JP2010037964A - Cylinder fuel injection spark ignition internal combustion engine - Google Patents

Abstract

A new method of forming an air-fuel mixture suitable for stratified combustion is provided.
A fuel injection valve 18 for injecting fuel into a combustion chamber and fuel spray spread angle adjusting means for adjusting the spread angle of fuel spray injected by the fuel injection valve are provided, and after the compression stroke starts, the combustion chamber 5 In a direct injection spark ignition internal combustion engine that closes the intake valve 6 after the internal gas starts to flow back into the intake passage 7 via the intake valve 6, the flow rate of the backflow gas flow is determined by the arrangement of the intake valve 6. When the combustion chamber 5 has a predetermined distribution corresponding to the stratified charge combustion, the fuel injection is performed with a smaller fuel spray spread angle toward the region with the fastest flow velocity during the compression stroke than in the homogeneous combustion. The fuel injection timing is set so that the injected fuel is deflected toward the spark plug 10 by the gas flow from the combustion chamber 5 toward the intake valve 6.
[Selection] Figure 4

Description

  The present invention relates to a direct injection spark ignition internal combustion engine.

  In a cylinder injection spark ignition internal combustion engine that performs homogeneous combustion with a fuel injection valve that injects fuel into the combustion chamber, the gas in the combustion chamber starts to flow back into the intake passage through the intake valve after the compression stroke starts. An in-cylinder spark ignition internal combustion engine that closes an intake valve later and injects fuel after the intake valve is closed is known (see Patent Document 1). According to this internal combustion engine, after the compression stroke starts, the pumping loss is reduced by closing the intake valve after the gas in the combustion chamber starts to flow back into the intake passage through the intake valve, and fuel consumption is suppressed. There is an effect that. Furthermore, by injecting fuel after the intake valve is closed, the temperature and pressure near the top dead center can be increased compared to the case of injecting fuel while the intake valve is open, and combustion occurs due to strong turbulence. There is also an advantage that speed is improved.

JP-A-9-287487

  However, in this internal combustion engine, since the time until ignition after fuel injection is short, a uniform air-fuel mixture that is optimal for homogeneous combustion cannot be obtained in the combustion chamber, and therefore unburned fuel increases and unburned fuel loss increases. There is a problem. There is also room for improvement in the formation of the air-fuel mixture even during stratified combustion.

  Therefore, the present invention is suitable for stratified combustion in an in-cylinder injection spark ignition internal combustion engine that closes the intake valve after gas in the combustion chamber starts to flow backward into the intake passage via the intake valve after the compression stroke starts. An object is to provide a new method of forming an air-fuel mixture.

  In order to solve the above-described problem, according to the first aspect of the present invention, a fuel injection valve that injects fuel into the combustion chamber and a fuel spray spread angle adjustment that adjusts the spread angle of the fuel spray injected by the fuel injection valve. And a switching operation between a homogeneous combustion mode in which a uniform mixture is formed in the combustion chamber and a stratified combustion mode in which a mixture is formed in the vicinity of the spark plug, and after the start of the compression stroke, In a cylinder-injection spark ignition internal combustion engine that closes the intake valve after the gas starts to flow back into the intake passage through the intake valve, the flow velocity of the backflowing gas flow has a predetermined distribution according to the arrangement of the intake valves. When stratified combustion is to be performed in the combustion chamber, fuel injection is performed with a smaller fuel spray spread angle toward the region with the fastest flow rate in the distribution during the compression stroke than in homogeneous combustion, and the injected fuel burns. The gas from the chamber to the intake valve Injection spark ignition internal combustion engine which sets the fuel injection timing to be deflected toward the ignition plug by the flow are provided.

  That is, according to the first aspect of the present invention, when stratified combustion is to be performed, during the compression stroke in which there is a gas flow from the combustion chamber toward the intake valve, that is, during the compression stroke and the intake valve is open or closed. By performing fuel injection immediately after the valve, the injected fuel can be deflected and an air-fuel mixture can be formed in the vicinity of the spark plug. The flow velocity of the backflowing gas flow has a predetermined flow velocity distribution that is determined by the arrangement of the intake valves, but fuel injection is performed with a smaller fuel spray spread angle toward the region of the fastest flow velocity in this distribution than in homogeneous combustion. Thus, a new method of forming an air-fuel mixture is provided in which the fuel spray is easily deflected and concentrated near the spark plug without being diffused throughout the combustion chamber.

