JP2009243293A - Cylinder injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylinder injection type spark ignition internal combustion engine for efficiently strengthening a vertical swirl flow with injected fuel. <P>SOLUTION: The cylinder injection type spark ignition internal combustion engine is provided for strengthening a vertical swirl flow in a cylinder with the penetrating force of fuel injected from a fuel injection valve 1 which injects fuel directly into the cylinder. The fuel injection valve injects fuel at a piston position where a center height H of a cylinder space approximately corresponds to a cylinder bore diameter D. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  In homogeneous combustion in which a homogeneous mixture is formed in the cylinder and this homogeneous mixture is ignited and combusted at the ignition timing at the end of the compression stroke, the tumble flow formed in the cylinder by the intake air supplied into the cylinder until the latter half of the compression stroke. If it can be sustained, the tumble flow is crushed by the piston and turbulence can exist in the cylinder at the ignition timing, and good homogeneous combustion with a high combustion speed can be realized.

  In order to maintain the tumble flow until the latter half of the compression stroke, an intake flow control valve is arranged in the intake port, and the intake flow control valve supplies intake air along the upper wall of the intake port into the cylinder. An in-cylinder injection spark ignition internal combustion engine that forms a strong tumble flow has been proposed (see, for example, Patent Document 1).

JP 2005-180247 A JP 2003-113716 A JP 2005-61265 A JP 2005-120942 A JP 2005-61268 A

  In the above-described in-cylinder spark ignition internal combustion engine, when intake air is supplied into the cylinder along the upper wall of the intake port by the intake flow control valve, the intake port is throttled by the intake flow control valve. As a result, when the required intake air amount is relatively small, a strong tumble flow can be formed in the cylinder without any problem. However, when the required intake air amount is relatively large, the intake port is controlled by the intake air flow control valve. Since a shortage of intake may occur if the throttle valve is throttled, a strong tumble flow cannot be formed in the cylinder by the intake flow control valve.

  Even if such an intake flow control valve is not provided, in a cylinder injection type spark ignition internal combustion engine, for example, a fuel injection valve is arranged on the intake valve side substantially at the center of the cylinder or around the cylinder, and the exhaust valve of the cylinder bore If the fuel is injected toward the side, the tumble flow can be strengthened by the fuel injected along the traveling direction of the tumble flow. However, it is not possible to effectively strengthen the longitudinal swirl flow such as the tumble flow simply by injecting the fuel.

  Accordingly, an object of the present invention is to provide an in-cylinder injection spark ignition internal combustion engine that can effectively enhance the longitudinal swirl flow by the injected fuel.

  An in-cylinder injection spark ignition internal combustion engine according to claim 1 of the present invention includes a fuel injection valve that directly injects fuel into a cylinder, and the cylinder is driven by the penetration force of fuel injected from the fuel injection valve. In the in-cylinder injection spark ignition internal combustion engine that strengthens the vertical swirl flow in the cylinder, the fuel injection valve injects fuel at a piston position where the center height of the cylinder inner space substantially coincides with the cylinder bore diameter. .

  The direct injection spark ignition internal combustion engine according to claim 2 of the present invention is the direct injection spark ignition internal combustion engine according to claim 1, wherein when the required fuel amount is less than a first set amount, the fuel injection is performed. The valve injects a required amount of fuel at the piston position in the compression stroke, and when the required fuel amount is greater than or equal to the first set amount, the fuel injection valve injects a required amount of fuel at the piston position in the intake stroke. It is characterized by doing.

  A direct injection spark ignition internal combustion engine according to claim 3 of the present invention is the direct injection spark ignition internal combustion engine according to claim 2, wherein the required fuel amount is greater than the first set amount. At the above time, the fuel injection valve divides the required amount of fuel into two parts, injects one of the fuels divided into two at the piston position in the intake stroke, and the fuel divided into two at the piston position in the compression stroke The other of these is jetted.

  According to the in-cylinder injection spark ignition internal combustion engine of the first aspect of the present invention, the fuel injection valve injects fuel at a piston position where the center height of the cylinder interior space substantially coincides with the cylinder bore diameter. As a result, during fuel injection, the longitudinal swirling flow swirls in the cylinder in a substantially circular state, so that there is little energy loss, and the longitudinal swirling flow can be efficiently strengthened by the penetration force of the injected fuel. it can.

