JP2016125453A - Fuel injection control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress accumulation of deposit on a first fuel injection valve injecting a liquid fuel into a cylinder, to the minimum in an internal combustion engine having the first fuel injection valve and a second fuel injection valve injecting a fuel different from the liquid fuel into an intake passage.SOLUTION: In switching from fuel injection by a second fuel injection valve to fuel injection by a first fuel injection valve in an internal combustion engine, the fuel is injected from the first fuel injection valve under a switching injection pressure adjusted to a pressure lower than a standard injection pressure by injection pressure adjustment means, before injection by the first fuel injection valve under the standard injection pressure determined on the basis of an operation state of the internal combustion engine is executed, and an injection time under the switching injection pressure in one combustion cycle, is determined to be longer than an injection time in a case when the fuel injection is executed under the standard injection pressure.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fuel injection control device for an internal combustion engine.

  In an internal combustion engine having an in-cylinder injector that directly injects fuel into the combustion chamber of the internal combustion engine and an intake port injector that injects fuel into the intake port of each cylinder, intake air is used to achieve predetermined combustion. If only the fuel injection from the port injector is performed, the in-cylinder injector continues to be exposed to high-temperature combustion gas without performing the fuel injection. As a result, the tip of the in-cylinder injector is maintained at a high temperature, and deposits are likely to be deposited in the injection hole. Thus, for example, in the technique disclosed in Patent Document 1, injection control is performed so that at least a part of the fuel to be injected is injected from the in-cylinder injector. As a result, the fuel flowing through the in-cylinder injector is expected to suppress the temperature rise at the tip of the injector.

JP 2006-132396 A

  As an internal combustion engine that uses two types of fuel and is provided with a fuel injection valve that injects each fuel, a fuel injection valve that injects liquid fuel into the cylinder, and a fuel that is different from the liquid fuel An internal combustion engine having a fuel injection valve that injects into an intake passage may be mentioned. In such an internal combustion engine, fuel injection corresponding to each fuel is performed from the corresponding fuel injection valve. Here, when the injection frequency of the fuel injected into the intake passage of the two types of fuel is higher than the injection frequency of the fuel injected into the cylinder, the fuel does not flow through the fuel injection valve injected into the cylinder. Since it is exposed to high-temperature combustion gas in a state, the temperature in the vicinity of the nozzle hole tends to be high. Moreover, even if there is no great difference in the injection frequency of both fuels, depending on the combustion state of the fuel in the combustion chamber, etc., if the fuel injection valve that injects into the cylinder is exposed to the combustion gas without flowing fuel, In some cases, the temperature in the vicinity of the injection hole of the fuel injection valve that injects the fuel into the cylinder may increase. In this way, when the vicinity of the injection hole of the fuel injection valve that injects into the cylinder is heated, switching is made so that the fuel injection by the fuel injection valve is performed, and deposits accumulate there, realizing a suitable fuel injection It becomes difficult to be done.

  The present invention has been made in view of the above problems, and includes an internal combustion engine having a fuel injection valve that injects liquid fuel into a cylinder and a fuel injection valve that injects fuel different from the liquid fuel into an intake passage. An object of the present invention is to provide a control device that realizes fuel injection for suppressing the accumulation of deposits in the former fuel injection valve as much as possible in an engine.

  In the present invention, in order to solve the above problems, when switching to fuel injection to a fuel injection valve that injects liquid fuel into a cylinder, fuel injection at an injection pressure determined based on the operating state of the internal combustion engine is performed. Before being performed, the fuel injection was performed at an injection pressure lower than the injection pressure so as to extend the injection period. As a result, it is expected that the temperature in the vicinity of the nozzle hole of the fuel injection valve is lowered to avoid deposit accumulation.

Specifically, the present invention provides a first fuel injection valve that injects a first fuel that is liquid fuel into a cylinder, and a second fuel injection valve that injects a second fuel different from the first fuel into an intake passage. A fuel injection control device for an internal combustion engine having a switching function for switching between fuel injection by the first fuel injection valve and fuel injection by the second fuel injection valve for fuel injection in the internal combustion engine And injection pressure adjusting means for adjusting the injection pressure of the first fuel by the first fuel injection valve. When the switching means switches from fuel injection by the second fuel injection valve to fuel injection by the first fuel injection valve, the standard injection pressure determined based on the operating state of the internal combustion engine Before the injection by the first fuel injection valve, fuel injection from the first fuel injection valve is performed at the switching injection pressure adjusted to a pressure lower than the standard injection pressure by the injection pressure adjusting means, and The injection period at the switching injection pressure in one combustion cycle is set longer than the injection period when fuel injection is performed at the standard injection pressure.