  The spread angle of the fuel spray means an angle at which the fuel injected from the fuel injection valve spreads when the combustion chamber is viewed from the top in the direction of the central axis. Details will be described later with reference to FIG. The time when stratified combustion is to be performed is, for example, when the load is low or when the fuel consumption is low.

  Furthermore, according to this method, it is not necessary to have a cavity for guiding the injected fuel spray to the vicinity of the spark plug, which is conventionally used at the time of stratified combustion and formed on the top surface of the piston. In the case of forming a tumble flow during homogeneous combustion, compared to other pistons such as a piston having a flat top surface, the piston having this cavity interferes with the tumble flow and the tumble flow in the latter half of the compression stroke. It has the problem of being attenuated. However, this method eliminates the need to form a cavity on the top surface of the piston, so that the problem can be solved. As a result, problems such as attenuation of the tumble flow are eliminated, so that the combustion state is improved and fuel efficiency is improved.

  According to a second aspect of the present invention, in the first aspect of the present invention, a tumble control valve for controlling the generation of a tumble flow formed by the air sucked into the combustion chamber is disposed in the intake passage. An in-cylinder injection spark ignition internal combustion engine is provided in which the tumble flow controlled by the tumble control valve increases the flow velocity of the gas flow in the reverse direction.

  That is, in the invention described in claim 2, by controlling the tumble flow by the tumble flow control valve, the flow velocity of the backflowing gas flow is increased, and the injected fuel spray is more reliably deflected to the vicinity of the spark plug. The air-fuel mixture suitable for stratified combustion can be formed. Further, since the flow velocity of the gas flow that flows backward by the tumble flow by the tumble control valve is increased, the closing timing of the intake valve can be advanced compared to the case where the tumble flow is not used.

  According to a third aspect of the present invention, in the first aspect of the present invention, an injection pressure control means for controlling an injection pressure of the fuel injection valve is provided, and the higher the flow velocity of the backflowing gas flow, the higher the injection speed. An in-cylinder spark ignition internal combustion engine that increases pressure is provided.

  That is, according to the third aspect of the present invention, it is possible to inject fuel at an optimal injection pressure in order to form a good air-fuel mixture in the vicinity of the spark plug according to the flow velocity of the gas flow that flows backward. That is, when the fuel injection pressure from the fuel injection valve is small with respect to the flow rate of a certain reverse gas flow, that is, when the penetration force is small, the injected fuel spray is in front of the spark plug. As a result, the air-fuel mixture cannot be formed in the vicinity of the spark plug. On the other hand, when the injection pressure is large, that is, when the penetration force is large, the degree of deflection becomes small, and an air-fuel mixture cannot be formed in the vicinity of the spark plug and diffuses in the combustion chamber. Therefore, according to the present invention, it is possible to form a favorable air-fuel mixture in the vicinity of the spark plug.

  Further, according to the invention described in claim 4, in the invention described in any one of claims 1 to 3, a catalyst for purifying exhaust gas is arranged in the exhaust passage, and at the time of cold start, normal operation An in-cylinder injection type spark point internal combustion engine is provided in which the ignition timing is delayed and the stratified combustion is performed to raise the temperature of the catalyst.

  That is, in the invention according to claim 4, since the stratified combustion according to the present invention can retard the ignition timing more, it can also be used for raising the catalyst temperature during cold start.

  According to the invention described in each claim, there is a common effect that a new method of forming an air-fuel mixture suitable for stratified combustion can be provided.

  A cylinder injection spark ignition internal combustion engine according to the present invention will be described with reference to FIG. In FIG. 1, 1 is an engine body having four cylinders, for example, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an intake valve, 7 is an intake passage, 8 is an exhaust valve, Reference numeral 9 denotes an exhaust passage, and 10 denotes a spark plug. The intake passage 7 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to an air cleaner 14 via an intake duct 13. An air flow meter 15 for detecting the intake air flow rate and a throttle valve 17 driven by a step motor 16 are arranged in the intake duct 13. Further, an electrically controlled fuel injection valve 18 for injecting fuel into the combustion chamber 5 is disposed in the combustion chamber 5.

  Furthermore, the intake valve 6 and the exhaust valve 8 are respectively provided with variable valve mechanisms 19 and 20 that change their valve opening operations. Here, the valve opening operation is determined, for example, by one or more of the lift amount, the valve opening period (working angle), and the valve opening start timing, and any known mechanism can be used as the mechanism of this embodiment. It will not be described in detail.

  On the other hand, the exhaust passage 9 is connected to a small capacity three-way catalyst 22 via an exhaust branch pipe 21, and an air-fuel ratio sensor 23 for detecting the air-fuel ratio is attached to the exhaust passage upstream of the three-way catalyst 22. A water temperature sensor 24 for detecting the engine cooling water temperature is attached to the engine body 1.

