Ignition control for fuel direct injection type engine

Details Ignition control for fuel direct injection type engine Ignition control for fuel direct injection type engine

1998-09-11

2001-01-23

Solis, Erick (Department: 3747)

Internal-combustion engines

Combustion chamber means having fuel injection only

Combustible mixture stratification means

C123S305000, C123S607000

Reexamination Certificate

active

06176216

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Patent Applications No. 9-246276 filed on Sep. 11, 1997 and No. 10-235591 filed on Aug. 21, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ignition control for a direct fuel injection type internal combustion engine in which gasoline fuel is injected directly into a combustion chamber.
2. Related Art
In a direct fuel injection type internal combustion engine, air-fuel mixture of a very lean air-fuel ratio is burned in combustion chambers for low fuel consumption and low exhaust emission. This lean air-fuel mixture is less ignitable in comparison with an air-fuel mixture of stoichiometric air-fuel ratio by which conventional engines are operated. Therefore, the direct fuel injection type engine is designed to have an improved fuel injection system and improved piston configuration so that fuel-rich region in a generally stratified lean air-fuel mixture is formed near a spark generating area of a spark plug for better ignitability. For instance, as shown in
FIG. 8
, the fuel-rich mixture formed by air and fuel injected directly from a fuel injector
18
into the combustion chamber is guided toward the spark generating area of a spark plug
17
along a top recess
21
of a piston
20
, i.e., from T
1
to T
3
through T
2
in the combustion chamber. The spark plug
17
is activated to generate an electric discharge spark and ignite the fuel-rich mixture first when the fuel-rich mixture arrives at T
3
. The combustion of the fuel-rich mixture propagates to the fuel-lean mixture existing around the fuel-rich mixture.
However, timing of fuel injection, timing of opening and closing of an intake valve, flow speed of the fuel-rich mixture in the combustion chamber and the like vary from time to time and from engine to engine. Thus, as shown in
FIG. 9
, time of arrival of the fuel-rich mixture at the spark generating area of the spark plug
17
varies between time t
1
and time t
2
. If the arrival time is later than the time the spark plug
17
generates the electric discharge spark, the fuel-rich mixture will not be ignited resulting in misfire of the stratified air-fuel mixture in the engine. The electric discharge period of the spark plug
17
may be lengthened to ignite even the late-arriving fuel-rich mixture. This will, however, increase the size and weight of the ignition device.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved ignition control which ensures igniting a stratified air-fuel mixture in a fuel direct injection type internal combustion engine.
According to the present invention, a switching device for an ignition coil is turned on and off repeatedly so that the ignition coil repeats its electric discharging a multiple of times for generating multiple sparks from a spark plug in each ignition cycle of an internal combustion engine. These multiple sparks ignite a fuel-rich mixture in a generally lean stratified air-fuel mixture even in the case that a arrival of fuel-rich mixture at the spark generating area of the spark plug is delayed after the first spark.
The multiple sparks may disadvantageously promote wear of an electrodes of the sparkplug and heating of an ignition device. Therefore, multiple discharging is preferably limited to a necessary minimum. That is, multiple discharging is limited to only a predetermined engine operating region where the arrival timing of the fuel-rich mixture is likely to vary. The multiple discharging is disabled in the other engine operating regions where the arrival time of the fuel-rich mixture does not vary so much.
Specifically, the multiple discharging may be limited to only a relatively low engine speed region. In a high engine speed region, the period of ignition cycle is short and the variation in arrival time of the fuel-rich mixture is small. Therefore, the fuel-rich mixture is ignited by a single spark in the high engine speed region. Because the ignition device operates more frequently in the high engine speed region, the ignition device will generate more heat than in the low engine speed region. Disabling the multiple discharging will restrict excessive heating of the ignition device as well as excessive wear of the plug electrodes. Alternatively, the number of multiple discharges may be reduced as engine rotational speed increases.
In case the relatively lean air-fuel mixture is switched to a richer air-fuel mixture (e.g., stoichiometric air fuel ratio mixture) when the engine operation region changes from a low engine load region to a high engine load region, the combustion chamber is filled with relatively rich non-stratified air-fuel mixture uniformly. In this high engine load region, the variation in the arrival time of the air-fuel mixture at the spark generating area does not affect ignition performance so much. Therefore, multiple discharging also may be limited to only a low engine load region.
The multiple discharging also may be limited to a fixed angular rotation interval of an engine crankshaft. This will in effect also reduce the number of multiple discharges in response to an increase in engine rotational speed, because the time period required for the engine crankshaft rotate through the fixed angular interval reduces as engine rotational speed increases.
The switching device should be turned on while the ignition coil still has stored energy, after it has been turned off first at an ignition timing, so that the ignition coil can store sufficient energy for the subsequent discharging by only a short turning on of the switching device.


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