  According to the direct injection spark ignition internal combustion engine of claim 2 according to the present invention, in the direct injection spark ignition internal combustion engine of claim 1, when the required fuel amount is less than the first set amount, Because the amount of injected fuel is relatively small, the fuel injection valve injects fuel at the piston position in the compression stroke where the center height of the cylinder space substantially coincides with the cylinder bore diameter, and the longitudinal swirl flow is strengthened so much by the injected fuel. Even if this is not possible, the vertical swirl flow is reliably maintained until the latter half of the compression stroke. Further, when the required fuel amount is greater than or equal to the first set amount, the amount of injected fuel becomes relatively large, so that the fuel injection valve is located at the piston position in the intake stroke where the center height of the cylinder internal space substantially matches the cylinder bore diameter. Inject fuel and ensure that the longitudinal swirl flow is sufficiently strengthened by the injected fuel to ensure that it is sustained until the second half of the compression stroke, and that a relatively large amount of injected fuel is sufficiently homogeneously mixed for a relatively long time until the ignition timing. I have to.

  According to the direct injection spark ignition internal combustion engine according to claim 3 of the present invention, in the direct injection spark ignition internal combustion engine according to claim 2, the required fuel amount is greater than the first set amount. When the amount exceeds two preset amounts, the amount of injected fuel further increases, so it is difficult to inject all the fuel at the piston position in the intake stroke where the center height of the cylinder internal space substantially coincides with the cylinder bore diameter. Divides the required amount of fuel into two parts and injects one of the fuels divided into two at this piston position in the intake stroke, and at the piston position in the compression stroke where the center height of the cylinder internal space substantially coincides with the cylinder bore diameter. However, the other of the two divided fuels is injected, so that the longitudinal swirl flow can be strengthened very efficiently by the penetration force of each injected fuel.

  FIG. 1 is a schematic longitudinal sectional view showing an embodiment of a direct injection spark ignition internal combustion engine according to the present invention. In the figure, reference numeral 1 denotes a fuel injection valve arranged substantially at the center of the cylinder upper portion, and 2 denotes an ignition plug arranged in the vicinity of the fuel injection valve 1 (in this embodiment, on the exhaust valve side). Reference numeral 3 denotes a pair of intake ports that communicate with the inside of the cylinder via the intake valve 4, and reference numeral 5 denotes a pair of exhaust ports that communicate with the inside of the cylinder via the exhaust valve 6. 7 is a piston.

  In the in-cylinder spark ignition internal combustion engine, the intake air supplied from the intake port 3 into the cylinder in the intake stroke descends along the exhaust valve side of the cylinder bore and rises along the intake valve side of the cylinder bore. TB is formed. Since the in-cylinder injection spark ignition internal combustion engine is a two-valve intake type, two parallel airflows are formed in the cylinder at the beginning of the intake stroke. A single tumble flow TB swirling around a plane passing through the central axis and the middle of the two intake valves 6 (cross section in FIG. 1) as the central plane is obtained.

  A cavity 7a having a partial arc cross section parallel to the plane is formed on the top surface of the piston 7 in order to suppress the attenuation of the single tumble flow TB. However, by forming such a cavity 7a on the top surface of the piston 7, the tumble flow TB formed in the cylinder in the intake stroke by the intake air supplied by the intake port 3 that is not specially devised is It disappears easily in the first half of the compression stroke.

This in-cylinder injection spark ignition internal combustion engine forms a homogeneous mixture with fuel directly injected into the cylinder by the fuel injection valve 1 and performs homogeneous combustion. The air-fuel ratio of the homogeneous mixture is The lean air-fuel ratio is set to be leaner than the stoichiometric air-fuel ratio (preferably, the lean air-fuel ratio is set so that the amount of NO _x produced is suppressed), thereby suppressing fuel consumption. As a result, since the combustion tends to be slow, if the turbulence can be generated in the cylinder at the ignition timing by maintaining the tumble flow TB until the latter half of the compression stroke and crushing it by the piston, the combustion speed can be increased and good homogeneity can be achieved. Combustion can be realized. Of course, the air-fuel ratio of homogeneous combustion may be a stoichiometric air-fuel ratio or a rich air-fuel ratio. In this case as well, it is effective to increase the combustion speed.