  The electronic control unit (ECU) 40 is a digital computer and includes a ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45, An output port 46 is provided. The accelerator pedal 49 is connected to a load sensor 50 for detecting the depression amount of the accelerator pedal 49. Here, the depression amount of the accelerator pedal 49 represents a required load.

  Output signals from the air flow meter 15, the air-fuel ratio sensor 23, the water temperature sensor 24, and the load sensor 50 are input to the input port 45 via the corresponding AD converters 47. Further, the input port 45 is connected to a crank angle sensor 51 that generates an output pulse every time the crankshaft rotates, for example, 30 °. The CPU 44 calculates the engine speed based on the output pulse of the crank angle sensor 51.

  On the other hand, the output port 46 is connected to the spark plug 10, the step motor 16, the fuel injection valve 18, and the variable valve mechanisms 19 and 20 through corresponding drive circuits 48, which are output signals from the electronic control unit 40. Controlled based on

  The three-way catalyst 22 has an oxygen storage capacity, so that when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 22 is lean, it stores oxygen in the exhaust gas and flows into the three-way catalyst 22. When the air-fuel ratio of the exhaust gas is rich, the stored oxygen is released to oxidize and purify HC and CO contained in the exhaust gas.

  The in-cylinder spark-ignition internal combustion engine according to the present invention is in an operating state in which after the compression stroke starts, the gas in the combustion chamber 5 starts to flow backward into the intake passage 7 via the intake valve 6 and then closes the intake valve 6. Have That is, this has the conventional advantage that pumping loss is reduced and fuel consumption is suppressed. The internal combustion engine can be switched between a homogeneous combustion mode in which a uniform air-fuel mixture is formed in the combustion chamber 5 and a stratified combustion mode in which an air-fuel mixture is formed in the vicinity of the spark plug 10.

  First, homogeneous combustion will be described with reference to FIGS. This homogeneous combustion is of the type commonly performed. FIG. 2 is a schematic longitudinal sectional view of a direct injection spark ignition internal combustion engine showing fuel injection during homogeneous combustion. In this homogeneous combustion, the injected fuel is not affected by the gas flow in the combustion chamber 5 as will be described later. Therefore, the fuel spray 30 is not deflected but travels straight by the penetration force (penetration) at the time of injection. Finally, a uniform air-fuel mixture is formed in the combustion chamber 5.

  FIG. 3 schematically shows a view of the combustion chamber in FIG. 2 at the time of fuel injection as seen from the top in the section along the line II in the direction of the central axis. In FIG. 3, the angle at which the fuel spray 30 injected from the fuel injection valve 18 into the combustion chamber 5 spreads is referred to as a fuel spray spread angle θ.

  Next, stratified combustion, which is a feature of the present invention, will be described with reference to FIGS. FIG. 4 is a schematic longitudinal sectional view of a direct injection spark ignition internal combustion engine showing fuel injection during stratified combustion. In the fuel injection at the time of stratified combustion according to the present invention, the injected fuel is deflected toward the spark plug 10 by the gas flow from the combustion chamber 5 toward the intake valve 6 and stratified in the vicinity of the spark plug 10 as shown in FIG. Forms an air-fuel mixture suitable for combustion.

  That is, after the compression stroke starts, the piston 4 rises from the compression bottom dead center, and the gas in the combustion chamber 5 starts to flow back into the intake passage 7 via the intake valve 6. Thereby, at the time of fuel injection, a gas flow toward the intake valve 6 or the intake passage 7 is formed in the combustion chamber 5, and the injected fuel is caused by the gas flow as shown by the fuel spray 30 in FIG. It will be bent toward the spark plug 10. This gas flow is in the compression stroke and exists not only when the intake valve 6 is open but also immediately after the intake valve 6 is closed.

  FIG. 6 schematically shows a view of the combustion chamber as viewed from the top in the direction of the central axis along the line II in FIG. 2 during fuel injection, as in FIG. As shown in FIG. 6, the spread angle θ of the fuel spray at the time of fuel injection is set smaller than that at the time of homogeneous combustion. This is because fuel injection is concentrated toward the region 31 between the two intake valves 6. A region 31 indicates a region where the gas flows backward into the intake passages and has the highest flow velocity when the flow velocity distributions are compared in the cross section in FIG. This distribution tendency is considered to be the same in any other cross section of the combustion chamber, and is obtained by experiments or calculations in advance.