  The internal combustion engine is provided with a first fuel injection valve and a second fuel injection valve, and a first fuel that is liquid fuel is injected from the first fuel injection valve. Note that the second fuel injected from the second fuel injection valve may be either liquid fuel or gaseous fuel. Here, the switching of the fuel injection by the switching means is appropriately performed according to the purpose of the fuel injection in the internal combustion engine. For example, one of the first fuel and the second fuel is set to be used preferentially, and when the preferentially used fuel decreases or disappears, the remaining fuel The fuel injection may be switched so that is used. Alternatively, the fuel injection may be switched so that a suitable fuel is used in accordance with the operating state of the internal combustion engine or the like in order to improve fuel consumption or emission in the internal combustion engine. Furthermore, the fuel injection may be switched by the switching means as a result of selection of the fuel used by the user.

  Here, when switching from the fuel injection by the second fuel injection valve to the fuel injection by the first fuel injection valve is performed by the switching means, the fuel injection from the first fuel injection valve that has not been performed until then is performed. Fuel injection corresponding to the operating state is started. The injection pressure of the first fuel for realizing the fuel injection according to the operating state of the internal combustion engine is set as the standard injection pressure. The standard injection pressure is an injection pressure that is determined according to the operating state of the internal combustion engine. For example, the standard injection pressure is an injection pressure that is set to optimize the combustion efficiency of the first fuel in the internal combustion engine. Can do. And since the 1st fuel injection valve is comprised so that fuel injection is possible in a cylinder, even when the fuel injection by the 2nd fuel injection valve is performed, the injection hole vicinity of the 1st fuel injection valve Were exposed to the hot combustion gases in the cylinders. Furthermore, since the fuel did not flow through the nozzle hole of the first fuel injection valve, heat was not carried away to the fuel, so that the temperature in the vicinity of the nozzle hole was likely to rise. Therefore, when fuel injection at the standard injection pressure is started from the first fuel injection valve in a state where the temperature of the vicinity of the injection hole of the first fuel injection valve is increased according to switching, deposits are likely to be accumulated in the vicinity of the injection hole.

  Therefore, in the fuel injection control device for an internal combustion engine according to the present invention, when the fuel injection by the first fuel injection valve is switched, the standard injection is performed before the fuel injection by the first fuel injection valve at the standard injection pressure is performed. Fuel injection is performed at a switching injection pressure lower than the pressure. Since the switching injection pressure is lower than the standard injection pressure, the fuel injection amount per unit time injected from the nozzle hole of the first fuel injection valve at the time of fuel injection at the switching injection pressure is the standard injection pressure. Less than in the case of fuel injection. As a result, when performing the same amount of fuel injection, it is possible to set the injection period at the switching injection pressure in one combustion cycle longer than the injection period when the fuel injection is performed at the standard injection pressure. It becomes.

Therefore, at the time of fuel injection at the switching injection pressure, the first fuel can continue to flow through the nozzle hole for a longer time in one combustion cycle than fuel injection at the standard injection pressure. As a result, more heat in the vicinity of the nozzle hole of the first fuel injection valve can be easily transferred to the first fuel, the temperature in the vicinity of the nozzle hole can be quickly lowered, and deposit accumulation can be suppressed. . Also,
By transferring more heat to the first fuel, the temperature of the first fuel can be raised and the atomization in the cylinder can be promoted. In particular, since the injection pressure at the time of switching is lower than the standard injection pressure, the atomization of the first fuel becomes difficult to proceed due to a decrease in the injection pressure, but on the other hand, the atomization decreases due to the temperature of the first fuel rising. As a result, the deterioration of the combustion environment of the first fuel is suppressed.

  Here, the fuel injection control device may further include temperature estimation means for estimating a temperature in the vicinity of the injection hole of the first fuel injection valve. In this case, when the switching means performs switching from fuel injection by the second fuel injection valve to fuel injection by the first fuel injection valve, the temperature near the injection hole estimated by the temperature estimation means is a predetermined temperature. Is exceeded by the injection pressure adjusting means at the switching injection pressure adjusted to a pressure lower than the standard injection pressure when the temperature near the injection hole does not exceed the predetermined temperature. The fuel injection from the valve is performed and the injection period at the switching injection pressure in one combustion cycle is such that the fuel injection at the standard injection pressure is performed when the temperature near the injection hole does not exceed the predetermined temperature. It is set longer than the injection period when it is performed.

