that injects fuel into a cylinder combustion chamber and a second fuel injection that injects fuel into an intake passage. A valve, an intake air temperature detecting means for detecting an intake air temperature at a predetermined position of the intake passage, and fuel injection only by the first fuel injection valve when the intake air temperature detected by the intake air temperature detecting means is below a predetermined value When the intake air temperature exceeds the predetermined value, the fuel injection by the second fuel injection valve is executed in conjunction with the fuel injection by the first fuel injection valve. And an injection valve control means for controlling the injection valve.

  According to this aspect of the present invention, when the intake air temperature exceeds a predetermined value, the intake passage injection by the second fuel injection valve is executed together with the in-cylinder injection by the first fuel injection valve. Accordingly, the intake air temperature can be lowered using the latent heat of vaporization of the fuel injected from the second fuel injection valve before the intake air is introduced into the in-cylinder combustion chamber, so that the charging efficiency of the intake air is increased and the knock resistance is improved. Can do. Further, the amount of fuel supplied into the in-cylinder combustion chamber can be increased by the increase in the intake air amount, and high output can be achieved. In particular, if the intake air temperature detected at a predetermined position in the intake passage exceeds a predetermined value, the second fuel injection valve is operated, so that intake air cooling can be performed in direct response to the detected intake air temperature. Purposeful.

  Here, it is preferable that the apparatus further includes a supercharger and an intercooler provided on the intake air downstream side of the supercharger, and the second fuel injection valve is provided on the downstream side of the intercooler.

  As is well known, the charging efficiency of intake air can be improved by the supercharger and the intercooler, and the intake air temperature can be lowered, which is advantageous for higher output and improved knock resistance. Since the second fuel injection valve is provided on the downstream side of the intercooler, it is advantageous for cooling the intake air before introducing the combustion chamber.

  Moreover, it is preferable that the intake air temperature detecting means is provided on the downstream side of the intercooler and on the upstream side of the second fuel injection valve.

  Since the intake air temperature detecting means is provided on the downstream side of the intercooler, the intake air temperature after being cooled after passing through the intercooler can be detected, and the necessity of operation of the second fuel injection valve is accurately determined. be able to. Further, since the intake air temperature detecting means is provided on the upstream side of the second fuel injection valve, the intake air temperature detecting means is not affected by the intake air cooling by the second fuel injection valve.

  Further, the valve timing variable means for changing the valve timing of at least one of the intake valve and the exhaust valve, and when the intake air temperature exceeds the predetermined value, the overlap of the intake and exhaust valves is more than the predetermined basic overlap. It is preferable to further include valve timing control means for controlling the valve timing variable means so as to reduce the amount.

  If the overlap is large when fuel injection is performed from the second fuel injection valve, the fuel injected and evaporated for cooling the intake air blows through to the exhaust side together with fresh air, and HC deteriorates. Therefore, by controlling the valve timing variable means so that the overlap is smaller than the predetermined basic overlap in this way, it is possible to prevent fuel blow-through and HC deterioration.

  Here, it is preferable that the valve timing control means executes the control of the valve timing varying means when the intake air temperature exceeds the predetermined value and the engine operating state is in a predetermined blow-through area. The predetermined blow-by area is, for example, a low rotation high load area.

  Preferably, the fuel injection amount injected from the second fuel injection valve is a function of the intake air temperature. For example, the fuel injection amount injected from the second fuel injection valve is increased as the intake air temperature increases, and as a result, the intake air cooling effect can be enhanced by the increase in the intake air temperature.

  Preferably, when the intake air temperature exceeds the predetermined value, the injection valve control means sets or maintains the fuel injection amount of the first fuel injection valve at the value of the fuel injection amount immediately before the first fuel injection valve exceeds the predetermined value. This has the advantage that the control becomes simple.