  Therefore, the fuel spray that is concentrated and injected toward the region 31 by reducing the fuel spray spread angle θ is greater in the degree of diffusion of the fuel spray 30 than when the fuel spray spread angle θ is increased. Therefore, it is possible to deflect the injected fuel to the spark plug 10 stably and reliably. That is, when the spread angle θ of the fuel spray is large, the fuel spray 30 spreads to other regions including the region 31 where the flow velocity of the gas flow is high. The flow rate difference is large. As a result, a part of the fuel spray 30 forms an air-fuel mixture in the vicinity of the spark plug 10, but the remaining fuel spray 30 diffuses into the combustion chamber 5 and an air-fuel mixture suitable for stratified combustion cannot be obtained. Accordingly, in the present invention, the fuel spray is concentrated toward the region 31 where the flow velocity of the backflowing gas flow is the fastest by reducing the spread angle θ of the fuel spray, thereby forming an air-fuel mixture suitable for stratified combustion. I am doing so.

  Note that the in-cylinder injection spark point internal combustion engine according to the present embodiment includes two intake valves 6. Therefore, the region 31 is a region between these intake valves, but other numbers of intake valves are used. In the in-cylinder injection spark point internal combustion engine provided, the position is different. Further, as means for changing the spread angle θ of the fuel spray, for example, a method for changing the fuel injection pressure, a method for changing the fuel spray by injecting air simultaneously with the fuel injection, and a shape of the nozzle hole are changed. There are methods.

  Next, a direct injection spark ignition internal combustion engine according to another embodiment of the present invention will be described with reference to FIG. The internal combustion engine shown in FIG. 7 differs from the internal combustion engine shown in FIG. 1 in that a tumble control valve (TCV) 26 driven by a step motor 25 is arranged in the intake branch pipe 11. The step motor 25 is connected to the output port 46 via a corresponding drive circuit 48 and is controlled based on an output signal from the electronic control unit 40. By controlling the opening and closing of the tumble control valve 26 using the step motor 25, it is possible to control the intake air flowing in the intake branch pipe 11, thereby generating the tumble flow in the combustion chamber 5 and its strength. Can be adjusted.

  FIG. 8 is a schematic longitudinal sectional view of a direct injection spark ignition internal combustion engine showing a state of fuel injection using the tumble flow 32 controlled by the tumble control valve 26. According to this embodiment, when stratified combustion is to be performed, the tumble flow is controlled by the tumble control valve 26 so that a part of the tumble flow 32 and the flow toward the top of the combustion chamber 5 passes through the region 31. By controlling the tumble flow 32 to pass through the region 31, the flow velocity of the backflowing gas flow increases, and the injected fuel spray 30 can be deflected more reliably to the vicinity of the spark plug 10, which is suitable for stratified combustion. An air-fuel mixture can be formed. Further, since the flow velocity of the gas flow flowing backward by the tumble flow 32 by the tumble control valve 26 is increased, the closing timing of the intake valve 6 can be advanced as compared with the case where the tumble flow 32 is not used.

  FIG. 9 shows the relationship between the closing timing of the intake valve 6 at a certain fuel injection timing and the flow velocity V of the gas flow flowing backward at that time in accordance with the opening degree of the tumble control valve 26. The abscissa represents the crank angle, and shows the interval between the compression bottom dead center (BDC) and the compression top dead center (TDC). The flow velocity V of the backflowing gas flow shown on the vertical axis indicates the flow velocity of the backflowing gas flow after being increased by the tumble flow 32, and the backflow is the minimum necessary for performing stratified combustion at a certain fuel injection timing. The gas flow velocity is indicated by VL.

  According to FIG. 9, at a certain fuel injection timing, in order to obtain a flow velocity VL of the reverse gas flow necessary for performing stratified combustion, when the tumble control valve 26 is fully closed (TCVC), the intake valve This indicates that when the tumble control valve 26 is fully open (TCVO), the closing timing of the intake valve must be after the crank angle CA2. The relationship shown in FIG. 9 and the flow velocity VL corresponding thereto are obtained in advance by experiment or calculation at each fuel injection timing, and are stored in the ROM 42.

  Based on the relationship shown in FIG. 9, the flow velocity VL of the backflowing gas flow that is the minimum necessary for performing stratified combustion controls the closing timing of the intake valve or the opening degree of the tumble control valve 26. It is possible to obtain by controlling or combining these.

  In each of the embodiments shown in FIGS. 1 and 7, the injection pressure of the fuel injected from the fuel injection valve 18 may be changed in accordance with the flow rate of the backflowing gas flow. This will be described with reference to FIG.