  By estimating the temperature in the vicinity of the injection hole, it is suitably determined whether or not deposits can be deposited in the vicinity of the injection hole of the first fuel injection valve when switching to fuel injection by the first fuel injection valve. be able to. That is, it can be considered that deposits can be deposited in the vicinity of the injection hole when the fuel injection by the first fuel injection valve at the standard injection pressure is performed in a state where the temperature in the vicinity of the injection hole exceeds the predetermined temperature. Therefore, when the temperature near the injection hole exceeds a predetermined temperature when switching to fuel injection by the first fuel injection valve, as described above, the first fuel injection valve performs fuel injection at the standard injection pressure. Prior to execution, fuel injection at the switching injection pressure is executed. Accordingly, deposit accumulation can be suppressed accurately, and when deposit accumulation does not occur, the fuel is injected at the standard injection pressure, so that the combustion of the first fuel in the internal combustion engine is in its operating state. It can be suitably realized according to.

  In the fuel injection control device, after the fuel injection by the first fuel injection valve at the switching injection pressure is started, the injection pressure adjustment is performed when the temperature near the injection hole reaches the predetermined temperature or less. The fuel injection from the first fuel injection valve may be performed at an injection pressure adjusted to the standard injection pressure by means. As a result, when it is determined that no accumulation of deposit occurs in the first fuel injection valve, it is possible to quickly shift to the fuel injection at the standard injection pressure, so that the combustion of the first fuel in the internal combustion engine depends on the operating state. And can be suitably realized.

  In the fuel injection control device described above, the second fuel may be a gaseous fuel, for example, CNG (compressed natural gas). Moreover, gasoline can be illustrated as a liquid fuel as a 1st fuel.

  According to the present invention, in an internal combustion engine having a fuel injection valve that injects liquid fuel into a cylinder and a fuel injection valve that injects fuel different from the liquid fuel into an intake passage, the deposit of the former fuel injection valve is reduced. It is possible to provide a control device that realizes fuel injection for suppressing deposition as much as possible.

It is a figure which shows schematic structure of the fuel-injection control apparatus of the internal combustion engine which concerns on this invention. FIG. 3 is a first flowchart regarding fuel injection switching control executed by the exhaust gas purification apparatus for an internal combustion engine shown in FIG. 1. FIG. It is a figure which shows transition of the injection pressure of the 1st fuel injection valve in the fuel injection switching control shown in FIG. 2, an injection period, and a nozzle vicinity temperature. FIG. 4 is a second flowchart regarding fuel injection switching control executed by the exhaust gas purification apparatus for an internal combustion engine shown in FIG. 1. It is a figure which shows transition of the injection pressure of the 1st fuel injection valve in the fuel injection switching control shown in FIG. 4, an injection period, and an injection hole vicinity temperature.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a spark ignition type internal combustion engine that can use CNG and liquid fuel (gasoline, alcohol fuel, etc.). The internal combustion engine 1 may be a compression ignition type internal combustion engine that can use CNG and light oil.

  An intake passage 3 and an exhaust passage 4 are connected to the internal combustion engine 1. The intake passage 3 is a passage for guiding fresh air (air) taken from the atmosphere to each cylinder 2. An air cleaner 30 is attached in the middle of the intake passage 3. The air cleaner 30 collects dust and dirt contained in the air. An air flow meter 31 is attached to the intake passage 3 downstream of the air cleaner 30. The air flow meter 31 outputs an electric signal correlated with the amount (mass) of air flowing through the intake passage 3. A throttle valve 32 is attached to the intake passage 3 downstream of the air flow meter 31. The throttle valve 32 changes the amount of air supplied to the internal combustion engine 1 by changing the cross-sectional area of the intake passage 3.

  Here, in the internal combustion engine 1, a first fuel injection valve 5 for injecting gasoline into the cylinder is provided for each cylinder. Each of the first fuel injection valves 5 is connected to a first delivery pipe 50. The first delivery pipe 50 is connected to the first fuel tank 52 via the first fuel passage 51. The first fuel tank 52 is a tank that stores gasoline that is liquid fuel. A fuel pump 53 for pumping up the gasoline stored in the first fuel tank 52 is attached in the middle of the first fuel passage 51. The fuel pump 53 is, for example, a turbine pump that is driven by an electric motor. The gasoline pumped up by the fuel pump 53 is supplied to the first delivery pipe 50 through the first fuel passage 51 and then distributed from the first delivery pipe 50 to the four first fuel injection valves 5. By the gasoline pumping by the fuel pump 53, the gasoline pressure in the first delivery pipe can be adjusted, so that the injection pressure of the first fuel injection valve 5 is adjusted.