  According to the present invention, an excellent effect is exhibited that it is possible to suitably achieve both improvement in engine output and improvement in knock resistance.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 schematically shows a fuel injection control device for an internal combustion engine according to the present embodiment. Although the illustrated engine 1 is representatively shown with only one cylinder, it is a multi-cylinder engine and the number of cylinders is not particularly limited. A first fuel injection valve (first injector) 2 that directly injects fuel into the cylinder combustion chamber is provided for each cylinder. Further, the engine 1 is a spark ignition type, more specifically a gasoline engine, which uses alcohol or a mixed fuel of this and gasoline, gaseous fuel such as CNG, and other fuels as an alternative fuel. May be.

  The engine 1 is a supercharged type, and, for example, a turbocharger 3 is provided as a supercharger that supercharges intake air. The turbocharger 3 has a turbine 4 provided in the exhaust system and a compressor 5 provided in the intake system, and drives the turbine 4 using exhaust energy and drives the compressor 5 coaxially connected thereto. The intake air is supercharged. The turbine 4 is provided with a wastegate 6 that bypasses the wastegate 6 and a wastegate valve 7 that opens and closes the wastegate 6. A supercharger can also be used as a supercharger.

  Air sucked from the air cleaner 8 is distributed and supplied to the combustion chambers of the respective cylinders via the intake passage 9. The intake passage 9 is mainly defined by an intake pipe 10, an intake manifold 11 and an intake port 12 arranged in order from the upstream side. The intake pipe 10 is positioned on the compressor 5 and on the downstream side of the compressor 5. An intercooler 13 and an electronically controlled throttle valve 14 located on the downstream side of the intercooler 13 are provided. The intercooler 13 cools the intake air passing through it. The intercooler 13 of the present embodiment is an air cooling type, but may be a water cooling type. The engine 1 of this embodiment is mounted on a vehicle, and the intake air is cooled by exchanging heat with the outside air (particularly traveling wind) via the intercooler 13. The intake manifold 11 includes a surge tank 15 as a collecting portion located on the upstream side, and a plurality of branch pipes 16 connecting the surge tank 15 and the intake port 12 of each cylinder for each cylinder. The intake port 12 is formed in the cylinder head 17 of the engine 1 for each cylinder.

  Similarly, the exhaust passage 18 has an exhaust port 19 formed for each cylinder in the cylinder head 17 of the engine 1, an exhaust manifold 20 connected to the exhaust port 19, and an exhaust pipe connected to the downstream side of the exhaust manifold 20. 21, and the exhaust pipe 21 is provided with the turbine 4.

  The outlet of the intake port 12 is opened and closed by the intake valve 22, and the inlet of the exhaust port 19 is opened and closed by the exhaust valve 23. In the present embodiment, the overlap, which is the overlapping portion of the valve opening period of the intake valve 22 and the exhaust valve 23, is particularly variable. To achieve this, the intake valve 22 and the exhaust valve 23 are respectively electromagnetically driven. The intake valve actuator 24 and the exhaust valve actuator 25 are driven to open and close. The intake valve actuator 24 and the exhaust valve actuator 25 are actuated based on an open / close signal from an electronic control unit (hereinafter referred to as ECU) 100, whereby the intake valve 22 and the exhaust valve 23 are opened and closed at an arbitrary timing and lift. Is possible. As described above, in this embodiment, the intake valve actuator 24 and the exhaust valve actuator 25 serve as valve timing variable means, and the ECU 100 serves as valve timing control means.

  It is important to note that the overlap is variable here. Therefore, the valve timing variable means is not limited to the actuators 24 and 25. For example, the camshaft that drives the intake valve (and / or the exhaust valve) to open / close is advanced or retarded so that the opening / closing timings of the intake valves (and / or exhaust valves) of all the cylinders are set to the same operating angle. A variable valve timing mechanism (so-called VVT) that advances or retards all at once while maintaining it may be adopted as the valve timing variable means. Further, the intake valve actuator 24 and the exhaust valve actuator 25 may be hydraulically or pneumatically operated. Valve timing varying means may be provided for only one of the intake valve 22 and the exhaust valve 23.

  A piston 27 is disposed in the cylinder 26 of the engine 1 so as to be able to reciprocate. A cylinder combustion chamber 28 is defined above the piston 27. A spark plug 29 is attached to the cylinder head 17 so as to face the in-cylinder combustion chamber 28, and the piston 27 is connected to the crankshaft 31 via a connecting rod 30.

