Internal-combustion engines – High tension ignition system – High frequency ignition system
Utility Patent
1998-11-30
2001-01-02
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
High tension ignition system
High frequency ignition system
C123S605000
Utility Patent
active
06167875
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to ignition systems for internal combustion engines, and particularly, to a multiple spark capacitive discharge ignition system for such an engine.
In internal combustion engines, it is known that the physical nature of the fuel or fuel/air charge injected into the cylinder varies depending upon engine operating conditions. Specifically, at low engine speeds, the fuel charge is injected into the cylinder in the form of a stratified cloud of fuel particles. The cloud of fuel particles is termed stratified because the density of the fuel particles within the cloud is not constant, i.e., not homogeneous throughout the charge. At higher engine speeds, the fuel charge is injected into the cylinder in what is termed to be a “homogeneous” cloud of fuel particles. The charge is termed homogeneous because the density of fuel particles in the fuel charge is relatively constant throughout the charge.
A single ignition spark or a small number of ignition sparks anywhere within a homogeneous fuel charge will cause complete combustion of the fuel charge. This is not so for a stratified fuel charge. With a stratified injection of fuel, it has been found desirable to provide a greater number of ignition sparks (than is provided under homogeneous conditions) in order to ensure that the stratified fuel charge is adequately or completely ignited. U.S. Pat. Nos. 5,170,760 and 4,653,459 generally illustrate ignition systems for providing a plurality of ignition sparks to ignite a stratified or non-homogeneous fuel charge in the cylinder.
SUMMARY OF THE INVENTION
The invention provides an ignition system for an internal combustion engine having one or more cylinders. The ignition system generates more ignition sparks per ignition event when the engine is operated in the stratified fuel injected mode than when the engine is operated in the homogeneous fuel injection mode. Generally speaking, the system includes an electronic control unit (“ECU”) for generating ignition signals for the respective cylinders, an input/logic multiplexer for multiplexing the ECU control signals, a direct current to direct current (“DC—DC”) converter for charging an ignition capacitor, a silicon controlled rectifier (“SCR”) for discharging the ignition capacitor, an ignition trigger circuit for triggering the SCR and an ignition distribution network for distributing the energy discharged from the ignition capacitor to the appropriate ignition coil.
The DC—DC converter includes a pulse width modulator which generates, in response to the inputs from the ECU, a high frequency output of at least 1000 hertz frequency. Preferably, however, the frequency of the pulse width modulator output is 3.0 khz. The pulse width modulator drives a series of parallel connected high power insulated gate bipolar transistors (“IGBTs”) connected through a transformer to a power supply. The power supply voltage is generated by the alternator. Energizing of the transistors by the pulse width modulator at a rate of approximately 3.0 khz causes a flyback voltage to be generated at the primary of the transformer. The flyback voltage is, through mutual inductance, transferred to the secondary of the transformer and “stepped-up” to approximately 200 to 300 volts. This voltage charges an ignition capacitor to approximately 200 to 300 volts. The ignition capacitor is selectively discharged by triggering the SCR to provide electrical energy to the ignition coil which generates a spark to ignite the fuel charge.
The current flowing through the IGBTs is monitored using a current sensing resistor connected in series with the IGBTs. The voltage across the current sensing resistor is “fed back” to the pulse width modulator. The pulse width modulator varies the width of the output pulses generated by the pulse width modulator to compensate for variations in the voltage of the power supply. Thus, as the voltage supplied by the alternator increases, the pulse width of the output of the pulse width modulator decreases. This allows the ignition system to operate effectively from a low voltage of approximately eight volts (which occurs upon engine cranking) to a high voltage of approximately 30 volts (which occurs during high speed engine operation). The use of current sensing to indirectly sense the variations of the supply voltage eliminates the need to compensate the ignition system for variations in the temperature of the system.
It is an advantage of the invention to provide a capacitive discharge ignition system that, in general, energizes the engine spark plug or spark plugs at a higher energy level or for a longer duration when the engine is operating under stratified fuel injection conditions than when the engine is operating under homogeneous engine operating conditions.
It is another advantage of the invention to provide an ignition system that increases the number of strike opportunities per ignition event when the fuel charge is stratified relative to when the fuel charge is homogeneous.
It is another advantage of the invention to provide the ignition sparks at a rate which at least exceeds 1000 hertz.
It is another advantage of the invention to provide an ignition system for an internal combustion engine that utilizes as its voltage source the voltage from the alternator.
It is another advantage of the invention to provide an ignition system for an internal combustion engine that utilizes a transformer which can accommodate larger voltage ranges.
It is another advantage of the invention to provide an ignition system for an internal combustion engine that charges the ignition capacitor using a flyback voltage.
It is another advantage of the invention to provide an ignition system which senses the current flowing through the transformer to eliminate the need for temperature compensation of the ignition system and improve the efficiency of the ignition system.
Other features and advantages of the invention are set forth in the following detailed description and claims.
REFERENCES:
patent: 5183024 (1993-02-01), Morita et al.
patent: 5429103 (1995-07-01), Rich
patent: 5471362 (1995-11-01), Gowan
French Michael J.
Skrzypchak Mark J.
Fletcher, Yoker & Van Someren
Gimie Mahmoud M
Kamen Noah P.
Outboard Marine Corporation
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