US3597651A

US3597651A - Circuit to prevent engine reversal in a capacitor discharge ignition system

Info

Publication number: US3597651A
Application number: US852312A
Authority: US
Inventors: Arthur G Hufton
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1969-08-22
Filing date: 1969-08-22
Publication date: 1971-08-03
Anticipated expiration: 1988-08-03
Also published as: JPS4917977B1

Abstract

A resistive element is connected across a variable reluctance pickup used for generating a potential to initially charge and subsequently discharge the capacitor of an ignition system, thereby shunting a portion of the generated potential to ground. With the ignition system being energized but not operating, a transistor conducts to apply a bias potential to the pickup, to modulate the partially shunted generated pulses. A level detector is triggered when the generated pulses reach a given level to initially operate a blocking oscillator for charging the ignition capacitor and to subsequently discharge the same. If the engine kicks back on starting, the shunt circuit prevents operation of the level detector.

Description

United States Patent [72] Inventor Arthur G. Hulton Elk Grove Village, Ill. [21] ApphNo 852,312 [22] Filed Aug. 22,1969 [45] Patented Aug. 3, I971 [73] Assignee Motorola, Inc.

Franklin Park, Ill.

[54] CIRCUIT TO PREVENT ENGINE REVERSAL IN A CAPACITOR DISCHARGE IGNITION SYSTEM 7 Claims, 4 Drawing Figs.

[52] US. Cl 315/209, 315/218 [51 Int. Cl IIOSb 37/02 [50] Field 0! Search 123/41, 149; 315/209, 211, 212,213, 218

[56] References Cited UNITED STATES PATENTS 3,356,896 12/1967 Shano 315/211 X 3,515,109 6/1970 Farr Primary ExaminerRoy Lake Assistant Examiner Lawrence .1v Dah1 Attorney-Mueller and Aichele reach a given level to initially operate a blocking oscillator for charging the ignition capacitor and to subsequently discharge the same. If the engine kicks back on starting, the shunt circuit prevents operation of the level detector.

i1 la l PATENTED AUG 3 l9?! Inventor ART HUR G. HUFTON ATTYS CIRCUIT TO PREVENT ENGINE REVERSAL IN A CAPACITOR DISCHARGE IGNITION SYSTEM BACKGROUND OF THE INVENTION It is generally known, that when starting an outboard motor SUMMARY OF THE INVENTION lt is an object of this invention to provide a unique circuit for electrically preventing the reverse running of an internal combustion engine.

It is another object of this invention to provide an electrical circuit for preventing reverse operation of an internal combustion engine utilizing a capacitor discharge ignition system that is relatively inexpensive and more reliable than existing mechanical devices.

In one embodiment of this invention, a shaped rotor is driven in synchronism with the engine past a, variable reluctance pickup or sensor positioned in a spaced relation to the rotor. Because of the unique shape of the rotor, the pickup develops an output potential which reaches a given level in a timed relation to the engine r.p.m. A blocking oscillator is used to charge the ignition capacitor. When the generated pulses reach the given level, a level detector is operated to energize the blocking oscillator to charge the ignition capacitor. Subsequently, the generated pulses operate the level detector to discharge the ignition capacitor to tire the engine. A resistor is connected across the variable reluctance pickupto ground reference potential and shunts a portion of the generated potential. In addition, a transistor is connected between the output transistor of the blocking oscillator and the variable reluctance pickup and modulates the partially shunted pulses. When the ignition system is initially energized, the transistor conducts to couple a potential to the variable reluctance pickup means. When the engine is cranked, in the proper direction, the modulated, partially shunted pulses will reach the given level at approximately 150 r.p.m. to trigger the level detector, which energizes the blocking oscillator and charges the ignition capacitor. When the output transistor of the blocking oscillator is energized-,it' couples a potential to the transistor turning the same off. However, should the engine kickback on starting, the generated pulses will be sufficiently shunted by the resistor that even though they are modulated by the bias transistor the combination will not reach the given level thereby preventing operation of the engine. 1

DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION The ignition system of FIG. I includes a trigger circuit comprising a silicon controlled rectifier (SCR) 10, which connects the ignition discharge capacitor 12 to the primary winding 14 of the ignition coil 16. The secondary winding 18 of the ignition coil is connected to the distributor of the engine. A second silicon controlled rectifier or level detector 20 completes the trigger circuit and when. energized connects the primary winding 22 of transformer 24 to ground reference potential. The secondary winding 26 of the transformer 24 is connected across the gate 28 of the SCR 10.