  The first fuel injection valve 2 performs fuel injection in one or both of the intake stroke and the compression stroke. In the case of compression stroke injection, fuel and air are mixed in the process of injecting fuel toward the concave portion 32 at the top of the rising piston 27 and generating a tumble-like flow that winds up along the inner surface of the concave portion 32. A relatively rich air-fuel mixture layer is formed in the vicinity of the spark plug 29. A lean air-fuel mixture layer or air layer is formed around the rich air-fuel mixture layer, whereby the air-fuel mixture in the in-cylinder combustion chamber 28 is stratified and stratified combustion is realized. The first fuel injection valve 11 is opened by a drive signal from the ECU 100 to inject fuel, and when the drive signal from the ECU 100 stops, the first fuel injection valve 11 is closed to stop fuel injection. The air-fuel mixture in the cylinder combustion chamber 28 is ignited by the spark plug 29 based on the ignition signal from the ECU 100 and burns. The exhaust in the in-cylinder combustion chamber 28 is exhausted through the exhaust passage 18.

  Here, in particular, the intake passage 9 is provided with a second fuel injection valve (second injector) 33 for injecting fuel into the intake passage 9. The second fuel injection valve 33 is provided to cool the intake air in the intake passage 9 before being introduced into the in-cylinder combustion chamber 28 using the latent heat of vaporization of the fuel. The second fuel injection valve 33 is preferably provided on the downstream side of the intercooler 13, and in the present embodiment, the second fuel injection valve 33 is provided in the surge tank 15 and injects fuel therein. In the present embodiment, there is one second fuel injection valve 33, which is common to each cylinder. Similarly to the first fuel injection valve 2, the second fuel injection valve 33 is opened by a drive signal from the ECU 100 to inject fuel, and when the drive signal from the ECU 100 stops, the valve is closed to stop fuel injection. Thus, the 1st fuel injection valve 2 and the 2nd fuel injection valve 33 are provided, and the engine 1 is comprised as what is called a dual injection type.

  The installation position and number of the second fuel injection valves are not limited to the above. For example, one second fuel injection valve may be provided for each branch pipe 16, that is, for each cylinder.

  Although not shown, the fuel in the fuel tank is supplied to the first fuel injection valve 2 and the second fuel injection valve 33 via a fuel supply device (not shown). High pressure fuel is supplied to the first fuel injection valve 2 by a high pressure pump, and the injection pressure of the main injection by the first fuel injection valve 2 is higher than that of the auxiliary injection by the second fuel injection valve 33.

  The ECU 100 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like, receives input signals from various sensors, performs predetermined processing based on the signals, The first fuel injection valve 2, the second fuel injection valve 33, the spark plug 29, the intake valve actuator 24, the exhaust valve actuator 25, the drive motor 34 for the throttle valve 14, the drive actuator 35 for the waste gate valve 7, and the like are controlled.

  The sensors include an intake air temperature sensor 40, an intake pressure sensor 41, a water temperature sensor 42, a crank angle sensor 43, a throttle opening sensor 44, and an accelerator opening sensor 45. The intake air temperature sensor 40 is for detecting the intake air temperature at the position where it is installed, and is preferably installed downstream of the intercooler 13. In this embodiment, the upstream side of the surge tank 15, that is, the second fuel injection. Installed upstream of the valve 33. The intake pressure sensor 41 is for detecting the intake pressure at the position where the intake pressure sensor 41 is installed, and is installed in the surge tank 15 in this embodiment. The water temperature sensor 42 is for detecting the cooling water temperature of the engine 1. The cooling water temperature is a representative value of the engine temperature, which can be replaced with an oil temperature or the like. The crank angle sensor 43 is for detecting the angle or phase of the crankshaft 31, and is a non-contact type sensor constituted by an electromagnetic pickup or the like. Each time the teeth of a toothed rotor provided on the crankshaft 31 pass through. Output a pulse. The throttle opening sensor 44 is for detecting the opening of the throttle valve 14 (throttle opening). The accelerator opening sensor 45 is for detecting an accelerator pedal opening (accelerator opening) or a depression amount.

