Ignition Safety Circuit

Abstract

Disclosed herein is a safety circuit for an engine ignition system which includes a semiconductor switch which is in the form of two transistors and which is connectable to the engine alternator, the battery and the high-voltage power supply. The semiconductor switch is responsive to increases in current output from the alternator. When the engine starter rotates the alternator at speeds exceeding 50 revolutions per minute, the switch closes and provides a circuit path connecting the battery to the high-voltage power source to cause ignition voltages to start the engine.

Description

BACKGROUND OF THE INVENTION

Problems have been encountered in the use of electronic ignition circuits for engines. When the ignition switch is in an "on" position, the engine can be started without being turned over by the starting device. As for instance, when adjusting the engine, if the flywheel is accidentally moved slightly or the ignition timing is advanced, an ignition voltage can be produced in the spark plugs causing the engine to start.

SUMMARY OF THE INVENTION

The invention provides a safety circuit which is connectable to a device for generating voltage in response to engine speed, as for instance, an engine alternator, a battery or other source of electrical energy, such as a magneto, and an ignition device which can include a high-voltage power supply in the form of an ignition coil and connected spark plug. The safety circuit prevents production of ignition voltages by the high-voltage power supply if the engine speed is less than that produced by the engine-starting apparatus, such as for example, a starting motor or a handcrank or rope.

The circuit includes a semiconductor switch which is in the circuit path between the source of electrical energy or battery and the ignition device, and which is in the form of a driver transistor coupled to an output transistor. The output transistor becomes conducting in response to current produced by the voltage-generating device or alternator when the engine is cranked by the engine-starting device to complete the circuit path between the source of electrical energy or battery and the ignition device. The output current of the voltage-generating device or alternator is insufficient to make the output transistor conducting when the engine output shaft is rotating at less than, for instance, 50 revolutions per minute, thus requiring operation of the engine-starting device to provide ignition voltages.

It is an object of the invention to provide an ignition safety circuit which prevents the engine from starting when the ignition switch is in an "on" position and the flywheel is accidentally moved or the ignition timing is advanced.

It is another object of the invention to provide a safety circuit which connects a source of electrical energy, such as a battery to an ignition device and which is also connectable to a voltage-generating device responsive to engine speed, such as an engine alternator, and which is operable in response to an increase in engine speed to a minimum speed so as to complete the circuit path between the battery or other source of electrical energy and the ignition device.

It is an object of the invention to provide a safety circuit for an engine employing an electronic ignition system which prevents the engine from starting in the absence of the use of the engine starter motor or the engine-cranking device when the ignition switch is in an "on" position.

Further objects and advantages of the present invention will become apparent from the following description and accompanying drawings.

DESCRIPTION OF THE DRAWINGS

The FIG. is a schematic diagram of a safety circuit in accordance with the invention.

DETAILED DESCRIPTION

The FIG. shows a voltage-generating device or alternator 5, a battery or source of electrical energy 7 and an ignition device 9 which can include a high-voltage ignition coil connected to a spark plug. In accordance with the invention, means are provided for connecting the voltage-generating device 5, the source of electrical energy 7 and the ignition device 9 for providing current flow to the ignition device 9 in response to an output current of a predetermined magnitude from the voltage-generating device 5. In the disclosed embodiment the means is enclosed in a broken line rectangle designated generally 4 and includes first, second and third input terminals 6, 8 and 10 respectively.

The means also includes a semiconductor switch which comprises first and second transistors respectively, 12 and 14. Transistor 12 has a base 16, collector 18 and emitter 20. Transistor 14 has a base 22, collector 24 and emitter 26. The circuit also includes a double diode 28 with first and second anodes 30 and 32, and a cathode 34. Alternatively, two single diodes could be employed.

Also included in the means is a first resistor 36. One side of resistor 36 is connected to the cathode 34 by a lead 38. The other side of the resistor 36 is connected to the base 16 of the transistor 12 by a lead 40. The emitter 20 of the transistor 12 is connected to ground 41 by a lead 42. The circuit is provided with a capacitor 44 which has one side connected to the base 16 of the transistor 12 by a lead 46. The other side of capacitor 44 is connected to the emitter 20 by a lead 48.

The transistors 12 and 14 are coupled by a resistor 50 which has one side connected by a lead 52 to the collector 18 of transistor 12. The other side of resistor 50 is connected by a lead 54 to the base 22 of the transistor 14. The emitter 26 of transistor 14 is connected by a lead 53 to input terminal 10.

The FIG. also shows an ignition switch 56. The input terminal 10 is connected by a lead 55 to one terminal of ignition switch 56.

The connection between the transistor 14 and the ignition device 9 is provided by a lead 59 which connects the collector 24 of transistor 14 to an output terminal 57. The output terminal 57 is connected by a lead 64 to one terminal 60 of the ignition device 9. The other terminal 66 of the ignition device 9 is connected by a lead 68 to ground 41.

The other side of the ignition switch 56 is connected by a lead 78 to terminal 76 of the full-wave diode bridge 72 of the alternator or voltage-generating device 5. The bridge includes first, second, third and fourth diodes respectively 73, 75, 77 and 79 which are interconnected in the usual manner with the cathode of diode 73 connected to the anode of diode 75, the cathode of diode 75 connected to the cathode of diode 77, the cathode of diode 79 to the anode of diode 77, and the anode of diode 73 connected to the anode of diode 79. The switch 56 is also connected to one side of the battery or source of electrical energy 7 by a lead 82. The other terminal of battery 7 is connected to ground 41 by a lead 83.

