JP4765896B2 - Direct-injection spark ignition internal combustion engine - Google Patents

Description

  The present invention relates to a direct-injection spark-ignition internal combustion engine including a variable valve device that can change a lift amount of an intake valve.

Patent Document 1 discloses that in a direct-injection spark ignition internal combustion engine, the valve lift amount (and valve operating angle) of the intake valve is reduced at the start time and immediately after the start, and the valve timing of the intake valve is delayed so that the intake valve While the closing timing is fixed, the intake valve opening timing is delayed after the top dead center and after the exhaust valve closing timing. There has been disclosed a technique that aims to promote atomization of fuel by delaying the injection timing to near the bottom dead center and performing fuel injection at the maximum flow velocity.
JP 2005-201185 A

However, when the lift amount of the intake valve is small, the intake flow velocity increases, but the intake air enters the combustion chamber along the back of the intake valve, and travels along the wall of the combustion chamber as it is. At the same time, it has been found that the intake flow is difficult to be preserved because it quickly attenuates by colliding with the center and side of the upper surface of the combustion chamber.
For this reason, when the lift amount of the intake valve is small, the vaporization / diffusion of the injected fuel worsens, the in-cylinder mixture distribution becomes uneven, and these become more prominent when the fuel injection timing is delayed.

Therefore, for example, when the lift amount of the intake valve is controlled in accordance with the load in order to realize the possible non-throttle operation, if the lift amount of the intake valve becomes small in the low load region, the same reason as above Thus, the vaporization / diffusion of the injected fuel deteriorates, and the combustion stability deteriorates due to the deterioration of the homogeneity of the mixture.
In view of such a situation, an object of the present invention is to improve the homogeneity of an air-fuel mixture when the intake valve is in a low lift amount state in which intake flow is difficult to be preserved, and to ensure combustion stability.

The present invention relates to a direct injection spark ignition internal combustion engine including a fuel injection valve that directly injects fuel into a combustion chamber and a variable valve gear that can change a lift amount of an intake valve.
  The fuel injection timing is changed according to the lift amount of the intake valve, and in the high lift region, fuel injection is performed once after the exhaust top dead center, and in the low lift region, once before the exhaust top dead center. Fuel injection timing setting means for performing fuel injection and performing fuel injection twice before and after the exhaust top dead center in the middle lift amount region between the high lift amount region and the low lift amount region It is characterized by providing.

According to the present invention, the fuel injection timing is advanced before the exhaust top dead center when the intake air flow is a low lift amount where it is difficult to preserve, whereby the vaporization time until the ignition timing can be gained, and the homogeneity of the air-fuel mixture Can be improved. In the middle lift range, the fuel injection is divided into two times before and after exhaust top dead center, so that both combustion stability and smoke performance can be achieved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an internal combustion engine (engine) showing an embodiment of the present invention.
A combustion chamber 4 defined by the cylinder head 1, the cylinder block 2, and the piston 3 is connected to an intake port 6 through an intake valve 5 and is connected to an exhaust port 8 through an exhaust valve 7. The opening / closing timing of the intake valve 5 and the exhaust valve 7 can be controlled by the variable valve gears 9 and 10, respectively.

  As each of the variable valve gears 9, 10, for example, a valve timing variable device capable of variably controlling the valve timing of the intake / exhaust valves (center phase of the valve operating angle) by changing the rotation phase between the crankshaft and the camshaft. (VTC device) and a valve operating angle and valve lift continuously variable device (VEL device) capable of continuously variably controlling the valve operating angle (open period) and the valve lift amount are used in combination. In addition, a VTC device may be used in combination with a variable valve lift device (VVL device) that can switch the valve lift amount to a plurality of stages by switching cams, or an electromagnetic drive that drives intake / exhaust valves by an electromagnetic actuator. A valve device (EMV device) may be used. In any case, any variable valve operating device that can change the lift amount of the intake valve 5 may be used.