  The ECU 100 calculates a load required for the engine 1 based on the intake pressure detected by the intake pressure sensor 41. The ECU 100 detects the crank angle of the engine 1 based on the output pulse of the crank angle sensor 43 and calculates the rotation speed. The ECU 100 normally controls the drive motor 34 so that the output value of the throttle opening sensor 44 becomes a value corresponding to the output value of the accelerator opening sensor 45, and links the throttle opening to the accelerator opening.

  Next, fuel injection control of the internal combustion engine in the present embodiment will be described.

  In the present embodiment, the second fuel injection valve 33 is mainly intended to lower the intake air temperature, and is operated only when the intake air temperature exceeds a predetermined value. That is, the ECU 100 executes fuel injection only by the first fuel injection valve 2 when the intake air temperature THIN detected by the intake air temperature sensor 40 is equal to or lower than the predetermined value THH, and when the intake air temperature THIN exceeds the predetermined value THH. The first fuel injection valve 2 and the second fuel injection valve 33 are controlled so that the fuel injection by the second fuel injection valve 33 is executed in conjunction with the fuel injection by the first fuel injection valve 2. The fuel injection by the first fuel injection valve 2 is called main injection, and the fuel injection by the second fuel injection valve is called auxiliary injection.

  When the engine 1 is operated, for example, when the accelerator pedal is greatly depressed, the required load on the engine 1 becomes very large, and the engine operation state enters a high load region, for example, a full load region called WOT (Wide Open Throttle). Then, the turbocharger 3 is remarkably operated, the supercharging pressure reaches almost the maximum value, and the intake air temperature rises remarkably. In such a situation, the intake air temperature can be lowered below the allowable value via the intercooler 13 if the vehicle is traveling at high speed, but if not, high temperature intake air exceeding the allowable value is introduced into the in-cylinder combustion chamber 28. It can happen. In this case, it is difficult to sufficiently cool the intake air in the in-cylinder combustion chamber 28 even by utilizing the latent heat of vaporization of the main injection, which is in-cylinder injection, and not only high charging efficiency can be obtained, but also knocking is prevented. May occur. As a result, knocking control such as retarding the ignition timing is inevitably executed, and high output from the engine 1 cannot be expected. Therefore, the aim of the present invention is to lower the temperature of the intake air in advance before it is introduced into the in-cylinder combustion chamber 28 by auxiliary injection in order to improve the knock resistance.

  FIG. 2 shows a fuel injection control routine of this embodiment. This routine is repeatedly executed by the ECU 100 for each injection cycle. In the following description, a step is represented by S.

  First, the ECU 100 calculates a basic injection amount Qt, which is the total fuel injection amount to be injected in the injection cycle, with reference to a predetermined map based on the engine operating state at that time (S101). Here, the engine operating state is, for example, the rotational speed and the load. As described above, the rotational speed is calculated by the ECU 100 based on the output signal of the crank angle sensor 43, and the load is based on the output signal of the intake pressure sensor 41. Calculated by the ECU 100. Note that an air flow meter for detecting the intake flow rate may be provided to calculate the load based on the output value thereof. The map is created in advance based on an actual machine test or the like and stored in the ROM of the ECU 100, and the basic injection amount Qt corresponding to the rotation speed and the load is input. The basic injection amount Qt is basically set as a fuel amount to be injected in the main injection.

  Next, the ECU 100 acquires the intake air temperature THIN detected by the intake air temperature sensor 40, and determines whether or not the intake air temperature THIN is greater than a predetermined value THH stored in advance in the ROM of the ECU 100 (S102). ). The predetermined value THH is set as the maximum allowable temperature of the intake air introduced into the in-cylinder combustion chamber 28, and is a constant value in this embodiment. However, the predetermined value THH may be a value according to the engine operating state (for example, the rotation speed and the load).