  In the present embodiment, the fuel injection direction of the fuel injection valve 1 disposed substantially at the center of the upper part of the cylinder is directed to the lower part on the exhaust valve side of the cylinder bore, whereby the penetration force of the fuel injected by the fuel injection valve 1 Thus, the tumble flow in the cylinder is pushed in the traveling direction, and the tumble flow TB can be strengthened.

  However, simply injecting fuel into the tumble stream TB cannot effectively enhance the tumble stream TB. FIG. 2 is a graph showing changes in the strength of the tumble flow TB with respect to the piston position when the same amount of fuel is injected at the same injection pressure. The piston position is represented by the ratio between the center height H of the cylinder internal space and the cylinder bore diameter D. The center height H is a distance between the cylinder head and the piston top surface along the cylinder center axis. When this ratio is 1.0, it represents that the center height H of the cylinder internal space caused by the piston position is equal to the cylinder bore diameter D.

  As shown in FIG. 2, a difference occurs in the strength of the tumble flow depending on the ratio H / D described above, and the piston position when the ratio H / D is approximately 1.0, for example, the ratio H / D is 0.9. When the fuel is injected at a piston position between 1 and 1.1, the tumble flow TB can be enhanced well. This is because, at this piston position, the tumble flow TB turns in a substantially circular state as shown in FIG. When the piston position is low (ratio H / D> 1.1) and the tumble flow TB turns in a vertically long oval state, the tumble flow TB moves parallel to the cylinder bore (lowering and rising) and the cylinder bore Energy loss occurs due to friction. Further, when the piston position is high (ratio H / D <0.9), the bending radius when the tumble flow TB is deflected by the cylinder bore becomes small, and the energy loss at this time increases. Thus, the tumble flow TB when turning in a substantially circular state has the least energy loss, and at this time, the tumble flow TB can be effectively strengthened by the injected fuel.

  In the present embodiment, fuel injection is performed according to the flowchart shown in FIG. First, in step 101, the current required engine load L and the current required engine speed N are detected. Next, at step 102, it is determined whether or not the current requested engine operating state based on the requested engine load L and the requested engine speed N is the low rotation / low load region A in the map of FIG. When this determination is affirmative, the required fuel amount is less than the first set amount and the injected fuel amount is relatively small. Therefore, in step 103, the fuel injection valve 1 causes the center height of the cylinder space to increase during the compression stroke. The ratio H / D between the height H and the cylinder bore diameter D is between 0.9 and 1.1 (in terms of time, the time when the ratio H / D is 1.1 is before 0.9. ) The required amount of fuel is injected. Preferably, in the compression stroke, a required amount of fuel is injected at the center of the fuel injection period when the ratio H / D of the center height H of the cylinder internal space to the cylinder bore diameter D is 1.0.

  Thus, although the tumble flow TB can be efficiently enhanced by the injected fuel, the tumble flow TB may not be enhanced so much by the injected fuel because the required amount of fuel is relatively small. However, since the tumble flow TB is strengthened in the first half of the compression stroke, the tumble flow TB can be reliably maintained until the second half of the compression stroke. Thereby, in the low rotation low load region A, it is possible to realize good homogeneous combustion due to the turbulence generated by the tumble flow TB.

  On the other hand, when the determination in step 102 is negative, in step 104, whether the current required engine operating state based on the required engine load L and the required engine speed N is the middle-rotating load region B in the map of FIG. It is determined whether or not. When this determination is affirmative, the required fuel amount is equal to or greater than the first set amount, and the injected fuel amount is relatively large. Therefore, in step 105, the fuel injection valve 1 determines the center height of the cylinder space in the intake stroke. When the ratio H / D between the length H and the cylinder bore diameter D is between 0.9 and 1.1, a required amount of fuel is injected. Preferably, in the intake stroke, a necessary amount of fuel is injected when the ratio H / D of the center height H of the cylinder space to the cylinder bore diameter D is 1.0.

  In this way, the tumble flow TB can be efficiently strengthened by the injected fuel, and since the required fuel amount is relatively large, the tumble flow TB is sufficiently strengthened by the injected fuel and the tumble flow TB is reliably maintained until the latter half of the compression stroke. be able to. In addition, since a relatively large amount of injected fuel is injected in the intake stroke, it is sufficiently dispersed and homogenized in the cylinder using a sufficient time until the ignition timing by the enhanced tumble flow, and good homogeneity. An air-fuel mixture can be formed. Thereby, in the middle-rotation middle load region B, good homogeneous combustion can be realized by the turbulence generated by the tumble flow TB and the sufficiently homogenized homogeneous mixture.

