JP4618181B2 - Premixed compression self-ignition gasoline internal combustion engine - Google Patents

Description

  The present invention relates to a gasoline internal combustion engine that performs premixed compression self-ignition combustion.

  In recent years, an internal combustion engine that performs compression self-ignition combustion in an internal combustion engine that uses gasoline as fuel has been proposed. In general, compression self-ignition combustion forms a premixed gas and self-ignitions as piston compression progresses. Therefore, unlike combustion by flame propagation, the local combustion temperature is low and NOx is generated only in a very small amount. There is an advantage. On the other hand, in a homogeneous air-fuel mixture field, the entire area in the cylinder is ignited all at once, so if the air-fuel mixture is enriched as the load increases, the rate of pressure increase in the cylinder becomes too large, causing significant vibration and noise. There is a problem of becoming. Therefore, in order to expand the load range for performing the compression self-ignition combustion operation to the high load side, it is necessary to suppress the rate of pressure increase in the cylinder by making the ignition timing near the top dead center. .

  In Patent Document 1, a fuel injection valve is provided in the peripheral portion of the combustion chamber, the first concave chamber is provided at the end of the piston crown surface on the fuel injection valve side, and the axial direction of the fuel injection valve is relative to the first concave chamber. A second concave chamber adjacent to the first concave chamber and a fuel injection valve to inject fuel at different injection timings into the first concave chamber and the second concave chamber to form air-fuel mixtures having different concentrations to perform compression self-ignition combustion. An internal combustion engine to perform is disclosed.

JP 2002-195040 A

In Patent Document 1, fuel is injected twice from the fuel injection valve in one cycle to generate a rich air-fuel mixture in the first concave chamber and a lean air-fuel mixture in the second concave chamber. Since the rich air-fuel mixture is compressed and ignited in the first concave chamber, and the lean air-fuel mixture disposed in the adjacent second concave chamber is subjected to compression self-ignition combustion by the heat generation, the injection timing Is controlled twice in one cycle, the load on the control system is increased, and two-stage combustion is performed, so that the combustion tends to become unstable depending on the situation.
An object of the present invention is to provide a premixed compression self-ignition type gasoline internal combustion engine that can reduce the load of a control system and stably perform compression self-ignition combustion.

In order to achieve the above object, according to the first aspect of the present invention, a fuel injection valve that is disposed substantially in the center of the combustion chamber and injects fuel, and an intake air flow that promotes the intake air flow by narrowing the intake air passage that leads to the combustion chamber. The control valve controls the drive of the fuel injection valve so that the entire required fuel injection amount is injected at a time within a predetermined range from the late stage of the compression stroke of the engine to the compression top dead center. And control means for controlling to occupy a position for promoting flow and compressing and self-igniting the air-fuel mixture in the combustion chamber.
The invention according to claim 2 is characterized in that the predetermined range is a range from 40 ° before compression top dead center to compression top dead center, and in the invention according to claim 3, the charge injection valve is a multi-injection hole. It is characterized by.

  According to the present invention, the fuel injection valve is arranged substantially in the center of the combustion chamber, and the entire required fuel injection amount is injected at a time within a predetermined range from the latter half of the compression stroke of the engine to the compression top dead center, and the intake air flow By controlling the control valve to occupy a position that promotes intake air flow, fuel is injected from the center of the combustion chamber with respect to the intake air of the combustion chamber that is high pressure and the intake air flow is promoted, and the atomized fuel Because they are mixed at once, premixing is performed in a short period of time, and compression self-ignition combustion is likely to occur stably in the vicinity of compression top dead center, reducing problems due to early occurrence and delay of self-ignition combustion. it can. Further, since the fuel injection is not executed a plurality of times in a limited period before the compression top dead center, the burden on the control system can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 1 denotes an engine which is an internal combustion engine. In this engine 1, a combustion chamber 40 is formed by a cylinder 2b formed in a cylinder block 2a, a piston 16 that reciprocates up and down in the cylinder 1 and a cylinder head 2 provided in an upper portion of the cylinder block 2a. The piston 16 has a ball shape in which the crown surface is uniformly recessed. The valve mechanism of the engine 1 employs a DOHC 4-valve type. The intake side valve mechanism 50 includes an intake valve 7a for opening and closing an intake port 11 formed in the cylinder head 2 so as to communicate the intake passage 12 and the combustion chamber 40, and a rocker (not shown) at the upper end of the intake valve 7a. The intake camshaft 21 is formed with an intake cam 3a that abuts via an arm, and a known valve spring that biases the intake valve 7a in the valve closing direction. The exhaust-side valve mechanism 51 includes an exhaust valve 7b that opens and closes the exhaust port 17 formed in the cylinder head 2 so as to communicate with the combustion chamber 40, and an exhaust that abuts the upper end of the exhaust valve 7b via a rocker arm (not shown). The exhaust camshaft 22 is formed with a cam 3b, and a known valve spring that biases the exhaust valve 7b in the valve closing direction.

