JP2009185687A - Direct-injection spark-ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve ignition stability by maintaining an air-fuel ratio around a spark plug in a combustible state over a comparatively long time range when performing start by stratified combustion. <P>SOLUTION: A multi-hole injection valve simultaneously injecting spray B1 directly directed to the spark plug 5 and spray B2 to B5 directed to a piston crown surface is used as a fuel injection valve 6. Compression stroke injection in starting is dividedly performed in a plurality of times. Thereby, the spray directly directed to the spark plug by second ignition or later reaches the spark plug between a period when the spray directly directed to the spark plug by first injection reaches the spark plug and a period when the spray directed to the piston crown surface by first injection is reflected by the piston crown surface and reaches the spark plug. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a direct-injection spark ignition internal combustion engine, and more particularly to fuel injection control at start-up.

In Patent Document 1, in a direct injection spark ignition type internal combustion engine, a fuel injection valve is provided on a side portion of a combustion chamber, and fuel is injected toward a piston crown surface in a compression stroke. The injected fuel is guided to the vicinity of the spark plug by the tumble flow rising along the inner wall of the cylinder so that the combustible air-fuel mixture is surely present in the vicinity of the spark plug at the ignition timing. Further, the fuel injection is divided into a plurality of times so that the tumble flow is not divided at a high load when the required amount of fuel increases.
JP 2004-162577 A

  However, when stratified combustion is performed at the time of start-up, the rotation rapidly increases, such as from the first explosion after cranking to fast idle, and under conditions with large fluctuations in rotation, only induction by the tumble flow can be performed around the spark plug. The air-fuel mixture distribution is unstable, and ignition stability and combustion stability may be deteriorated.

  Therefore, it is considered to improve ignition stability by using a fuel injection valve capable of simultaneously injecting spray directed directly to the spark plug and spray directed to the piston crown and igniting the spray directed directly to the spark plug. However, under extremely low rotation conditions such as at the time of starting, it is difficult to set the ignition timing because the spray speed is faster than the piston speed, and the spray immediately passes through the spark plug. There is room for improvement.

  In view of such a situation, the present invention can maintain the air-fuel ratio around the spark plug in a flammable state over a relatively long time range in order to enable a stable start by stratified combustion. It aims at making it possible to improve the property.

  Therefore, in the present invention, as the fuel injection valve, a fuel injection valve capable of simultaneously injecting spray directed directly toward the spark plug and spray directed toward the piston crown surface is used, and the compression stroke injection at the start is divided into a plurality of times. The configuration is as follows.

  According to the present invention, by split injection, the spray directly directed to the spark plug reaches the spark plug one after another, and further, the spray directed to the piston crown surface is reflected by the piston crown surface and reaches the spark plug. The air-fuel ratio around the spark plug can be maintained in a combustible state over a long time range, and the ignition stability and combustion stability are improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram of a direct injection spark ignition internal combustion engine showing an embodiment of the present invention.
In FIG. 1, a pent roof type combustion chamber 4 is formed by a cylinder head 1, a cylinder bore 2, and a piston 3, and a spark plug 5 is disposed at the center of the upper surface thereof. A fuel injection valve (injector) 6 for injecting fuel into the combustion chamber 4 is disposed obliquely downward on the side portion of the combustion chamber 4 (side portion on the intake side). C is a fuel injection valve central axis (axis).

As shown in FIG. 2, a plurality of injection holes A <b> 1 to A <b> 5 are formed on the front end surface (planar or hemispherical surface) of the fuel injection valve 6.
The plurality of nozzle holes A1 to A5 are formed by arranging circular nozzle holes in an inverted V shape on the front end surface of the fuel injection valve, and the remaining four nozzle holes A1 are arranged at the apex of the inverted V shape. It is divided into two nozzle holes A2 to A5.

The injection hole A1 is largely deflected upward with respect to the fuel injection valve central axis C, and injects spray (beam) B1 directed directly toward the spark plug 5 in a substantially horizontal direction.
The other nozzle holes A2 to A5 spray sprays B2 to B5 directed toward the crown surface of the piston 3 (specifically, the cavity of the piston crown surface) obliquely downward.

Here, although the total number of nozzle holes is five, this is not restrictive. Also, a plurality of nozzle holes that are directed directly toward the spark plug 5 may be provided.
The operation mode (combustion mode) of the internal combustion engine includes a homogeneous operation mode and a stratified operation mode.

