Turn-off protected ignition system for internal combustion engines
First Claim
1. Turn-off protected ignition system for internal combustion engine, havinga source of electrical supply (1);
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Accused Products
Abstract
A transistorized ignition system is protected against interruption of power supply by, for example, turn-off of the main or ignition switch while the transistor is in conductive condition so that, upon sudden interruption, an ignition event could be triggered at a time unsuitable for the remainder of the engine. A turn-off protection circuit is provided which includes a coupling resistor connected to the junction of the primary of the ignition coil and the main ignition current supply transistor thereto. The coupling resistor is connected in a circuit which holds the main current supply transistor in conductive condition, supplied from the energy stored in the ignition coil even after the main, ignition switch has been opened. A closed circuit for current flow due to this stored energy is provided within the overall ignition circuit. Preferably, the system includes a coupling transistor, connected across the power supply, which is blocked when the main transistor is conductive, so that the main transistor is controlled by power supply voltage appearing at the collector of the coupling transistor; the coupling resistor of the turn-off protected circuit then applies the inductive voltage from the coil to the collector terminal of the coupling transistor, and hence simulates continued power supply to the main current supply transistor to continue to hold it conductive and thus prevent abrupt turn-off and initiation of an undesired ignition event.
10 Citations
11 Claims
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1. Turn-off protected ignition system for internal combustion engine, having
a source of electrical supply (1);
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2. a main switch (2) connecting the source (1) to the ignition system, said system having
an ignition coil (8); -
a main ignition current supply transistor (9,
12) connected in series with said ignition coil (8) to control current flow therethrough;a pulse source (25) providing pulses to command ignition events; a control transistor (36) interconnecting the pulse source (25) and the main transistor (9,
12) to control conduction thereof in accordance with pulses applied to said control transistor (36);a coupling transistor (41) connected between said control transistor (36) and said main transistor (9,
12), said coupling transistor being connected to be in blocked condition when said main transistor (9,
12) is conductive,and comprising, in accordance with the invention, a turn-off protection circuit (49) including a stabilized voltage circuit including a coupling element (51) connected to said source, a Zener diode (18) connected to the coupling element (51), and a stabilized-voltage current coupling element (17) connected to the junction of said coupling element (51) and the Zener diode (18) and providing a stabilized source (B) of current when connected to said electrical supply source (1), said control transistor being supplied from said stabilized voltage circuit; a transistor coupling resistor (50) connected to the junction between the primary (7) of the ignition coil and the main transistor (9,
12) and further to the control electrode of the main transistor to supply operating voltage to the main transistor from energy stored in the coil (8) to hold the main transistor in conductive condition during decay of voltage in the coil upon interruption of said main switch if, at the moment of interruption, said main transistor was conductive;energy storage means (19) connected to the stabilized-voltage current coupling element (17) to supply energy to the stabilized voltage circuit in the absence of power supplied from said source of electrical supply (1) to hold the coupling transistor (41) in blocked condition and prevent bypassing of the energy from said coil through said coupling transistor; and means (6, 53,
54) establishing a closed circuit for current flow due to the stored energy in the coil (8) independent of said switch (2).
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Specification