  Timing pulleys 4a and 4b are mounted on the ends of the intake camshaft 21 and the exhaust camshaft 22, respectively. These timing pulleys 4a and 4b are connected to the crankshaft 6 via a timing belt (not shown). The timing pulleys 4 a and 4 b and the camshafts 21 and 22 are rotationally driven as the crankshaft 6 rotates, and the intake and exhaust valves 7 a and 7 b are opened and closed in synchronization with the rotation of the engine 1 by the camshafts 21 and 22. Driven. In this embodiment, a tumble flow is basically generated in the combustion chamber 40 as an intake air flow.

  The cylinder head 2 is provided with a fuel injection valve 15 as fuel injection means for injecting fuel into the combustion chamber, and an ignition plug 19 as ignition means for facing the combustion chamber 40 and igniting the combustion chamber 40. The fuel injection valve 15 is arranged at the approximate center of the combustion chamber 40 when the cylinder block 2a is viewed from above in FIG. 1, and is a high-pressure injection nozzle that injects fuel at a high pressure. The fuel injection valve 15 is configured to be supplied with high-pressure fuel. A plurality of injection holes 15a provided at the tip of the fuel injection valve 15 face the combustion chamber 40 as shown in FIG. The number of the injection holes 15a of the fuel injection valve 15 is preferably at least 6 in consideration of the diffusibility of the fuel. In this embodiment, the fuel injection valve 15 is a multi-injection hole in which six injection holes 15a are formed at equal intervals in the circumferential direction, and is configured to inject fuel into the combustion chamber 40 radially. Yes.

  A throttle valve 14 and an intake flow control valve (hereinafter referred to as “FCV”) 37 that promotes intake flow by operating in a direction to narrow the intake flow path 12 are provided in the intake path 12. The throttle valve 14 is connected to an accelerator pedal 34 via a wire (not shown) or an electronic control mechanism, and its opening degree is adjusted according to the depression amount of the accelerator pedal 34.

  The FCV 37 is rotatably supported by a flange (not shown) in the intake passage 12 located upstream of the fuel injection valve 15, that is, between the fuel injection valve 15 and the throttle valve 14. The FCV 37 normally occupies a neutral position shown by a solid line in FIG. 3 and is rotated by the stepping motor 38 so that the upstream end 37a contacts the lower inner wall surface 12a of the intake passage 12 in FIG. Occupy position. The neutral position of the FCV 37 is a position substantially parallel to the intake flow path 12 where the flow passage area of the intake flow path 12 is the largest, and the operation position is a position where the tumble flow in the cylinder is strengthened.

  The engine 1 includes an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storing a control program and a control map, an engine control unit (hereinafter referred to as “CPU”), a timer counter, and the like. ECU ”) 31).

  The ECU 31 includes a fuel injection valve 15, an ignition plug 19, an engine speed sensor 32 serving as a rotation detection unit that detects the rotation state of the engine 1, and an opening detection unit that detects the opening of the throttle valve 14 serving as an engine load. A throttle opening sensor 33 and a stepping motor 38 are connected. The ECU 31 determines the intake, compression, explosion, and exhaust strokes of the engine 1 along with the ignition timing, fuel injection timing, combustion switching timing, and tumble strengthening timing by the spark plug 19 in accordance with information input from these sensors. ing.