A flywheel or rotor 30 rotates in the direction shown in FIG. 3 and carries on it a shaped element 32, whichis integral with the rotor. A variable reluctance pickup unit 34 is disposed on plate 35 adjacent to the path of the shaped element 32. The pickup 34 includes a winding 36 (FIG. 1 that surrounds a pole piece therein. As the flywheel 30 rotates, the element 32 passes the pickup 34 causing a change of flux in the winding 36. The shape of the rotor 30 is such that the air gap between the element 32 and the pole piece of the pickup closes as the flywheel rotates past the same. This causes a change in the magnetic reluctance thereby developing a potential across the winding 36 which will rise to a given level. The time required for the potential to reach this level varies with engine rpm. The SCR 20 will not conduct until the potential on the gate thereof reaches a predetermined level (about 0.06 of a volt). Therefore, the engine capacitor is in effect discharged sooner or later so that the ignition timing varies at a rate depending on engine r.p.m.

A blocking oscillator is used to charge the ignition capacitor 12 after it has been discharged. The blocking oscillator includes an NPN-type power transistor 38 that is connected to the battery 40 by diode 42 and ignition switch 44'. A filter circuit 46 removes any ripple from the power supply. The output electrode or emitter 48 of the transistor 38 is series connected to primary. winding 50 of transformer 52. A positive feedback path for the oscillator includesfeedback winding 54, which is coupled through the parallel combination of diode S6 and resistor 58 to the base or control electrode 60 of the transistor 38. The zener diode 62 is connected between the collector and emitter of transistor 38 to limit the voltage between these two electrodes for protective purposes.

An enabling'or semiconductor switching circuit 65 is provided for initiating operation of the oscillator to recharge the ignition capacitor 12 after each discharge of the capacitor by the triggering circuit.

In operation, the closing of ignition switch 44 couples a potential through resistor 69 to charge the capacitor 67 at a rate determined by resistor 68. Movement of the flywheel 30 past the pickup 34 at a predetermined r.p.m. induces a potential in winding 36 that reaches a level to trigger the SCR 20. This dischargesthe capacitor 67 therethrough and induces a potential in winding 26 of the transformer 24, which triggers the SCR 10 into conduction. When the SCR l0 conducts, it grounds the base electrode 70 of enabling transistor 72 through the diode 7,4 and primary winding 14 of the ignition coil 16. A current is then connected from battery 40 through resistor 75 to the base of transistor 38 causing that transistor to conduct. When the transistor 38 reaches saturation due to the action of feedback winding 54, a current is no longer induced in winding 54, therefore transistor 38 is rendered nonconducting. This causes the field of the transformer 52 to collapse inducing a current in winding of transformer 52 which is coupled by resistor 82., to charge the capacitor 12. Subsequently, the next time the trigger circuit is operated by the pickup 36, the capacitor will discharge through SCR 10 e and the primary winding 14 to produce a firing pulse in the secondary winding 18 of the ignition transformer. The diode prevents ringing in the circuit when the capacitor 12 discharges. And diode 87 across the primary winding 14 of the ignition transformer is used to surpress negative transients induced in the transformer by the collapsing of the field thereof.

FIG. 4shows the expected output waveforms from the sensor 34 adjacent to the rotor 30, A positive-going signal is required from the sensor 34 to trigger the level detector 20 to initiate operation of the system. As shown in FIG. 3, with the rotor 30 rotating in a clockwise direction, a strong positive pulse 90 is producedv followed by a small negative pulse 92. However, as indicated in. FIG. 2, should the rotor 30 be rotated in the opposite direction, i.e., counterclockwise, as a result of engine kickback, for instance, a'small positive pulse 94 is produced followed by a sharp negative pulse 96. The small positiveegoing signal generated by the rotor 30 going in the counterclockwise direction will not be sufficient to gate on the SCR until the engine rotates at approximately 200 r.p.m. However, it is not uncommon when engine kickback occurs to obtain rotor speed equivalent to 1,000 engine r.p.m. The generated positive pulse 94 at this r.p.m. is sufficient to gate on the SCR 20, and the ignition system will function as if the rotor were going in the proper direction. In order to prevent this reverse running of the engine a unique circuit has been developed.

Referring to FIG. 1, a resistor 98 is connected across the winding 36 of the sensor 34. This resistor will shunt a portion of the pulse developed across the winding 36 to ground. Therefore, should the rotor rotate in the reverse direction, even up to l,000 r.p.m., the generated pulse will be suffciently attenuated so the SCR 20 will not fire. However, it is desirable to be able to start the engine at a relatively low r.p.m. with the rotor 30 moving in the proper direction, .In order to accomplish this, a bias circuit is added which includes the transistor 100. The emitter 102 of transistor 100 is connected through the ignition switch 44 to the battery 40. The collector 104 thereof is connected in series with the winding 36 of the sensing element. The base 106 is connected through a divider network 108, which provides bias to the base, to the emitter 48 of the power output transistor 38 of the blocking oscillator. When the ignition switch is initially closed, the transistor 100 will be biased in a forward direction so a potential is coupled to the pickup 36 and the shunt resistor 98 to modulate the partially shunted input signals. The bias applied to the pickup 36 is selected so the pulse generated by the rotor 30 moving in the clockwise direction will gate on the SCR 20 at approximately l50 r.p.m. When the power output transistor 38 of the blocking oscillator is energized subsequent to the triggering of the SCR 20, a current will be connected from the emitter thereof to the base 106 of the transistor 100. This turns the transistor off removing the bias potential from the pickup 36. The capacitor 110 charges with the conduction of transistor 38 to keep the transistor 100 in the off condition with the engine running during the time the power output transistor 38 of the blocking oscillator is not conducting.