  In the homogeneous operation mode, fuel injection of the fuel injection valve 6 is performed in the intake stroke, and a homogeneous air-fuel mixture is formed in the entire combustion chamber 4 by the ignition timing by the spark plug 5, so that the stoichiometric or lean air-fuel ratio ( A homogeneous combustion at A / F = 20-30) is performed.

  On the other hand, in the stratified operation mode, fuel injection of the fuel injection valve 6 is performed in the compression stroke, and a stratified air-fuel mixture is formed around the spark plug 5 so that the air-fuel ratio (lean fuel ratio) is extremely lean as a whole. Stratified combustion is performed at A / F = 30 to 40). At this time, the spray B1 directly directed to the spark plug 5 from the nozzle hole A1 is stratified around the spark plug, and the sprays B2 to B5 directed to the piston crown surface from the nozzle holes A2 to A5 It is reflected by the crown surface and is induced by the tumble flow in the combustion chamber to face the spark plug 5 and stratify around the spark plug 5.

  By the way, when stratified combustion is performed at the time of starting, in other words, when starting by stratified combustion and reducing the amount of HC emission at the time of starting, the air-fuel ratio around the spark plug should be kept in a combustible state for a relatively long time range. is required.

FIG. 3 is a diagram showing a change in the equivalent ratio (fuel / air ratio) around the spark plug in the case of a single compression stroke injection, and shows the case of low rotation, medium rotation, and high rotation.
Here, the engine speed from the first explosion to the fast idle is divided into low, medium and high, and low rotation (for example, 200 to 500 rpm), medium rotation (for example, 500 to 800 rpm), and high rotation (for example, 800 to 1200 rpm). Yes.

  The first steep peak in FIG. 3 is due to the spray B1 directly directed to the spark plug reaching the spark plug. At this time, the ignition limit (equivalent ratio not ignited below) φ1 is exceeded, and the combustible state (ignition) Possible state). The second large peak is caused by the sprays B2 to B5 directed to the piston crown surface being reflected by the piston crown surface and reaching the ignition plug. At this time, the ignition limit φ1 is exceeded and the flammable state (ignition state) Possible state).

  The rise time of the second peak increases with the rotation (= the width of the valley decreases with time) because the fuel pressure increases with the increase in rotation and the penetration of the spray increases. Due to increased liquidity.

  By the way, under extremely low rotation conditions such as when starting, (1) the spraying speed is higher than the piston speed, and the spray passes immediately through the spark plug, (2) the rotational fluctuation is large, (3) fuel pressure The air-fuel mixture distribution around the spark plug is not stable due to a large fluctuation. Therefore, it is difficult to ignite at the timing when the spray directly directed to the piston reaches the spark plug.

  Therefore, even if the ignition timing varies relatively, there is a peak due to the spray that reaches the spark plug by directing the spark plug of FIG. 3 and a peak due to the spray that reaches the spark plug reflected from the piston crown surface. Any one of the two peaks may be ignited, but the equivalence ratio between the two peaks cannot be ignited.

  In addition, the horizontal line of the double-ended arrow in FIG. 3 shows the discharge period (crank angle) at a constant discharge time of the spark plug at low rotation, medium rotation, and high rotation. The top horizontal line is The discharge period at low rotation, the middle horizontal line is the discharge period at medium rotation, and the bottom horizontal line is the discharge period at high rotation.

According to this, in the case of low rotation, if the discharge is performed between peaks, under the worst conditions, reliable ignition cannot be desired unless the discharge time is tripled.
In the case of medium rotation, if the discharge is performed between the peaks, under the worst conditions, reliable ignition cannot be desired unless the discharge time is doubled.

In the case of high rotation, even if a discharge is performed between the peaks, it can be ignited at the last minute in the normal discharge time.
Therefore, in the present invention, the fuel injection valve 6 capable of simultaneously injecting the spray directly directed to the spark plug and the spray directed to the piston crown surface is used while the compression stroke injection at the start is divided into a plurality of times. To do.

  More specifically, the split injection is performed when the spray directly directed to the ignition plug of the first injection reaches the ignition plug and the spray directed to the piston crown surface of the first injection is the piston crown surface. Is performed so that the spray directly directed to the ignition plugs of the second and subsequent injections reaches the spark plug between the time when the spark is reflected by the spark plug and reaches the spark plug.