  Further, the intake passage 3 downstream from the throttle valve 32 is branched into four branch pipes, and each branch pipe is connected to one cylinder 2. A second fuel injection valve 6 for injecting CNG into the branch pipe is attached to each branch pipe of the intake passage 3. The second fuel injection valve 6 is connected to the second delivery pipe 60. The second delivery pipe 60 is connected to the second fuel tank 62 via the second fuel passage 61. The second fuel tank 62 is connected to a filling port 63 attached to the vehicle body of the vehicle via an inlet pipe 64. The filling port 63 is opened when a filling nozzle arranged at a replenishment place (gas station or the like) is inserted, and introduces CNG supplied from the filling nozzle into the inlet pipe 64. CNG introduced from the filling port 63 to the inlet pipe 64 is stored in the second fuel tank 62.

The CNG stored in the second fuel tank 62 is supplied to the second delivery pipe 60 through the second fuel passage 61 and then distributed from the second delivery pipe 60 to the four second fuel injection valves 6. A shutoff valve 65 is disposed in the middle of the second fuel passage 61. The shutoff valve 65 is
When the fuel injection from the second fuel injection valve 6 is not performed, the valve is closed, and conversely, the fuel injection from the second fuel injection valve 6 is performed. Sometimes it opens. As the shut-off valve 65, for example, an electromagnetic valve device that opens when drive power is applied and closes when drive power is not applied can be used.

  A regulator 66 is disposed in the second fuel passage 61 downstream from the shutoff valve 65. The regulator 66 reduces the pressure of CNG supplied from the second fuel tank 62 to a preset pressure (set pressure). In other words, the regulator 66 has a passage sectional area of the second fuel passage 61 such that the fuel pressure in the second fuel passage 61 downstream from the regulator 66, that is, the injection pressure of the second fuel injection valve 6 becomes equal to the set pressure. It is a valve device that adjusts. As the regulator 66, for example, a mechanical valve device combining a diaphragm and a spring can be used. A pressure sensor 67 is attached to the second fuel tank 62. The pressure sensor 67 outputs an electrical signal correlated with the pressure in the second fuel tank 62.

  The exhaust passage 4 is provided with an exhaust purification device 40 for purifying the burned gas (exhaust gas) discharged from each cylinder 2 and a silencer. The exhaust purification device 40 includes, for example, a three-way catalyst, and the hydrocarbons in the exhaust when the air-fuel ratio of the exhaust flowing into the exhaust purification device 40 is in a predetermined range (for example, near the theoretical air-fuel ratio). Purifies (HC), carbon monoxide (CO), nitrogen oxides (NOx), etc. An A / F sensor 41 that outputs an electrical signal correlated with the air-fuel ratio is attached to the exhaust passage 4 upstream of the exhaust purification device 40.

An ECU (Electronic Control Unit) 7 is mounted on the internal combustion engine 1 configured as described above. The ECU 7 is an electronic control unit including a CPU, a ROM, a RAM, a backup RAM, and the like. In addition to the air flow meter 31, the A / F sensor 41, and the pressure sensor 57 described above, various sensors such as an accelerator position sensor 8, a crank position sensor 9, and a switching button 10 are electrically connected to the ECU 7. The accelerator position sensor 8 is a sensor that outputs an electrical signal correlated with the amount of operation of the accelerator pedal (accelerator opening). The crank position sensor 9 is a sensor that outputs an electrical signal correlated with the rotational position of the crankshaft of the internal combustion engine 1. The switch button 10 is a device that is provided in the vehicle interior and allows the driver to input a request for switching the fuel used.

  Various devices such as the first fuel injection valve 5, the second fuel injection valve 6, the throttle valve 32, the shutoff valve 55, and the fuel pump 63 are electrically connected to the ECU 7. The ECU 7 controls the various devices based on the output signals of the various sensors described above. For example, the ECU 7 specifies the operation state (for example, engine load, engine speed, etc.) of the internal combustion engine 1 based on the output signals of the various sensors described above, and performs control related to the combustion state of the air-fuel mixture based on the operation state. Parameters (eg, fuel injection amount, intake air amount, ignition timing, etc.) are obtained. Then, the ECU 7 controls the various devices according to the control parameter. Further, the ECU 7 switches the used fuel when the driver operates the switching button 10 (when a switching request is input).