A fuel injection valve 11 and a spark plug 12 face the combustion chamber 4.
An electric throttle valve 14 is provided in the intake passage 13.
The operations of the variable valve gears 9 and 10, the fuel injection valve 11, the spark plug 12, and the electric throttle valve 14 are controlled by an engine control unit (ECU) 15.
The ECU 15 detects an engine speed Ne detected by a crank angle sensor (not shown), an accelerator opening APO detected by an accelerator opening sensor (not shown), and an air flow meter (not shown). Information such as the intake air amount Qa is input.

In the engine according to the present embodiment, the lift amount (and the open amount) of the intake valve 5 is proportionally proportional to the load while the electric throttle valve 14 is held substantially fully open (non-throttle state) at least under predetermined operating conditions. By controlling the period), the intake air amount is controlled, and the fuel corresponding to this is injected and supplied from the fuel injection valve 11, thereby realizing a substantially non-throttle operation.
When the lift amount of the intake valve 5 is controlled according to the load by the variable valve operating device 9, in particular by the combination of the VTC device and the VEL device, as shown in FIG. The characteristic (solid line in the figure) is the lift characteristic at high load. On the other hand, the smaller the load, the more the valve phase angle (and valve operating angle) is increased by the VEL device while the VTC device advances the central phase of the valve operating angle. The lift characteristic is reduced to a low load characteristic as shown by the dotted line in the figure.

3 and 4 show a reference example of the present invention . In FIG. 3, the vertical axis indicates the load (= lift amount of the intake valve), the horizontal axis indicates the fuel injection timing, and the range is satisfied. Matching is attached.
As the load decreases, the lift amount of the intake valve decreases, and the intake flow is less likely to be preserved for the reasons described above, so the vaporization and diffusion of the injected fuel deteriorates and the combustion stability σPi deteriorates. Therefore, it is necessary to advance the fuel injection timing to ensure time for the injected fuel to vaporize and diffuse. Therefore, there is a combustion stability limit (σPi limit) that the fuel injection timing needs to be advanced as the load (= lift amount) decreases, and the combustion stability (σPi) deteriorates on the retard side from this limit line. To do.

  In order to increase the vaporization / diffusion time, it is better to advance the fuel injection timing. However, when the load increases, the injection amount increases and a fuel injection of a certain amount or more is performed near the exhaust top dead center (TDC). As a result, the amount of adhesion to the piston increases and smoke is generated. Therefore, there is a certain restriction on the fuel injection in the vicinity of TDC, which is the smoke limit, and the smoke worsens on the high load side from this limit line. Note that smoke is also deteriorated when the injection timing is extremely delayed.

  In addition, the fuel injection timing is related to the exhaust valve closing timing. If the fuel injection timing is advanced too much, the injected fuel is discharged from the exhaust valve as it is and the HC deteriorates, so the time until the injected fuel reaches the exhaust valve ( In consideration of the distance), it is necessary to inject after the position slightly advanced from the exhaust valve closing timing. This is the HC limit determined by the relationship with the exhaust valve closing timing, and HC worsens on the advance side from this limit line.

  Therefore, if the engine has the σPi limit, the smoke limit, and the HC limit as shown in FIG. 3, the fuel injection timing is changed according to the load (= lift amount) along the σPi limit line, As the load (= lift amount) decreases, the fuel injection timing is advanced as indicated by the asterisk in the figure. In other words, fuel injection is performed after TDC in the high lift amount region, and fuel injection is performed before TDC in the low lift amount region.

A control flowchart in this case is shown in FIG.
In S1, load (= lift amount) is read.
In S2, a table (table data along the ☆ mark) as shown in FIG. 3 is referred to, and the fuel injection timing is set and controlled according to the load (= lift amount). This part corresponds to fuel injection timing setting means.