  That is, the ROM stores in advance a map shown in FIG. 4 as combustion switching means obtained from the engine speed and the opening degree of the throttle valve 14, and when the engine speed and the throttle opening degree are in the region A, the compression self It is determined as an ignition combustion region, and when it is in region B, it is determined as a spark ignition combustion region. When the operating state of the engine 1 is in the compression self-ignition combustion region, the ECU 31 performs compression top dead center (TDC) from 40 ° (40 ° BTDC) before the compression top dead center, which is a predetermined range up to the compression top dead center. From the fuel injection valve 15 to the required fuel injection amount calculated based on the engine load and the rotational speed during the period up to 20 ° before compression top dead center (20 ° BTDC) to compression top dead center (TDC). The injection control is performed so that the injection is performed only once, and the stepping motor 38 is driven to move the FCV 37 to the operating position. In the case of the compression self-ignition combustion region, each part is controlled so that the spark plug 19 is in an inoperative state. When the operating state of the engine 1 is in the spark ignition combustion region, the ECU 31 does not drive the stepping motor 38 and places the FCV 37 at an intermediate position, performs the injection timing from the fuel injection valve 15 during the intake stroke, and sets the spark plug 19. Each part is controlled so that a spark is blown from.

  In such a configuration, intake air is introduced into the intake passage 12 from the air cleaner 13 as the piston 16 that reciprocates up and down in FIG. After the flow rate is adjusted according to the opening degree of the throttle valve 14 in the path 12, the air flows into the cylinder 2b through the intake port 11 when the intake valve 7a is opened.

  At this time, when the engine 1 is in the spark ignition combustion region, the fuel is injected into the combustion chamber 40 at a high pressure from the fuel injection valve 15 before the piston 1 starts to rise, that is, in the intake stroke. And compressed by being mixed with the intake air by the tumble flow generated by the intake air. When an ignition signal is applied to the spark plug 19, the air-fuel mixture is ignited by a spark and combustion by flame propagation is started. In the exhaust path 18 connected to the exhaust port 17, exhaust gas after combustion in the combustion chamber 40 is guided from the exhaust port 17 as the piston 16 rises when the exhaust valve 7 b is opened, It is discharged to the outside through the three-way catalyst 20 as a catalyst provided and a silencer (not shown).

  When the engine 1 is in the compression self-ignition combustion region, the stepping motor 38 is driven in the intake stroke, and the FCV 37 moves to the operating position. Then, as shown in FIG. 2, since the intake air is guided to the space between the downstream end 37b of the FCV 37 and the upper inner wall surface 12b, the flow velocity on the upper inner wall surface 12b side is increased. Will be strengthened.

  When the piston 1 moves up and enters the compression stroke and reaches 40 ° before compression top dead center, preferably 20 ° before compression top dead center, the ECU 31 drives the fuel injection valve 15 to burn high-pressure fuel from the injection hole 15a. It sprays in the chamber 40 only once. At this time, as shown in FIG. 2, since the injection holes 15a are minute and are formed at equal intervals in the circumferential direction, the fuel spray 36 is miniaturized and injected radially into the combustion chamber 40. The At this time, since the inside of the combustion chamber 40 is in the compression stroke, the internal pressure and temperature are high, and the tumble flow is promoted. Therefore, the fuel spray 36 that has been atomized by high-pressure injection and spreads radially from the center of the combustion chamber 40 and is mixed at once by a strong tumble flow, so that premixing is sufficiently performed and compression self-ignition combustion is performed at the compression top dead center Combustion is started in the vicinity. When the intake valve 7b is opened, the combustion gas is discharged from the exhaust port 17 through the exhaust path 18 to the outside through the three-way catalyst 20 and a silencer (not shown).

  In this way, the fuel injection valve 15 for injecting fuel at a high pressure is arranged in the approximate center of the combustion chamber 42, and is 40 ° before compression top dead center, preferably before compression top dead center, which is a predetermined range up to compression top dead center. Since the high-pressure fuel is injected at a time by driving at 20 ° so that the FCV 37 occupies a position where the intake air flow is promoted, the combustion chamber corresponds to the intake air of the combustion chamber 40 at a high pressure and the intake air flow is promoted Since the atomized fuel spray 36 injected at a high pressure from the center of 40 is mixed all at once, premixing is performed all at once, and compression self-ignition combustion is likely to occur stably near the compression top dead center. Problems due to early occurrence or delay of combustion can be reduced. Further, since the fuel injection is not executed a plurality of times in a limited period before the compression top dead center TDC, the burden on the ECU 31 can be reduced.