  On the other hand, when the determination in step 104 is negative, the current required engine operating state based on the required engine load L and the required engine speed N is the high rotation / high load region C in the map of FIG. The amount is greater than or equal to the second set amount greater than the first set amount, and the amount of injected fuel is further increased. At this time, in a single fuel injection of the intake stroke, all the required amount is obtained when the ratio H / D of the center height H of the cylinder space to the cylinder bore diameter D is between 0.9 and 1.1. It becomes difficult to inject fuel.

  Thereby, the required amount of fuel is divided into two, and in step 106, the fuel injection valve 1 determines that the ratio H / D between the center height H of the cylinder internal space and the cylinder bore diameter D is 0.9 in the intake stroke. When it is between 1.1, one of the required amount of fuel divided into two is injected. Preferably, in the intake stroke, one of the required amount of fuel divided into two is divided with the ratio H / D of the center height H of the cylinder space and the cylinder bore diameter D being 1.0. Spray.

  Next, at step 107, the fuel injection valve 1 is operated when the ratio H / D between the center height H of the cylinder space and the cylinder bore diameter D is between 0.9 and 1.1 in the compression stroke. The other part of the divided amount of fuel is injected. Preferably, in the compression stroke, when the ratio H / D of the center height H of the cylinder space to the cylinder bore diameter D is 1.0, the other of the necessary amount of fuel divided into two is divided at the center of the fuel injection period. Spray.

  Thus, the tumble flow TB is efficiently strengthened by the fuel injected in the intake stroke and the compression stroke, and the tumble flow can be reliably maintained until the latter half of the compression stroke. Thereby, in the high rotation high load region C, good homogeneous combustion can be realized by the turbulence generated by the tumble flow.

  When dividing the required fuel amount into two, one fuel amount injected in the intake stroke and the other fuel amount injected in the compression stroke may be substantially equal, but one fuel amount is set to the second The remaining amount may be the other fuel. Thereby, a relatively large amount of fuel is injected in the intake stroke, and accordingly, the amount of fuel injected in the compression stroke can be reduced, which is advantageous for homogenization of the injected fuel.

  In step 108, it is determined whether or not the generated torque T has reached the allowable value T 'of the required torque in the current required engine operating state. The generated torque can be estimated based on, for example, crank angular acceleration at the initial stage of the explosion stroke of the specific cylinder. If the tumble flow TB is sufficiently strengthened and lasts until the latter half of the compression stroke, and strong turbulence can be generated in the cylinder at the ignition timing, good homogeneous combustion is realized, and the determination in step 108 is affirmed and there is no problem. . However, for example, when a deviation occurs in the fuel injection timing and the ratio H / D between the center height H of the cylinder space and the cylinder bore diameter D is not between 0.9 and 1.1, at least one If part of the fuel is injected, the tumble flow TB cannot be strengthened as intended, and the homogenization of the fuel may be insufficient. Denied.

  If the determination in step 108 is negative, it is determined in step 109 whether or not the difference ΔT between the allowable value T ′ and the generated torque T has increased compared to the previous time. At the beginning when the determination in step 108 is denied, this determination is denied, and in step 110, the current state of the flag F is maintained. Next, in step 112, it is determined whether or not the flag F is 0. Since the flag F is initially set to 0, the determination in step 112 is affirmed, and in step 113, the intake stroke and compression are determined. The fuel injection timing in the stroke is advanced by a set amount.

  Accordingly, fuel injection in the intake stroke and / or compression stroke is performed when the ratio H / D of the center height H of the cylinder interior space to the cylinder bore diameter D is between 0.9 and 1.1. If so, the generated torque T becomes equal to or greater than the allowable value T ′, and the determination in step 108 is affirmed.

  However, when the ratio H / D between the center height H of the cylinder space and the cylinder bore diameter D is not between 0.9 and 1.1, the amount of injected fuel in the intake stroke and / or the compression stroke is still If part of the fuel is being injected, the determination at step 108 is denied. At this time, if the determination at step 109 is negative, the fuel injection timing is improved by the advance angle of step 113. The fuel injection timing is further advanced by a set amount.