  When it is determined that the intake air temperature THIN is equal to or lower than the predetermined value THH, the ECU 100 temporarily stores the value of the basic injection amount Qt calculated in S101 in the RAM as the set injection amount Qf (S108). Simultaneously with the arrival of the predetermined injection start timing, the first fuel injection valve 2 is energized (ON) for a time corresponding to the basic injection amount Qt, and an amount of fuel equal to the basic injection amount Qt is supplied from the first fuel injection valve 2. Inject (S109). Here, the injection start timing is set within the period of the compression stroke, and for example, the compression stroke in-cylinder injection that performs the stratified combustion as described above is executed. As a result, the routine ends. Eventually, when the intake air temperature THIN is equal to or lower than the predetermined value THH, fuel injection is executed only by the first fuel injection valve 2.

  On the other hand, when it is determined in S102 that the intake air temperature THIN has exceeded the predetermined value THH, the ECU 100 determines whether or not the engine operating state is in a predetermined blow-through area (S103). This determination is made with reference to a predetermined map shown in FIG. This map is also created in advance based on an actual machine test and stored in the ROM of the ECU 100. The ECU 100 determines whether or not the rotation speed and load calculated in S101 are in the blow-through area A indicated by hatching in the map. The blow-by area A is set to the low rotation and high load side.

  When it is determined that the engine operating state is in the predetermined blow-through area, the ECU 100 sets the operation timing of the intake valve actuator 24 and the exhaust valve actuator 25 so that the overlap of the intake and exhaust valves is reduced (S104). Here, the operation timing of the intake valve actuator 24 and the exhaust valve actuator 25 (that is, the valve timing of the intake / exhaust valve) is determined in advance by a map or the like based on the engine operating state (for example, the rotational speed and load), Therefore, the basic overlap required from now on is also determined in advance based on the engine operating state. On the other hand, in S104, an overlap smaller than such a basic overlap is set. For example, the opening operation timing of the intake valve actuator 24 (that is, the intake valve opening timing) is delayed from the basic timing, thereby reducing the overlap from the basic overlap.

  Generally, in a direct injection engine, the overlap is set to a relatively large value on the low rotation and high load side. This is because a large amount of air is taken into the in-cylinder combustion chamber due to the intake and exhaust pulsation. For the same reason, the engine of the present embodiment also has a large overlap during normal times and at a low rotation and high load. However, even if auxiliary injection is performed from the second fuel injection valve 33, assuming that the overlap is large, the time per engine revolution is long at low revolutions, and the suction is high under high load, that is, high boost pressure. Since the atmospheric pressure becomes higher than the back pressure, the auxiliary fuel injected and evaporated for cooling the intake air blows out to the exhaust side together with fresh air, and HC deteriorates. Therefore, in such a case, overlap is reduced to prevent blow-through and HC deterioration.

  On the other hand, when it is determined in S103 that the engine operating state is not in the predetermined blow-by region, the ECU 100 skips S104. That is, the overlap is a relatively large value during normal times.

  Next, the ECU 100 calculates an auxiliary injection amount Qs, which is the amount of fuel to be injected from the second fuel injection valve 33, based on a predetermined map as shown in FIG. 5 (S105). This map will be described in detail later.

  The ECU 100 energizes (turns on) the second fuel injection valve 33 for a time corresponding to the auxiliary injection amount Qs simultaneously with the arrival of the predetermined injection start timing, and supplies the second fuel with an amount of fuel equal to the auxiliary injection amount Qs. The fuel is injected from the injection valve 33 (S106). Here, the injection start timing is set so that the fuel injection by the second fuel injection valve 33 ends before the intake valve opens. The injection start timing may be set so that at least a part of the fuel injection period of the second fuel injection valve 33 overlaps the intake valve opening period, that is, synchronous injection is performed.