  In the present embodiment, the injection pressure from the fuel injection valve 15 is increased because atomization of the fuel spray 36 is effective in order to accelerate the vaporization of the fuel spray 36 and to facilitate mixing with the intake air in the combustion chamber 40. The reason is that, as the injection pressure is increased from the relationship between the injection pressure and the atomization, the atomization is further promoted, so that the high-pressure injection is effective in reducing the mixing time. In general, the relationship between the injection pressure and the atomization of spray (Sauta) has a characteristic that the injection pressure becomes higher and the injection hole becomes smaller as shown in FIG. According to the inventor's consideration, the injection pressure is desirably 20 MPa or more.

  The injection timing in the compression self-ignition combustion region is preferably after the timing at which the engine 1 is not damaged even if ignition occurs simultaneously with the start of injection, and the injection starts after 40 to 20 ° BTDC and completes before TDC. I made it. In addition, in order to shorten the mixing time of the fuel spray 36 in the compression self-ignition combustion region, the necessary in-cylinder flow requires in-cylinder flow energy equivalent to 6 or more in the case of tumble, so the FCV 37 is driven. The tumble flow was promoted.

  The relationship between the mixing time of the fuel spray 36 and the swirl ratio or tumble ratio will be described. The swirl ratio or tumble ratio represents the rotation ratio of in-cylinder air (assumed to be a rigid body) with respect to one rotation of the engine. Therefore, when mixing the fuel spray 36 is considered, it is considered that the minimum condition is that the swirl rotates at least once. In this case, considering that the period from the start of injection to TDC is only 30 ° CA, 360 is considered. A swirl ratio corresponding to ° / 30 ° = 12 is required. However, in the case of tumble, since the rigid vortex radius is reduced in the compression stroke, the tumble rotation speed at the time of fuel injection is improved, and the required value is about halved, so the required tumble ratio is 6. The normal engine tumble ratio is about 0.5 to 2.0. The tumble ratio and swirl ratio here use values calculated from the rotational energy of the in-cylinder air at the end of the intake stroke.

  When the fuel injection valve 15 is made to have a plurality of injection holes, the fuel spray 36 is dispersed, so that the mixing becomes easy and the required tumble ratio can be reduced. Furthermore, since the atomization of the spray is promoted as the injection hole 15a is made smaller, the mixing time is shortened. On the other hand, since the flow rate is reduced, it is difficult to ensure the maximum fuel flow rate. The total flow rate can be secured because the number of nozzles is increased at the same time as the caliber.

  Based on such considerations, the present inventor considered that it is desirable to set the number and size of the nozzle holes 15a, the injection pressure and injection timing of the fuel injection valve 15, and the operation of the FCV 37 as described above. In this embodiment, the intake flow is reinforced with the FCV 37 as a tumble flow, but it goes without saying that the intake flow is a swirl flow, and if the FCV 37 is rotated 90 degrees in the circumferential direction from the state shown in FIG. Good.

1 is a diagram showing a schematic configuration of an internal combustion engine according to an embodiment of the present invention. It is an enlarged view which shows the injection hole of the fuel injection valve seen from the combustion chamber side, and the state of spray. It is an enlarged view showing the configuration of the intake flow control valve, the positional relationship with respect to the intake flow path, and the flow of intake air. It is a map which shows the switching characteristic of a compression self-ignition combustion area | region and a spark ignition combustion area | region. It is a diagram which shows the relationship between an injection pressure and spray atomization.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 12 Intake flow path 15 Fuel injection valve 15a Injection hole 31 Control means 37 Intake flow control valve 39 Intake control apparatus 40 Combustion chamber

Claims (3)

A fuel injection valve that is disposed substantially in the center of the combustion chamber and injects fuel;
An intake flow control valve that promotes intake flow by narrowing the intake flow path leading to the combustion chamber;
The drive of the fuel injection valve is controlled so that the entire required fuel injection amount is injected at a time within a predetermined range from the late stage of the compression stroke of the engine to the compression top dead center, and the intake flow control valve controls the intake flow. A premixed compression self-ignition type gasoline internal combustion engine comprising control means for controlling the fuel gas in the combustion chamber to occupy a position to be promoted to compress and self-ignite. The premixed compression self-ignition gasoline internal combustion engine according to claim 1,
The premixed compression self-ignition gasoline internal combustion engine, wherein the predetermined range is a range from 40 ° before compression top dead center to compression top dead center. The premixed compression self-ignition gasoline internal combustion engine according to claim 1 or 2,
2. A premixed compression self-ignition gasoline internal combustion engine characterized in that the fuel injection valve has multiple injection holes.

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