To prevent thermal runaway of transistor 14 at high temperature the circuit can also include a third resistor 81 which has one terminal connected to the lead 53, and another terminal connected to the lead 54.

The connection between the terminal 84 of diode bridge 76 and the input terminal 6 is provided by a lead 86. The input terminal 6 is connected by a lead 87 to the anode 30 of diode 28. The terminal 88 of the bridge 72 is connected by a lead 90 to the input terminal 8. The bridge 72 is also grounded by a lead 92.

In operation of the circuit of the invention, when the ignition switch 56 is closed, a circuit path from the battery 7 to the input terminal 60 of the ignition device 9 is open, because the transistor 14 is normally in a nonconducting state. Thus, transient pulses or currents produced by the alternator 5 which could be caused by manually moving the engine flywheel will not cause the engine to start. When the engine is turned over by the starter motor or the handcrank and the alternator output reaches a certain voltage value, the AC signal provided through leads 86 and 90 and the pulse supplied by the diode 28 to transistor 12, will bias the transistor 12 in the forward direction making the transistor 12 conducting. This causes a current flow through resistor 50 to turn on or make conducting the transistor 14 and provide a low resistance current path from the emitter 26 to the collector 24, thus completing the circuit path from the battery 7 to the ignition device 9, thus providing ignition voltage for the spark plugs.

In one embodiment of the invention, the circuit components have the following values: the capacitor 44 has a value of 25 microfarads and 25 volts; the transistor 12 is an SPS 3374; the transistor 14 is an SP 2470; the resistor 36 has a value of one-half watt and a resistance of 390 ohms; the resistor 50 has a value of 2 watts and a resistance of 68 ohms; the diode 28 can be two G100B diodes or two 1 N4002 diodes, the resistor 81 is a one-half watt, 16-ohm resistor.

By varying the values of the circuit components, the transistors 12 and 14 can be made conducting to complete the circuit path from the battery 7 to the ignition device 9 only when the alternator 5 is rotating at speeds greater than 50 revolutions per minute. These rates of rotation are easily exceeded when the engine is cranked by a rope, by an electric starter or by other starting devices. Thus, the safety circuit does not affect normal engine operation.

Various of the feature of the present invention are set forth in the following claims.

Claims

I claim:

1. An engine including an electric generator device for directly generating voltage proportionately to engine speed, a source of electrical energy, an ignition device, and means connected to said voltage-generating device, said source of electrical energy and said ignition device and responsive to the magnitude of the voltage generated by said device for connecting said source of electrical energy to said ignition device to energize said ignition device in response to an output voltage from said voltage-generating device of a predetermined magnitude caused in response to the attainment of a minimum engine speed.

2. The combination of claim 1, wherein said means connected to said voltage-generating device, said source of electrical energy and said ignition device comprises first and second transistors, each of said transistors having a base, emitter, and collector, said collector of said first transistor being connected to said base of said second transistor, said emitter of said second transistor being connected to one terminal of said source of electrical energy, said collector of said second transistor being connected to said ignition device, said emitter of said first transistor being connected to the other terminal of said source of electrical energy, and said base of said first transistor being connected to said voltage-generating device.

3. In combination, an engine alternator, said alternator including a full-wave rectifier bridge having first, second, third and fourth diodes, each of said diodes having an anode and cathode, said cathode of said first diode being connected to said anode of said second diode, said cathode of said fourth diode being connected to said anode of said third diode, said cathode of said second diode being connected to said cathode of said third diode, said anode of said first diode being connected to said anode of said second diode, a battery, an ignition device having an input terminal, a switching device comprising first, second and third input terminals, an output terminal, a double diode having two anodes and a cathode, one of said anodes being connected to said first input terminal, the other of said anodes being connected to said second input terminal, first and second transistors with each of said transistors having a base, collector and emitter, a first resistor, a second resistor, one side of said first resistor being connected to said cathode of said double diode, the other side of said first resistor being connected to said base of said first transistor, said emitter of said first transistor being connected to ground, a capacitor, one side of said capacitor being connected to said base of said first transistor, the other side of said capacitor being connected to said emitter of said first transistor, one side of said second resistor being connected to said collector of said first transistor, the other side of said second resistor being connected to said base of said second transistor, said emitter of said second transistor being connected to said third input terminal, said collector of said second transistor being connected to said output terminal, said output terminal being connected to said input terminal of said ignition device, an ignition switch having first and second terminals, one of said terminals of said ignition switch being connected to said third input terminal, the other terminal of said ignition switch being connected to one terminal of said battery, the other terminal of said battery being connected to ground, said cathodes of said second and third diodes of said rectifier bridge being connected to said second terminal of said ignition switch, said cathode of said first diode and said anode of said second diode of said rectifier bridge being connected to said first input terminal, and said cathode of said fourth diode and said anode of said third diode of said rectifier bridge being connected to said second input terminal.

4. The device of claim 3, including a third resistor having one terminal connected to said emitter of said second transistor and another terminal connected to said base of said second transistor.

5. An engine ignition safety circuit comprising a battery adapted to power an ignition device, an engine alternator adapted to generate a voltage having a magnitude responsive to engine speed, and transistor switch means connected to said engine alternator, connected to said battery, and connected to the ignition device and responsive to the magnitude of the voltage generated by said alternator, said switch means being operable in response to output voltage of a predetermined magnitude from said alternator in response to the attainment of minimum engine speed to electrically connect the battery to the ignition device.