In the internal combustion engine 1, it is possible to alternatively switch between gasoline and CNG as fuel to be used by operating the switching button 10 of the driver. Therefore, when gasoline is selected, fuel injection from the first fuel injection valve 5 is performed and fuel injection from the second fuel injection valve 6 is stopped. On the other hand, when CNG is selected, fuel injection from the second fuel injection valve 6 is performed and fuel injection from the first fuel injection valve 5 is stopped. Here, for example, since CNG as the fuel used is often cheaper than gasoline, the driver tries to use CNG as much as possible in order to reduce fuel costs. In such a case, when gasoline is used in the internal combustion engine 1 for some purpose, since the fuel injection by the first fuel injection valve 5 has been stopped until then, no fuel flows through the nozzle hole, and the vicinity of the nozzle hole There is a possibility that the temperature of Thus, when gasoline fuel injection is started in the state where the temperature in the vicinity of the injection hole of the first fuel injection valve 5 is increased, deposits may accumulate in the injection hole, and there is a risk of hindering combustion in the internal combustion engine 1. is there.

  Therefore, in the fuel injection control device for the internal combustion engine 1 according to the present invention, the fuel injection switching control shown in FIG. 2 is executed, thereby avoiding deposit accumulation in the injection hole of the first fuel injection valve 5. This fuel injection switching control is a control that is repeatedly executed at predetermined intervals by executing a predetermined control program in the ECU 7. FIG. 3 shows the injection pressure of the first fuel injection valve 5 when this fuel injection switching control is executed, the injection period in the combustion cycle, and the temperature transition in the vicinity of the injection hole of the first fuel injection valve 5. (A) to (c). Further, in FIG. 3, the transitions of the injection pressure, the injection period, and the temperature near the injection hole when the fuel injection switching control shown in FIG. 2 is performed are indicated by lines L1, L3, and L5. Each transition of the injection pressure, the injection period, and the temperature near the injection hole when the gasoline injection at the standard injection pressure described later is temporarily performed immediately after switching to the gasoline injection without performing the fuel injection switching control is represented by the line L2. , Lines L4 and L6.

  First, in S101, it is determined whether or not there is a switching request for switching the fuel used in the internal combustion engine 1 to gasoline, that is, a switching request for gasoline injection by the first fuel injection valve 5. As an example of the switching request, there is a mode in which gasoline is selected as the fuel to be used by operating the switching button 10 by the driver as described above. In this case, the switch request is issued by operating the switch button 10. As another example, in a state where the driver preferentially uses CNG, when the storage amount of CNG in the second fuel tank 62 decreases, the fuel to be used is automatically switched to gasoline. be able to. In this case, when the pressure in the second fuel tank 62 is detected by the pressure sensor 67 and the detected pressure falls below the threshold pressure, a request for switching from CNG to gasoline may be issued. If an affirmative determination is made in S101, the process proceeds to S102, and if a negative determination is made, this control is terminated.

  Next, in S102, the switching injection pressure P1 is calculated. The switching injection pressure P1 is an injection pressure set lower than a standard injection pressure P2 described later. When gasoline is used in the internal combustion engine 1 and there is no fear of deposit accumulation in the nozzle hole of the first fuel injection valve 5, the fuel injection condition of gasoline is predetermined according to the operating state of the internal combustion engine 1. According to standard conditions. That is, according to a predetermined standard condition relating to fuel injection, which is determined on the basis of parameters representing an operating state such as an engine load and an engine rotational speed in accordance with a predetermined purpose such as fuel efficiency and emission improvement of the internal combustion engine 1. Fuel injection of gasoline by the fuel injection valve 5 is performed. The predetermined standard conditions include the injection pressure of the first fuel injection valve 5, the injection period, the injection start timing, and the like related to the fuel pressure in the first delivery pipe 50. For example, in order to optimize the fuel efficiency of the internal combustion engine 1, the injection pressure, the injection timing, the injection start timing, etc. for completing the injection of gasoline of the injection amount calculated from the engine load at a predetermined crank angle timing are predetermined standards. It will be used as a condition. As for the predetermined standard condition, an optimized condition corresponding to the operating state of the internal combustion engine is calculated by experiment or the like according to a predetermined predetermined purpose (for example, for optimization of fuel consumption) What is necessary is just to memorize | store in ECU in the form of the control map which shows the correlation with the driving | running state of an engine, and predetermined standard conditions.

