Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
2002-07-29
2003-06-03
Mohanty, Bibhu (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
C123S598000, C123S179500
Reexamination Certificate
active
06571769
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a capacitor discharge type internal combustion engine ignition device.
BACKGROUND OF THE INVENTION
A capacitor discharge type internal combustion engine ignition device is comprised of an ignition coil; an ignition capacitor provided at the primary side of the ignition coil and charged by an output voltage of a predetermined power supply at one polarity; a discharge thyristor, which becomes an on-state when an ignition signal is given and discharges a charge of the ignition capacitor through the primary coil of the ignition coil; a signal generating portion for generating a signal to obtain rotational information on the internal combustion engine; and an ignition control portion which gives the ignition signal to the discharge thyristor at an ignition position (a rotational angle position of a crank shaft at a time of performing an ignition operation) of the internal combustion engine decided based on the rotational information obtained from the signal generated by the signal generating portion.
As for the power supply to charge the ignition capacitor, an exciter coil is often used, which is provided inside a magneto-generator driven by the internal combustion engine and synchronizes with rotation of the engine so that an alternating voltage is induced.
In recent years, in order to purify an exhaust gas of the engine and attempt to reduce a fuel cost, it is necessary for the engine to have complex ignition characteristics. For this reason, there are frequent cases where a microcomputer is installed in the ignition control portion and the ignition position is decided in a software manner.
In the case where the ignition signal is generated at the ignition position decided in the software manner by using the microcomputer, a reference position is set at a position sufficiently advanced more than the rotational angle position corresponding to a top dead center of the internal combustion engine, and a time required for the engine to rotate to the ignition position arithmetically operated from the reference position is found as an ignition position detection time (time to be measured by the ignition timer for detecting the ignition position). When the reference position is detected, an ignition timer is allowed to start measuring the ignition position detection time and generate the ignition signal when the measurement has been completed.
As described above, in the internal combustion engine which controls the ignition position by using the microcomputer, since it is necessary to detect the reference position as the basis for measuring the ignition position decided in the software manner and the ignition position at a starting time and an extremely low speed state, the signal generating portion is comprised in such a manner that a reference position detection signal is generated at the reference position set at a position sufficiently advanced more than the rotational angle position of the crank shaft corresponding to the top dead center of the engine, and the ignition position detection signal for extremely low speed state is generated at the position adequate as the ignition position at the starting time and the extremely low speed state of the internal combustion engine.
Further, the ignition control portion is provided with an ignition control portion for extremely low speed state for giving the ignition signal to the discharge thyristor when the ignition position detection signal for extremely low speed state is generated and an ignition control portion for steady state for giving the ignition signal to the discharge thyristor at the ignition position decided based on the rotational information on the internal combustion engine, which is obtained from the output signal of the signal generating portion.
In the case where the ignition position is decided by using the microcomputer, if a battery is provided, the microcomputer can be operated from the starting time of the engine and, therefore, there arises no problem at all. However, in the case where no battery is provided or in the case where there is a necessity to make it possible to operate the engine even when the battery is exhausted for safety reason, it is necessary to give a power supply voltage to the microcomputer by an output of a generator mounted on the engine. For example, in an outboard motor, the engine is required to operate even when the battery is exhausted. For this reason, in the ignition device of this type, a control power supply circuit is provided, which rectifies a negative half-wave output of the exciter coil not used for charging the ignition capacitor and generates a constant direct current voltage so that, from this power supply circuit, the power supply voltage is given to the ignition control portion.
In a battery-less ignition device having a microcomputer provided with power voltage from the output of the control power supply circuit fed by the generator mounted on the internal combustion engine instead of a battery, since the microcomputer is not allowed to normally operate until the output voltage of the generator is raised to a certain level at a starting time of the engine, the ignition operation can not be performed as long as the rotational speed of the internal combustion engine is low. Further, even when the microcomputer can be normally operated, as long as the rotational speed of the engine is low, since fluctuation in the rotational speed accompanied by a stroke change of the engine is large, it is difficult to accurately measure the ignition position arithmetically operated by the microcomputer, thereby it is not possible to stably perform the ignition operation.
For this reason, in the battery-less ignition device, a signal is generated from the generator or a signal generator mounted on the engine at a position adequate as the ignition position at the starting time and the extremely low speed state of the engine, and when this signal has been generated, the ignition signal is given to the discharge thyristor through a hardware circuit, so that an ignition at the starting time and the extremely low speed state (a speed region below an idling rotational speed) is stably performed.
As described above, in the battery-less capacitor discharge type ignition device which decides the ignition position in the software manner by using the microcomputer, in order to stably perform the ignition at the starting time and the extremely low speed state of the engine, the ignition control portion for extremely low speed state is provided, wherein the ignition signal is given to the discharge thyristor through the hardware circuit. However, in a conventional ignition device of this type, since the power supply voltage was given to the ignition control portion for steady state provided with the microcomputer and to the ignition control portion for extremely low speed state from the same power supply circuit, there was a problem that the ignition control portion for extremely low speed state delays in starting an operation at the starting time of the engine.
That is, since the microcomputer constantly consumes electric power, when the rotational speed of the engine is low and a peak value of the negative half wave output voltage of the exciter coil is not in a sufficiently high level state (in a state whereby the peak value of the output voltage of the negative half-wave of the exciter coil barely reaches the power supply voltage of the microcomputer), even if the power supply circuit outputs the voltage of a value (5V) necessary for operating the microcomputer while the exciter coil generates the negative half-wave output voltage, the output of the control power supply circuit stops as soon as the exciter coils enters a time period for outputting a positive half-wave voltage. Accordingly, until the control power supply circuit, which drives the microcomputer, is put into a state of stably outputting a voltage held at a set value, it is necessary to wait until the rotational speed of the engine is further increased so that the output v
Kokusan Denki Co. Ltd.
Mohanty Bibhu
Pearne & Gordon LLP
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