  FIG. 10 shows the relationship between the injection pressure P and the air-fuel ratio AF in the vicinity of the spark plug 10 at a flow rate of a certain reverse gas flow. At the flow velocity V of a certain reverse gas flow during stratified combustion, the minimum air-fuel ratio in the vicinity of the spark plug 10 capable of performing stratified combustion is AFL. Referring to FIG. 10, when the injection pressure P is smaller than P <b> 1, the injection pressure is low, the penetration force is weak, and the injected fuel spray 30 does not reach the spark plug 10. On the other hand, if the injection pressure P is greater than P2, the injection pressure is high and the penetration force is strong, and the injected fuel spray 30 is less deflected to the vicinity of the spark plug 10 and diffuses throughout the combustion chamber 5. Therefore, in these cases, an air-fuel mixture greater than the air-fuel ratio AFL required in the vicinity of the spark plug 10 for stratified combustion is not formed.

  As described above, when the injection pressure P1 is equal to or higher than the injection pressure P2, an air-fuel ratio mixture that is optimal for stratified combustion is formed in the vicinity of the spark plug 10. The values of the lower limit P1 and the upper limit P2 of the optimum injection pressure are obtained in advance by experiments or calculations according to the flow velocity V of the gas flow that flows backward, and are stored in the ROM 42.

1 is a schematic longitudinal sectional view of a direct injection spark ignition internal combustion engine according to the present invention. It is a schematic longitudinal cross-sectional view of the cylinder injection type spark ignition internal combustion engine which shows the fuel injection at the time of homogeneous combustion. FIG. 3 is a schematic cross-sectional view taken along line II in FIG. 2. It is a schematic longitudinal cross-sectional view of the cylinder injection type spark ignition internal combustion engine which shows the fuel injection at the time of stratified combustion. It is a schematic longitudinal cross-sectional view of the cylinder injection type spark ignition internal combustion engine which shows formation of the air-fuel | gaseous mixture suitable for stratified combustion. It is a schematic sectional drawing in alignment with line II of FIG. It is a schematic longitudinal cross-sectional view of another cylinder injection type spark ignition internal combustion engine by this invention. It is a schematic longitudinal cross-sectional view of the cylinder injection type spark ignition internal combustion engine which shows the fuel injection at the time of stratified combustion. It is a figure which shows the relationship between the valve closing timing of an intake valve, and the flow velocity V of the gas flow which flows backward. It is a figure which shows the relationship between an injection pressure and the air fuel ratio of the ignition plug vicinity.

Explanation of symbols

1 Engine Body 4 Piston 5 Combustion Chamber 6 Intake Valve 7 Intake Passage 10 Spark Plug 18 Fuel Injection Valve

Claims (4)

  Homogeneous combustion comprising a fuel injection valve for injecting fuel into the combustion chamber and a fuel spray spread angle adjusting means for adjusting the spread angle of the fuel spray injected by the fuel injection valve to form a uniform mixture in the combustion chamber This mode can be switched between the mode and the stratified combustion mode in which an air-fuel mixture is formed in the vicinity of the spark plug. After the compression stroke starts, the intake valve starts after the gas in the combustion chamber starts to flow back into the intake passage via the intake valve. In a cylinder injection spark ignition internal combustion engine that closes the valve, the flow velocity of the backflowing gas flow has a predetermined distribution according to the arrangement of the intake valves in the combustion chamber, and when stratified combustion is to be performed, Fuel injection is performed with a smaller fuel spray spread angle toward the region with the fastest flow rate in the distribution than in homogeneous combustion, and the injected fuel is deflected toward the spark plug by the gas flow from the combustion chamber toward the intake valve. Fuel injection timing The set injection spark ignition internal combustion engine.   A tumble control valve that controls the generation of a tumble flow formed by the air sucked into the combustion chamber is arranged in the intake passage, and the tumble flow controlled by the tumble control valve increases the flow velocity of the gas flow that flows backward. The in-cylinder injection type spark point internal combustion engine according to claim 1 to be made.   The in-cylinder injection type spark point internal combustion engine according to claim 1 or 2, further comprising injection pressure control means for controlling an injection pressure of the fuel injection valve, wherein the injection pressure is increased as the flow rate of the backflowing gas flow increases.   4. The catalyst according to claim 1, wherein a catalyst for purifying exhaust gas is disposed in the exhaust passage, and at the time of cold start, the ignition timing is delayed from that during normal operation and the stratified combustion is performed to raise the temperature of the catalyst. The in-cylinder injection spark point internal combustion engine as described in one.

Images