The injection pressure included in the predetermined condition determined according to the operating state of the internal combustion engine 1 corresponds to the standard injection pressure P2 (see line L2 in FIG. 3A). The switching injection pressure P1 is calculated as an injection pressure lower than the standard injection pressure P2 (see the line L1 in FIG. 3A). Specifically, the fuel injection amount Q is calculated according to the engine load of the internal combustion engine 1 at the time when the switching request is issued. Then, the longest crank angle period Tag that can be injected from the first fuel injection valve 5 in one combustion cycle in the internal combustion engine 1 is calculated. The longest crank angle period Tag is calculated in consideration of the fuel adhesion to the cylinder inner wall surface, the combustion stability of the injected fuel, the allowable range of emission deterioration, and the like. Then, in the longest injection period Tmax in which the injection from the first fuel injection valve 5 corresponding to the longest crank angle period Tag is possible, the injection pressure at which the fuel injection amount Q of gasoline can be injected is calculated as the switching injection pressure P1. Is done. As an example, the switching injection pressure P1 decreases as the longest injection period Tmax becomes longer.

  Since the switching injection pressure P1 is calculated based on the longest injection period Tmax as described above, it is considered to be the lowest injection pressure in the operating state of the internal combustion engine 1 at the time of calculation. On the other hand, since the standard injection pressure P2 is set for the purpose of improving fuel consumption in the internal combustion engine 1, it is generally considered that the standard injection pressure P2 is higher than the switching injection pressure P1, but some operating states of the internal combustion engine 1 In this case, the switching injection pressure P1 may be the same pressure value as the standard injection pressure P2. Even if the switching injection pressure P1 and the standard injection pressure P2 are the same in some operating states, if the switching injection pressure P1 is calculated to be lower than the standard injection pressure p2 in the other operating states, such The fuel injection control device of the embodiment also belongs to the category of the scope of the right of the present invention.

  When the process of S102 ends, the process proceeds to S103. In S103, the discharge pressure of the fuel pump 53 is adjusted so that the pressure in the first delivery pipe 50 becomes the switching injection pressure P1 calculated in S102, and the first fuel injection valve 5 is adjusted at the switching injection pressure P1. The gasoline injection from is executed. Thereafter, in S104, whether a predetermined time Δt has elapsed from the timing at which gasoline injection at the switching injection pressure P1 from the first fuel injection valve 5 is started according to the switching request (corresponding to the timing t1 in FIG. 3). It is determined whether or not.

  This predetermined time Δt is set on the basis that the gasoline flowing through the nozzle hole of the first fuel injection valve 5 takes away the heat of the first fuel injection valve 5 when gasoline is injected at the switching injection pressure P1. . The switching injection pressure P1 is the lowest pressure value among the injection pressures that can be taken in the current operating state of the internal combustion engine 1. Therefore, the injection period τ2 required to inject the amount of gasoline to be injected in one combustion cycle according to the engine load is longer than the injection period τ1 when the injection at the standard injection pressure P1 is performed (FIG. 3 (b)). That is, in the gasoline injection at the switching injection pressure P1, the gasoline flow rate through the nozzle hole is lower than that in the standard injection pressure P2, but the gasoline is flowing for a longer time. The amount of heat removed from the first fuel injection valve 5 by gasoline is governed mainly by the length of time the gasoline is flowing. Therefore, as shown in FIG. 3C, when the gasoline injection at the switching injection pressure P1 is performed, the injection of the first fuel injection valve 5 is compared with the case where the gasoline injection at the standard injection pressure is performed. The temperature in the vicinity of the hole is rapidly lowered, and the first fuel injection valve 5 is quickly brought into a state where deposit accumulation is unlikely to occur.

  In view of this, the predetermined time Δt takes into account the amount of heat removed in one combustion cycle during gasoline injection at the switching injection pressure P1, and makes the first fuel injection valve 5 difficult to deposit. It is calculated as the time required to lower the temperature of the first fuel injection valve to be achieved for placing. For example, the temperature of the first fuel injection valve 5 when the CNG injection by the second fuel injection valve 6 is performed in the internal combustion engine 1 is assumed in advance, and a necessary temperature decrease amount is set from the temperature. The predetermined time Δt can be calculated based on the amount of heat removed at the switching injection pressure P1. When following such a calculation method, the predetermined time Δt is calculated to be shorter as the amount of heat removed increases. Note that when the switching injection pressure P1 varies, it is considered that the amount of heat taken away also varies. Therefore, when calculating the predetermined time Δt, the correction may be sequentially performed in consideration of the variation of the switching injection pressure P1. As another method, the predetermined time Δt may be set to a fixed value in consideration of the minimum value of the amount of heat removed during gasoline injection at the assumed switching injection pressure P1. Note that the time point at which the predetermined time Δt has elapsed from the timing t1 is shown as the timing t2 in FIG.