  Thereafter, the ECU 100 energizes (turns on) the first fuel injection valve 2 for a time corresponding to the set injection amount Qf stored in S108 at the same time as the predetermined injection start timing within the compression stroke period, for example, and sets the set injection amount. An amount of fuel equal to Qf is injected from the first fuel injection valve 2 (S107). As a result, the routine is terminated. Eventually, when the intake air temperature THIN exceeds the predetermined value THH, the fuel injection by the second fuel injection valve 33 is executed together with the fuel injection by the first fuel injection valve 2. As a result of the fuel injection by the second fuel injection valve 33, the air-fuel mixture formed in the in-cylinder combustion chamber forms a lean air-fuel mixture layer, for example, around a rich air-fuel mixture layer near the spark plug. It should be called a weak stratification. If the intake air temperature THIN once exceeds the predetermined value THH and the state continues, the set injection amount Qf is not updated in S108, so that the set injection stored immediately before the intake air temperature THIN exceeds the predetermined value THH. The quantity Qf is continuously injected from the first fuel injection valve 2.

  Next, how each value changes when such control is performed will be described with reference to FIG. In the figure, changes in the intake air temperature, the air-fuel ratio, and the fuel injection amount as the intake pressure increases are shown. In this case, the increase in intake pressure is synonymous with an increase in supercharging pressure, an increase in load, an increase in throttle opening, an increase in accelerator opening, acceleration of an engine or a vehicle, and the like. As the intake pressure and the intake temperature, values detected by the intake pressure sensor 41 and the intake temperature sensor 40 are used, respectively. This figure shows a case where the engine speed is constant at a certain value.

  As can be seen, when the intake air temperature THIN is equal to or lower than the predetermined value THH, fuel injection is performed only by the first fuel injection valve 2. At this time, the main injection amount Qm and the intake air temperature THIN rise as the intake air pressure increases. The air-fuel ratio is feedback-controlled using an air-fuel ratio sensor (not shown), and is maintained at a relatively high predetermined value that is advantageous for fuel consumption.

  When the intake air temperature THIN exceeds a predetermined value THH, fuel injection is also performed from the second fuel injection valve 33. At this time, the auxiliary injection amount Qs injected from the second fuel injection valve 33 is calculated based on the map shown in FIG. This map is stored in advance in the ROM of the ECU 100. As can be seen in FIG. 5, the auxiliary injection amount Qs is a function of the intake air temperature THIN, and the auxiliary injection amount Qs increases as the intake air temperature THIN increases. When the intake air temperature THIN is a predetermined value THH, the auxiliary injection amount Qs is the minimum Qsmin. The minimum auxiliary injection amount Qsmin is set equal to the minimum injection amount of the second fuel injection valve 33 determined from the structure of the second fuel injection valve 33, for example. Note that the value of the auxiliary injection amount Qs itself is desirably a value that evaporates before the fuel is introduced into the in-cylinder combustion chamber 28.

  By supplying the auxiliary fuel, the intake air temperature THIN is reduced as compared with the case where the fuel injection is performed only by the main injection. The reduction width is indicated by ΔT. While the intake air temperature THIN exceeds the predetermined value THH, the main injection amount Qm is kept constant at the main injection amount Qm1 immediately before the intake temperature THIN exceeds the predetermined value THH. Immediately after the intake air temperature THIN exceeds the predetermined value THH, as a result of adding the auxiliary injection amount Qsmin (strictly speaking, the auxiliary injection amount slightly larger than this) to the main injection amount Qm1, the air-fuel ratio decreases stepwise (that is, , The value on the rich side). If the intake pressure when the intake air temperature THIN exceeds the predetermined value THH is PBH, the intake air temperature THIN increases as the intake air pressure increases from PBH, and the auxiliary injection amount Qs increases accordingly, and the air-fuel ratio becomes It goes down (that is, it gradually becomes richer). Such a decrease in the air-fuel ratio is not always desirable from the viewpoint of fuel consumption requirements, but in situations where high supercharging and high load operation are required such that the intake air temperature THIN exceeds the predetermined value THH. The output should be prioritized rather than the fuel consumption, and therefore the decrease in the air-fuel ratio is not a problem.

  Here, the fixed maintenance value Qm1 of the main injection amount will be described. When the determination in S102 is switched from NO to YES in the routine shown in FIG. 2, the setting stored in S108 in the cycle one time before the switching is performed. The injection amount Qf is Qm1. Thereafter, as long as the determination in S102 is YES, Qf = Qm1 is used as the main injection amount.