  Further, the number of injections of the divided injection is set according to the engine speed. If the engine speed from the first explosion to the fast idle is divided into low, medium and high, it is 3 times at low speed and 2 times at medium speed. , Once at high rotation (no division).

FIG. 4 is a diagram showing a change in the equivalence ratio around the spark plug in the case of three injections at low rotation.
When the spray directly directed to the spark plug of the first injection reaches the spark plug, and when the spray directed to the piston crown of the first injection is reflected by the piston crown and reaches the spark plug During this period, when the spray directly directed to the ignition plug of the second injection and the spray directly directed to the ignition plug of the third injection reach the ignition plug, the equivalence ratio around the ignition plug is long. The flammable state is maintained and ignition is ensured.

FIG. 5 is a diagram showing a change in the equivalence ratio around the spark plug in the case of the two-time injection at the middle rotation.
When the spray directly directed to the spark plug of the first injection reaches the spark plug, and when the spray directed to the piston crown of the first injection is reflected by the piston crown and reaches the spark plug In the meantime, the spray directly directed to the spark plug of the second injection reaches the spark plug, so that the equivalence ratio around the spark plug is maintained in a combustible state for a long time, and ignition is ensured. In this case, the equivalence ratio temporarily becomes less than the ignition limit φ1, but the period is shorter than the discharge time and can be ignited even under the worst condition.

FIG. 6 is a flowchart of split injection at the start.
In S1, the internal combustion engine is cranked for starting.
In S2, a fuel pressure in a fuel accumulator pipe (common rail) that supplies high-pressure fuel to the fuel injection valve is detected, and it is determined whether or not the fuel pressure is equal to or higher than a predetermined value (injection permitted fuel pressure that allows compression stroke injection), and fuel pressure> predetermined When the value is reached, the process proceeds to S3.

  In S3, the engine speed N is detected, and compared with the threshold values NL, NM, NF, low rotation (N <NL) and medium rotation (NL <N <NM) in the range from initial explosion to fast idle. It is determined whether the engine speed is high (NM <N <NF) or more than the fast idle speed (N> NF).

  When the engine speed is low (N <NL), the process proceeds to S4 to determine whether or not injection can be performed three times. This is to limit the number of times of divided injection so that the fuel injection pulse width of each time of divided injection does not become smaller than a predetermined minimum pulse width.

  Specifically, at the time of stratification start, since a certain amount of fuel is injected, the fuel injection pulse width Pw is determined by the fuel pressure. Therefore, if the minimum pulse width is Pwmin, it is determined whether Pw / 3> Pwmin.

As a result, if three injections are possible (Pw / 3> Pwmin), the process proceeds to S5, and three injections (split injection) are performed in the compression stroke.
The fuel injection timing at the time of stratification start is set according to the engine speed together with the ignition timing and is advanced as the engine speed increases. The first injection timing is the same as this.

The injection timing for the second and subsequent injections is controlled by calculating the injection interval ΔCA at the crank angle based on the engine speed N by the following equation so that the injection interval becomes a certain fixed time (Tmin).
ΔCA [deg] = N × 360 ÷ 60 × Tmin
If the third injection is impossible (Pw / 3 <Pwmin), the process proceeds to S6 described later.

  In the case of medium rotation (NL <N <NM), the routine proceeds to S6, where it is determined whether or not two injections are possible. This is also to prevent the fuel injection pulse width of each divided injection from becoming smaller than the predetermined minimum pulse width.

Specifically, regarding the fuel injection pulse width Pw determined by the fuel pressure, if the minimum pulse width is Pwmin, it is determined whether Pw / 2> Pwmin.
As a result, if it is possible to inject twice (Pw / 2> Pwmin), the process proceeds to S7, and twice injection (split injection) is executed in the compression stroke.

If the second injection is impossible (Pw / 2 <Pwmin), the process proceeds to S8 described later.
In the case of high rotation (NM <N <NF), the process proceeds to S8, and a single injection in the compression stroke is executed. Therefore, split injection is not performed.

Therefore, after cranking, from the first explosion to the fast idle, as the engine speed increases, three injections → two injections → one injection are performed.
When the engine speed is equal to or higher than the fast idle speed (N> NF), the routine is terminated by the determination in S3 and the routine shifts to normal fast idle control.