  If an affirmative determination is made in S104, the process proceeds to S105, and if a negative determination is made, the processes after S102 are repeated. In S105, the gasoline injection at the standard injection pressure P2 is started when the predetermined time Δt has elapsed. Therefore, after timing t2 shown in FIG. 3, the injection pressure of the first fuel injection valve 5 is adjusted to the standard injection pressure P2 by the pump 53 in accordance with the operating state of the internal combustion engine 1, and then from the first fuel injection valve. The gasoline injection will be performed.

  As described above, according to this control, when switching from CNG injection to gasoline injection is performed in the internal combustion engine 1, gasoline injection at the switching injection pressure P1 is performed before gasoline injection at the standard injection pressure P1. As a result, the temperature of the first fuel injection valve 5 can be quickly reduced, and deposits can be prevented from depositing in the nozzle holes. In addition, when the gasoline is injected at the switching injection pressure P1, the atomization of the gasoline is difficult to proceed due to a decrease in the injection pressure, but the amount of heat received from the first fuel injection valve 5 of the gasoline increases. The impact on gasoline combustion in the cylinder is not considered significant.

  Next, a second embodiment of the fuel injection control device for the internal combustion engine 1 according to the present invention will be described with reference to FIGS. FIG. 4 is a flowchart of fuel injection switching control according to the second embodiment. As in the case of the first embodiment, the fuel injection switching control is a control that is repeatedly executed at predetermined intervals by executing a predetermined control program in the ECU 7. FIG. 5 shows the injection pressure of the first fuel injection valve 5 when this fuel injection switching control is executed, the injection period in the combustion cycle, and the temperature transition in the vicinity of the injection hole of the first fuel injection valve 5. (A) to (c). Further, in FIG. 5, the transitions of the injection pressure, the injection period, and the temperature near the injection hole when the fuel injection switching control shown in FIG. 4 is performed are indicated by lines L11, L13, and L15. The transition of the injection pressure, the injection period, and the temperature near the injection hole when gasoline injection at the standard injection pressure described later is performed immediately after switching to gasoline injection without performing the fuel injection switching control is represented by a line L12. , Line L14 and line L16.

  First, in S201, it is determined whether or not there has been a request for switching to gasoline injection by the first fuel injection valve 5 as in S101 described above. If an affirmative determination is made in S201, the process proceeds to S202, and if a negative determination is made, this control is terminated. Next, in S202, the nozzle hole vicinity temperature Tij of the first fuel injection valve 5 is estimated. The temperature near the injection hole Tij is a parameter related to gasoline combustion in the combustion chamber, based on the fact that the injection hole of the first fuel injection valve 5 is disposed in the cylinder 2 so that gasoline injection is possible. And when gasoline comes to flow through the nozzle hole of the first fuel injection valve 5 by the process of S205 described later, it is calculated in consideration of the amount of heat removed by the gasoline. Specifically, immediately after the request for switching, the engine load of the internal combustion engine 1, the engine water temperature of the internal combustion engine 1, and the period during which CNG injection was performed before switching to gasoline injection (ie, gasoline injection) The nozzle vicinity temperature Tij is calculated on the basis of the period during which no injection is performed. In addition, after the processing of S205 described later is performed, the injection hole vicinity temperature Tij is calculated from the injection hole vicinity temperature Tij immediately after the switching request in consideration of the amount of heat removed by gasoline. The temperature drop of the first fuel injection valve 5 due to the amount of heat taken away is as described in the first embodiment. When the process of S202 ends, the process proceeds to S203.

In S203, it is determined whether or not the injection hole vicinity temperature Tij estimated in S202 exceeds a predetermined temperature Tdepo. The predetermined temperature Tdepo is a threshold value of the temperature near the injection hole, where deposits can be accumulated in the injection hole when gasoline injection is performed in the first fuel injection valve 5 whose temperature has been increased. Therefore, the state in which the nozzle hole vicinity temperature Tij exceeds the predetermined temperature Tdepo means that deposits are likely to be deposited in the nozzle holes when gasoline injection is performed at the standard injection pressure P2. If a positive determination is made in S203, the process proceeds to S204, and if a negative determination is made, S2
Proceed to 06.

  In S204, the switching injection pressure P1 is calculated in the same manner as in S102 described above. In S205, the injection at the switching injection pressure P1 calculated in S204 is executed as in S103. Note that the timing at which the processing of S205 is performed for the first time in the fuel injection switching control corresponds to the timing t1 in FIG. By performing the process of S205, the temperature of the first fuel injection valve is efficiently reduced by the flow of gasoline. When the process of S205 ends, the process of S202 is performed again.