  In FIG. 6, each diagram when the outside air temperature is higher than in the case of FIG. 4 is indicated by a solid line. For comparison, each diagram in FIG. 4 is also indicated by a one-dot chain line. (A) As shown in the figure, when the intake air temperature THIN is lower than the predetermined value THH, the intake air temperature THIN is higher than that in FIG. 4, and accordingly, the main injection amount Qm is maintained in order to maintain the same air-fuel ratio. Is reduced from the case of FIG. Then, the intake air temperature THIN reaches the predetermined value THH at a lower intake pressure PBH ′ than in the case of FIG. Therefore, the operation of the second fuel injection valve 33 is also started at a lower intake pressure PBH ′, and the operation of the second fuel injection valve 33 and the intake air cooling are started at an earlier timing in the acceleration state.

  Here, the advantage of setting the operation timing of the second fuel injection valve 33 with respect to the intake air temperature will be described. As described above, since the intake air is cooled by the outside air via the intercooler 13, the degree of cooling is reduced. Changes according to the outside temperature and the vehicle speed. Therefore, for example, it is not preferable to set the operation timing of the second fuel injection valve 33 with respect to the intake pressure or the supercharging pressure. This is because even if the intake pressure is constant, the intake air temperature changes according to the outside air temperature and the vehicle speed. On the other hand, if the operation timing of the second fuel injection valve 33 is set with respect to the intake air temperature as in this embodiment, the second fuel injection valve 33 can be operated when the intake air temperature THH is always constant, and the intake It directly meets the purpose of lowering the temperature and is more purposeful.

  Further, the installation position of the intake air temperature sensor 40 is preferably on the upstream side of the second fuel injection valve 33 as in the present embodiment. This is to prevent the intake air temperature sensor 40 from being affected by the intake air cooling by the second fuel injection valve 33.

  According to the map of FIG. 5, the auxiliary injection amount Qs increases as the intake air temperature THIN increases. Therefore, when the intake air temperature THIN rises as the boost pressure rises, the auxiliary injection amount Qs is increased by an amount corresponding to the increase degree of the intake air temperature THIN to increase the intake air cooling effect, and necessary and sufficient intake air cooling is executed. can do.

  In S105 of the routine shown in FIG. 2, the ECU 100 calculates the auxiliary injection amount Qs based on the basic injection amount Qt calculated in S101 and the set injection amount Qf stored in S108: Qs = Qt−Qf It may be calculated from

  As described above, according to the fuel injection control device for an internal combustion engine according to the present embodiment, when the intake air temperature exceeds a predetermined value, the second injection is performed together with the in-cylinder injection as the main injection by the first fuel injection valve. Since intake passage injection is performed as auxiliary injection by the fuel injection valve, the intake temperature can be lowered using the latent heat of vaporization of the auxiliary fuel before the intake is introduced into the in-cylinder combustion chamber, and the intake charging efficiency is increased. Can do. Further, the amount of fuel supplied into the in-cylinder combustion chamber (= main injection amount + auxiliary injection amount) can be increased by the increase in the intake air amount, and high output can be achieved. Furthermore, since the intake air temperature is lowered by the latent heat of vaporization of the auxiliary fuel, knock resistance can be improved.

  Further, at the time of high supercharging, the heat load on the intake valve 22 becomes high and thermal damage becomes a problem. However, according to this embodiment, the thermal damage can be prevented at the same time by fuel injection from the second fuel injection valve 33.

  As described above, since the second fuel injection valve is operated when the intake air temperature exceeds the predetermined value, the second fuel injection valve is more suitable than the technique disclosed in Patent Document 1, and has higher output and resistance. This is advantageous for achieving both knock properties. That is, in the technique of Patent Document 1, when the rotational speed of the internal combustion engine becomes higher than a predetermined level, the ratio of the fuel injection amount from the second fuel injection valve that performs port injection is automatically increased according to the map. However, in this case, when the rotational speed is higher than a predetermined level, even if the intake air temperature is sufficiently low, fuel injection is performed at a large injection amount ratio from the second fuel injection valve, resulting in overcooling of the intake air. In addition, there is a possibility that knocking may occur without sufficient fuel injection from the second fuel injection valve even if the intake air temperature is sufficiently high when the rotational speed is lower than a predetermined level. This embodiment can solve such a problem suitably.