  As described above, according to the present embodiment, the fuel injection valve 6 capable of simultaneously injecting the spray B1 directly directed to the spark plug and the sprays B2 to B5 directed to the piston crown surface is used, while the compression at the time of starting is performed. By performing the stroke injection divided into a plurality of times, in particular, when the spray directly directed to the ignition plug of the first injection reaches the ignition plug and the spray directed to the piston crown of the first injection By performing split injection so that the spray directly directed to the spark plug of the second and subsequent injections reaches the spark plug between the time when the spark is reflected by the piston crown and reaches the spark plug, the spark plug The equivalent ratio of the surroundings can be maintained in a combustible state over a long time range, and the ignition stability and the combustion stability can be improved.

  Further, according to the present embodiment, the number of injections of the divided injection is set according to the engine speed, and in particular, the engine speed from the first explosion to the fast idle is divided into low, medium and high, and the low speed The desired ignition stability can be ensured regardless of the change in the engine speed by setting three times at the time, twice at the middle speed, and once at the high speed (no division).

  Further, according to the present embodiment, the injection characteristics are deteriorated (pulse width-injection) by limiting the number of injections of the divided injection so that the fuel injection pulse width of each time of the divided injection is not smaller than the predetermined minimum pulse width. The ignition stability can be ensured while avoiding the use of the nonlinear region of the quantity characteristic.

  Further, according to the present embodiment, the fuel injection valve is a multi-hole injection valve having an injection hole A1 directly directed to at least one spark plug and injection holes A2 to A5 directed to at least one piston crown surface. Yes. By using such a multi-hole injection valve, since each directivity can be determined by each nozzle hole, desired directivity can be obtained in any direction.

  However, the application range of the present invention is not limited to the multi-hole injection valve. For example, it is possible to use a fuel injection valve that injects a hollow cone-shaped spray obliquely downward, and sprays the upper edge side directly toward the spark plug and the lower edge side toward the piston crown.

The block diagram of the direct-injection spark-ignition internal combustion engine which shows one Embodiment of this invention Arrangement of nozzle holes on the tip of the fuel injection valve The figure which shows the change of the equivalence ratio around a spark plug in the case of single injection The figure which shows the change of the equivalence ratio around the spark plug in the case of three times of injection at the time of low rotation The figure which shows the change of the equivalence ratio around a spark plug in the case of two injections at the time of medium rotation Flow chart of split injection at start-up

Explanation of symbols

1 Cylinder head 2 Cylinder bore 3 Piston 4 Combustion chamber 5 Spark plug 6 Fuel injection valve (multi-hole injection valve)
A1-A5 nozzle hole B1-B5 spray (beam)

Claims (6)

In a direct injection spark ignition internal combustion engine that includes a fuel injection valve at the side of the combustion chamber, injects fuel in the compression stroke at the start, and stratifies the air-fuel mixture in the vicinity of the spark plug to perform stratified combustion.
As the fuel injection valve, while using a fuel injection valve capable of simultaneously injecting spray directly directed to the spark plug and spray directed to the piston crown surface,
A direct-injection spark-ignition internal combustion engine characterized in that the compression stroke injection at the start is divided into a plurality of times.   The split injection is performed when the spray directly directed to the ignition plug of the first injection reaches the ignition plug and the spray directed to the piston crown surface of the first injection is reflected by the piston crown surface. The direct-injection spark-ignition internal combustion engine according to claim 1, characterized in that spraying directly directed to the ignition plug of the second and subsequent injections arrives at the ignition plug between the time when the ignition is reached. .   The direct injection spark ignition type internal combustion engine according to claim 1 or 2, wherein the number of times of the divided injection is set in accordance with an engine speed.   The number of injections of the divided injection is divided into low, medium, and high engine speeds from the first explosion to fast idle, and is 3 times at low speed, 2 times at medium speed, and 1 time at high speed. The direct-injection spark-ignition internal combustion engine according to claim 3.   5. The direct injection spark ignition type according to claim 3, wherein the number of injections of the divided injection is limited so that the fuel injection pulse width of each time of the divided injection does not become smaller than a predetermined minimum pulse width. Internal combustion engine.   The fuel injection valve is a multi-hole injection valve having an injection hole directly directed to at least one spark plug and an injection hole directed to at least one piston crown surface. 5. The direct injection spark ignition internal combustion engine according to any one of 5 above.

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