  Further, when the negative determination is made in S203, the temperature near the injection hole Tij of the first fuel injection valve 5 is not high enough to cause deposit accumulation at the time when the switching request is issued, and S205. There is a case where the nozzle hole vicinity temperature Tij is lowered by the above process. Therefore, in the former case, in response to the switching request, gasoline injection at the standard injection pressure P2 is started in S206. In the latter case, gasoline injection at the standard injection pressure P2 is started in S206 when the first fuel injection valve 5 has reached a state where deposit accumulation is unlikely to occur. The timing at which the injection hole vicinity temperature Tij is determined not to exceed the predetermined temperature Tdepo and the gasoline injection at the standard injection pressure P2 is started corresponds to the timing t3 shown in FIG.

  As described above, according to this control, when switching from CNG injection to gasoline injection is performed in the internal combustion engine 1, if the injection hole vicinity temperature Tij exceeds the predetermined temperature Tdepo, the gasoline injection at the standard injection pressure P1 is performed. Gasoline injection at the switching injection pressure P1 is performed before. As a result, the temperature of the first fuel injection valve 5 can be quickly reduced, and deposits can be prevented from depositing in the nozzle holes. In the case of the present embodiment, the gasoline injection at the switching injection pressure P1 is executed based on the estimated nozzle hole vicinity temperature Tij. Therefore, even when compared with the first embodiment, it is possible to accurately determine the timing at which the gasoline injection at the switching injection pressure P1 should be performed, and disadvantages due to the limitation of the gasoline injection at the standard injection pressure P2 (for example, When the standard injection pressure P2 is performed for the purpose of optimizing the fuel consumption of the internal combustion engine 1, deposit accumulation on the first fuel injection valve 5 can be avoided while reducing the fuel consumption and the like. .

1 internal combustion engine 2 cylinder 3 intake passage 4 exhaust passage 5 first fuel injection valve 6 second fuel injection valve 7 ECU
8 Accelerator position sensor 9 Crank position sensor 10 Switch button 50 First delivery pipe 53 Fuel pump 60 Second delivery pipe

Claims (4)

Fuel injection control for an internal combustion engine having a first fuel injection valve that injects a first fuel that is liquid fuel into a cylinder, and a second fuel injection valve that injects a second fuel different from the first fuel into an intake passage A device,
Switching means for switching between fuel injection by the first fuel injection valve and fuel injection by the second fuel injection valve for fuel injection in the internal combustion engine;
Injection pressure adjusting means for adjusting the injection pressure of the first fuel by the first fuel injection valve;
With
When the switching means switches from the fuel injection by the second fuel injection valve to the fuel injection by the first fuel injection valve, the first injection pressure at the standard injection pressure determined based on the operating state of the internal combustion engine. Prior to execution of injection by one fuel injection valve, fuel injection from the first fuel injection valve is performed at the switching injection pressure adjusted to a pressure lower than the standard injection pressure by the injection pressure adjusting means, and 1 The injection period at the switching injection pressure in the combustion cycle is set longer than the injection period when fuel injection is performed at the standard injection pressure.
A fuel injection control device for an internal combustion engine. Temperature estimation means for estimating the temperature in the vicinity of the nozzle hole of the first fuel injection valve,
When the switching means switches from fuel injection by the second fuel injection valve to fuel injection by the first fuel injection valve, the temperature near the injection hole estimated by the temperature estimation means exceeds a predetermined temperature. The injection pressure adjusting means causes the first fuel injection valve to switch from the first fuel injection valve at the switching injection pressure adjusted to a pressure lower than the standard injection pressure when the temperature near the injection hole does not exceed the predetermined temperature. Fuel injection was performed, and during the injection period at the switching injection pressure in one combustion cycle, fuel injection was performed at the standard injection pressure when the temperature near the injection hole did not exceed the predetermined temperature. If set longer than the injection period,
The fuel injection control device for an internal combustion engine according to claim 1. After the fuel injection by the first fuel injection valve at the switching injection pressure is started, when the temperature near the injection hole reaches the predetermined temperature or less, the injection pressure adjusting means adjusts the standard injection pressure. Fuel injection from the first fuel injection valve is performed at an injection pressure.
The fuel injection control device for an internal combustion engine according to claim 2. The second fuel is a gaseous fuel;
The fuel injection control device for an internal combustion engine according to any one of claims 1 to 3.

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