  As can be seen from the above description, in the present embodiment, the intake air temperature sensor 40 constitutes intake air temperature detection means, and the ECU 100 constitutes injection valve control means.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, Various other embodiment can be taken. For example, the present invention is particularly effective for a supercharged engine such as the above-described embodiment where the intake air temperature is likely to rise, but the present invention is also applicable to a naturally aspirated engine. Moreover, although the example which performs stratified combustion and weak stratified combustion by the 1st fuel injection valve and the 2nd fuel injection valve was given in the above-mentioned embodiment, homogeneous combustion is performed by the 1st fuel injection valve and the 2nd fuel injection valve. There may be.

1 is a schematic system diagram showing a fuel injection control device for an internal combustion engine according to an embodiment of the present invention. It is a flowchart which shows the control routine of this embodiment. It is a colonnade map. It is a figure which shows the mode of the change of the intake air temperature, the air fuel ratio, and fuel injection amount accompanying the change of intake pressure. It is a calculation map of auxiliary injection amount. It is a figure similar to FIG. 4 when outside temperature rises.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 1st fuel injection valve 3 Turbocharger 9 Intake passage 13 Intercooler 15 Surge tank 22 Intake valve 23 Exhaust valve 24 Intake valve actuator 25 Exhaust valve actuator 28 In-cylinder combustion chamber 33 Second fuel injection valve 40 Intake temperature sensor 100 Electronic control unit (ECU)
THIN Intake temperature THH Predetermined value A of intake temperature A Blow-through area Qm Main injection quantity Qs Auxiliary injection quantity

Claims (7)

A first fuel injection valve for injecting fuel into the in-cylinder combustion chamber;
A second fuel injection valve for injecting fuel into the intake passage;
Intake air temperature detecting means for detecting intake air temperature at a predetermined position of the intake passage;
When the intake air temperature detected by the intake air temperature detecting means is below a predetermined value, fuel injection is executed only by the first fuel injection valve, and when the intake air temperature exceeds the predetermined value, fuel by the first fuel injection valve is executed. An internal combustion engine comprising: an injection valve control means for controlling the first fuel injection valve and the second fuel injection valve so as to execute fuel injection by the second fuel injection valve in conjunction with injection. Fuel injection control device.   The supercharger and an intercooler provided on the intake downstream side of the supercharger are further provided, and the second fuel injection valve is provided on the downstream side of the intercooler. A fuel injection control device for an internal combustion engine.   3. The fuel injection control device for an internal combustion engine according to claim 2, wherein the intake air temperature detecting means is provided on the downstream side of the intercooler and the upstream side of the second fuel injection valve.   Valve timing varying means for varying the valve timing of at least one of the intake valve and the exhaust valve, and when the intake air temperature exceeds the predetermined value, the overlap of the intake and exhaust valves is less than a predetermined basic overlap The fuel injection control device for an internal combustion engine according to any one of claims 1 to 3, further comprising valve timing control means for controlling the valve timing variable means.   5. The internal combustion engine according to claim 4, wherein the valve timing control means executes the control of the valve timing varying means when the intake air temperature exceeds the predetermined value and the engine operating state is in a predetermined blow-by region. Engine fuel injection control device.   The fuel injection control device for an internal combustion engine according to any one of claims 1 to 5, wherein a fuel injection amount injected from the second fuel injection valve is a function of the intake air temperature. The fuel injection amount of the first fuel injection valve is set to a value of a fuel injection amount immediately before the fuel injection amount of the first fuel injection valve when the intake air temperature exceeds the predetermined value. A fuel injection control device for an internal combustion engine according to any one of 1 to 6.

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