  Further, when the determination at step 108 is negative and the determination at step 109 is affirmative, the fuel injection timing is deteriorated by the advance angle of step 113, that is, the fuel injection is equal to the center height H of the in-cylinder space. It is considered that the amount of fuel injected when the ratio H / D with respect to the cylinder bore diameter D is not between 0.9 and 1.1 is increased. In step 111, the flag F is replaced from the current state. That is, when the flag F is 0, it is 1, and when the flag F is 1, it is 0.

  As a result, the flag F, which was currently 0, is replaced with 1, so the determination in step 112 is denied. In step 114, the fuel injection timings in the intake stroke and the compression stroke are both retarded by a set amount. . By repeating such processing, even if the fuel injection timing shifts, the ratio H / D between the center height H of the cylinder space and the cylinder bore diameter D is 0 in the intake stroke and / or the compression stroke. The fuel can be reliably injected when it is between .9 and 1.1, and the tumble flow TB can be enhanced well.

  The position of the fuel injection valve 1 is not limited to the approximate center of the cylinder upper portion. For example, the fuel injection valve 1 is arranged on the intake valve side around the cylinder upper portion, and is substantially horizontal (the horizontal direction is relative to the cylinder axis). The tumble flow TB can be strengthened by injecting fuel toward the exhaust valve side upper part of the cylinder bore in a direction along a vertical plane. Further, the penetration force of the fuel injected from the fuel injection valve 1 may be set so that the tip of the fuel after 1 ms from the start of the fuel injection reaches 60 mm or more so that the tumble flow TB can be surely strengthened. preferable.

  The shape of the injected fuel injected from the fuel injection valve 1 can be arbitrarily set, and may be, for example, a solid or hollow conical shape injected from a single injection hole. Moreover, it is good also as an approximately fan shape with comparatively thin thickness injected from a slit-shaped nozzle hole. Moreover, it is good also as a comparatively thin arc-shaped cross-section shape or convex line-shaped cross-section shape which makes the upper side and the exhaust valve side convex, by combining arc-shaped slit nozzle holes or a plurality of linear slit nozzle holes. Or it is good also as a column shape injected from a plurality of nozzle holes to each. In any case, it is sufficient that the injected fuel has a strong penetration force as described above to accelerate the tumble flow TB in the cylinder.

  The case where the tumble flow TB is formed in the cylinder has been described so far. However, the concept of the present invention is not limited to the tumble flow TB, and it descends along the intake valve side of the cylinder bore and moves toward the exhaust valve side. The present invention can be applied in the case where a longitudinal swirl flow including a reverse tumble flow rising along the cylinder is formed in the cylinder.

1 is a schematic longitudinal sectional view showing an embodiment of a direct injection spark ignition internal combustion engine according to the present invention. It is a graph which shows the change of the strength of the tumble flow with respect to the piston position when the same amount of fuel is injected at the same injection pressure. It is a flowchart for implementing the fuel injection of the cylinder injection type spark ignition internal combustion engine by this invention. It is a map which shows the area | region of the engine operation state defined by a request | requirement engine load and a request | requirement engine load.

Explanation of symbols

1 Fuel Injection Valve 2 Spark Plug 7 Piston TB Tumble Flow

Claims (3)

  In a cylinder injection spark ignition internal combustion engine comprising a fuel injection valve for directly injecting fuel into a cylinder, and strengthening a longitudinal swirling flow in the cylinder by a penetration force of the fuel injected from the fuel injection valve. The in-cylinder spark-ignition internal combustion engine, wherein the injection valve injects fuel at a piston position where the center height of the cylinder space substantially coincides with the cylinder bore diameter.   When the required fuel amount is less than the first set amount, the fuel injection valve injects the required amount of fuel at the piston position in the compression stroke, and when the required fuel amount is greater than or equal to the first set amount, the fuel injection valve The in-cylinder injection spark ignition internal combustion engine according to claim 1, wherein a required amount of fuel is injected at the piston position in the intake stroke.   When the required fuel amount is greater than or equal to the second set amount that is greater than the first set amount, the fuel injection valve divides the required amount of fuel into two, and one of the fuel divided into two at the piston position in the intake stroke 3. The direct injection spark ignition internal combustion engine according to claim 2, wherein the fuel is injected and the other fuel divided into two at the piston position in the compression stroke is injected.

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