According to this example , as the lift amount of the intake valve becomes smaller, the fuel injection timing is advanced and / or in the region of the high lift amount, fuel injection is performed after exhaust top dead center, and the low lift amount In this region, by performing fuel injection before exhaust top dead center, it is possible to achieve both combustion stability (evaporation and diffusion promotion of injected fuel) and smoke limit (prevention of fuel adhesion to the piston).

It will be described implementation form of the present invention.
FIG. 5 shows a case where the smoke limit differs depending on the characteristics of the engine, and one-time injection near the exhaust top dead center (TDC) is not established.
Therefore, in the case of having the σPi limit, smoke limit, and HC limit as shown in FIG. 5 due to the characteristics of the engine, basically, fuel injection is performed along the σPi limit line according to the load (= lift amount). As the load is changed and the load (= lift amount) becomes smaller, the fuel injection timing is advanced as indicated by the asterisk in the figure. However, in the high lift region, after TDC, in the low lift region, after TDC Each fuel injection is performed once, while in the middle lift region between the high lift region and the low lift region, fuel injection is performed twice before and after the TDC (*). . In other words, in the middle lift region where single injection is difficult due to the smoke limit in the vicinity of TDC, the fuel injection is divided into two parts and injected in small amounts before and after TDC, so that the combustion stability (vaporization of injected fuel)・ Achieving both diffusion promotion and smoke performance (preventing fuel adhesion to the piston).

A control flowchart in this case is shown in FIG.
In S11, the load (= lift amount) is read.
In S12, referring to the table as shown in FIG. 5 (table data along the ☆ mark and data for double injection marked with ★), the fuel injection timing and the number of injections are determined according to the load (= lift amount). Set. This part corresponds to fuel injection timing setting means.

In S13, it is determined whether or not the number of injections = 2 (two injections). If NO, the process proceeds to S14 and one injection is performed. In the case of YES, it progresses to S15 and performs 2 times injection (split injection).
According to this embodiment, fuel injection is performed once after the exhaust top dead center in the region of the high lift amount, and fuel injection is performed once before exhaust top dead center in the region of the low lift amount. By injecting fuel twice before and after the exhaust top dead center in the middle lift amount region between the lift amount region and the low lift amount region, fuel injection near the top dead center Even when the fuel is prohibited from the smoke limit, both combustion stability (acceleration / diffusion promotion of injected fuel) and smoke performance (prevention of fuel adhesion to the piston) can be achieved.

In the on or more, with a variable valve device, according to the load, there has been described a case of controlling so as to reduce the lift amount of the intake valve as the low load, it is not necessarily limited to this, the intake valve It is generally applicable to those that control the lift amount.

Engine system diagram showing an embodiment of the present invention Explanatory drawing of lift amount control of intake valve by variable valve system The figure which shows an example of the optimal range of the fuel injection timing with respect to load (lift amount) Control flowchart of reference example The figure which shows the optimal range of the fuel injection timing with respect to load (lift amount) as embodiment of this invention Control flowchart of the embodiment of this

Explanation of symbols

4 Combustion chamber 5 Intake valve 7 Exhaust valve 9, 10 Variable valve device 11 Fuel injection valve 12 Spark plug 15 ECU

Claims (2)

In a direct injection spark ignition internal combustion engine comprising a fuel injection valve that directly injects fuel into a combustion chamber, and a variable valve gear that can change the lift amount of the intake valve,
The fuel injection timing is changed according to the lift amount of the intake valve, and in the high lift region, fuel injection is performed once after the exhaust top dead center, and in the low lift region, once before the exhaust top dead center. Fuel injection timing setting means for performing fuel injection and performing fuel injection twice before and after the exhaust top dead center in the middle lift amount region between the high lift amount region and the low lift amount region A direct-injection spark-ignition internal combustion engine characterized by comprising: 2. The direct injection spark ignition internal combustion engine according to claim 1, wherein the variable valve device is used to control the lift amount of the intake valve to be smaller as the load is lower, depending on the load.

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