Internal-combustion engines – High tension ignition system – Having dwell control
Reexamination Certificate
2000-06-26
2003-03-04
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
High tension ignition system
Having dwell control
C123S618000, C123S652000
Reexamination Certificate
active
06526953
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ignition unit for an internal combustion engine for applying high voltage for ignition onto a spark plug and causing the spark plug to perform a spark discharge.
It is known that an amount of spark energy required for obtaining a normal combustion of mixed gas within an internal combustion engine is dependent on operating conditions of the internal combustion engine. The spark energy can be expressed by an amount of discharge current (secondary current) that is made to flow through spark discharge and by duration of spark discharge.
When the engine is in a low-revolution and low-load condition at the time of idling driving or the like, combustion of mixed gas is progressed in at a very sluggish speed due to a small loading amount of mixed gas to a combustion chamber and a slow flow velocity of turbulent flow (swirl flow or tumble flow) of mixed gas. For achieving stable combustion in such a low-revolution and low-load condition, it is thus necessary to increase the spark energy for supporting growth of a flame core to thereby support combustion of mixed gas. On the other hand, in a high-revolution and high-load condition, combustion is progressed at a high speed owing to a large loading amount of mixed gas to the combustion chamber and a high density of mixed gas so that a relatively small spark energy suffices.
A conventional ignition unit for an internal combustion engine was therefore arranged to be capable of supplying maximum spark energy required for various operating conditions of the internal combustion engine so as to prevent shortage of spark energy.
However, the supply of spark energy will be excess when the conventional internal combustion engine may be operated with smaller spark energy than the maximum required spark energy. This excess supply of spark energy will neither contribute to ignition of the mixed gas nor will it cause an excess increase in electrode temperature of the spark plug to thereby lead to faster exhaustion of the electrodes.
It is another drawback that the flow velocity of turbulent flow of the mixed gas becomes stronger (faster) the more the internal combustion engine approaches its high-rotation and high-load operating condition to cause repeated phenomena (so-called multiple discharge) wherein sparks are flown to a downstream side in the latter half of spark discharge in which the spark energy is decreasing until the spark discharge is finally blown off and repeatedly generated. In the presence of such phenomena, fusing or spattering of electrode materials of the spark plug is promoted owing to aggregation of sparks on the downstream side and owing to abrupt increases in electrode temperature to cause so-called irregular exhaustion with downstream side electrodes being particularly exhausted and the life of the spark plug is shortened in vain.
On the other hand, a so-called full-transistor type ignition unit is becoming common in these years for use as an ignition unit for an internal combustion unit that employs a switching element comprised of a semiconductor element such as a power transistor or the like as a means for switching between an energized/deenergized (interrupted) condition of a primary winding of the ignition coil for applying high voltage for ignition on the spark plug. In such an ignition unit of full-transistor type, time for energizing the primary coil of the ignition coil can be easily controlled by adjusting a time for driving the switching element (ON time). It is therefore possible in such a type of ignition unit for an internal combustion engine to control the spark energy to be of an amount required for combustion of mixed gas by controlling the time for energizing the primary wiring of the ignition coil in accordance with operating conditions of the internal combustion engine.
However, in performing control of the time for energizing the primary winding through the ignition coil before generation of spark discharge through the spark plug, an amount of energy stored in the ignition coil through the energizing will become small when the time for energizing is short, and the high voltage for ignition generated in a second wiring by interrupting energizing will accordingly become small. Consequently, when the time for energizing the primary wiring is set to be short for the purpose of, for instance, reducing the amount of spark energy at the time the internal combustion engine is in a high-rotation and high-load condition, the high voltage for ignition generated in the second wiring by energizing/deenergizing the first wiring of the ignition coil will become small so that it is impossible to obtain a high voltage for ignition suitable for a high-rotation and high-load operating condition wherein voltage required for ignition of the spark plug is high and may lead to misfire.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ignition unit for an internal combustion engine wherein spark energy is minimized without controlling time of energizing a primary wiring of an ignition coil prior to generation of spark discharge, and to achieve long-life of a spark plug by restricting multiple discharge that is apt to be generated under a high-rotation and high-load operating condition.
According to one aspect of the present invention, the ignition unit for an internal combustion engine comprises an ignition coil including a primary wiring connected to a power source unit and a second wiring forming a closed loop together with a spark plug equipped in the internal combustion engine; a spark discharge generating means for energizing current from the power source unit to the primary wiring of the ignition coil synchronously with the rotation of the internal combustion engine and for generating high voltage for ignition in the second wiring by interrupting the energizing current to thereby make the spark plug perform spark discharge; a primary wiring short-circuiting means for short-circuiting both ends of the primary wiring of the ignition coil in correspondence to instructions from an instruction means; a spark discharge duration calculating means for calculating a spark discharge duration required for combusting mixed gas through spark discharge of the spark plug based on an operating condition of the internal combustion engine; and a spark discharge interrupting means for forcibly interrupting spark discharge of the spark plug by short-circuiting both ends of the primary wiring of the ignition coil by actuating the primary wiring short-circuiting means in accordance with the spark discharge duration calculated by the spark discharge duration calculating means.
By short-circuiting both ends of the primary wiring through the primary wiring short-circuiting means when spark discharge is being generated, current starts to flow through a closed loop formed by the primary wiring and the primary wiring short-circuiting means through a magnetic flux remaining in the ignition coil. This current being gradually increased and voltage which is of opposite polarity to that of the high voltage for ignition that had been generated in the secondary wiring when spark was generated, being induced on the secondary wiring, through magnetic flux remaining in the iron core of the ignition coil, spark discharge at the spark plug is forcibly interrupted or extinguished.
Spark discharge will not be immediately interrupted upon short-circuiting both ends of the primary wiring, but the spark discharge is only interrupted when a primary current has increased to a level for inverting the polarity of induced voltage generated in the secondary wiring after short-circuiting both ends of the primary wiring. It is therefore necessary to perform short-circuiting of both ends of the primary wiring through the switching element prior to an interrupting timing for the spark discharge, wherein the time between short-circuiting both ends of the primary wiring and interrupting the spark discharge becomes longer the more magnetic flux is remaining in the ignition coil and short
Argenbright Tony M.
Hoang Johnny H.
NGK Spark Plug Co. Ltd.
Sughrue & Mion, PLLC
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