What has been described, therefore, is a unique circuit which prevents operation of a capacitor discharge ignition system with the engine operating in reverse but will provide for the starting ofthe engine at a predetermined low r.p.m.

lclaim:

1. In a capacitor discharge ignition system for an internal combustion engine having generator means driven in synchronism with the engine in a forward direction for producing electrical pulses, and trigger circuit means responsive to the pulses reaching a given level to discharge the ignition capacitor to produce an ignition pulse for the engine, the generated pulses reaching the given level in a timed relation to the engine r.p.m., the combination including, means for preventing the engine from operating in a reverse direction comprising, first circuit means connected between the pulse generating means and the trigger circuit means for reducing the pulse amplitudes by shunting a portion of the pulses from the generating means, and bias circuit means connected in circuit with the trigger circuit means and said first circuit means for selectively applying a bias thereto, said first circuit means shunting a portion of the generated pulses with the pulse generator means being driven in a reverse direction to prevent said pulses from reaching said given level thereby preventing reverse operation of the internal combustion engine, and with the generator means being driven in the forward direction, said bias circuit means amplitude modulating the pulses from the pulse generator means, said modulated pulses reaching the given level to operate the trigger circuit means at a preselected engine r.p.m. to produce an ignition pulse for the engine on starting.

2. The capacitor discharge ignition system of claim 1 wherein said first circuit means includes a resistance element connected across said generator means.

3. The capacitor discharge ignition system of claims 1 or 2 wherein said bias circuit means includes a transistor connected to the trigger circuit means for applying a bias to the same with the ignition system being energized and the engine not operating, said transistor being rendered inoperative with the operation of said trigger circuit means thereby removing the bias from the same during engine operation.

4. A capacitor discharge ignition system for an internal combustion engine, including in combination, rotating means driven in synchronism with the engine, variable reluctance pickup means positioned in a spaced relation to said rotating means and being responsive to the same for developing an output potential which reaches a given level in a timed relation to the engine r.p.m., first circuit means for charging the ignition capacitor, level detector means coupled to said first circuit means and the ignition capacitor for discharging the same, said level detector means being responsive to the generated potential reaching said given level to energize said first circuit means to initially charge the ignition capacitor, said level detector means being further responsive to the generated potential reaching said given level to discharge the ignition capacitor to fire the engine, second circuit means connected between said variable reluctance pickup means and said level detector means for shunting a portion of the output potential therefrom, and bias circuit means connected in circuit with said level detector means and said second circuit means for modulating the generated pulses, the electrical characteristics of said second circuit means and the electrical characteristics of said bias circuit means combining to form a characteristic impedance requiring a specific minimum potential generated in said pickup means to operate said level detector means to charge the ignition capacitor, thereby establishing a minimum r.p.m.

5. The capacitor discharge ignition system of claim 4 wherein said rotating means being driven on the order of r.p.m. in a predetermined direction in synchronism with the engine develops an output potential which combined with said bias potential operates said level detector to initially charge and subsequently discharge the ignition capacitor to fire the engine, and said rotating means being driven in the direction opposite said predetermined direction by engine kickback developing an output potential which is shunted by said second circuit means so that the same being amplitude modulated by said bias potential does not reach said given level to operate said level detector thereby preventing reverse running ofthe engine.

6. The capacitor discharge ignition system of claim 4 wherein said second circuit means includes a resistive element connected across said variable reluctance pickup means.

7. The capacitor discharge ignition system of claim 6 wherein said circuit means for charging the ignition capacitor includes a blocking oscillator having an output transistor, and wherein said bias circuit means includes a transistor having control and output electrodes, said output electrode thereof being series connected to said resistive element, and said control electrode being connected to said output transistor of said blocking oscillator, said transistor of said bias circuit conducting with said output transistor of said blocking oscillator inoperative to apply a bias potential to modulate the generated pulses, so that with the rot "ting means being driven on the order of 150 r.p.m. the pulses reach the given level to energize the first circuit means thereby energizing said output transistor of said blocking oscillator to initially charge the ignition capacitor, and said transistor of said bias circuit being rendered nonconductive with the operation of said output transistor of said blocking oscillator thereby removing the bias from said level detector so said generated pulses reach the given level only in timed relation to engine r.p.m. to provide ignition timing.

Claims

5. The capacitor discharge ignition system of claim 4 wherein said rotating means being driven on the order of 150 r.p.m. in a predetermined direction in synchronism with the engine develops an output potential which combined with said bias potential operates said level detector to initially charge and subsequently discharge the ignition capacitor to fire the engine, and said rotating means being driven in the direction opposite said predetermined direction by engine kickback developing an output potential which is shunted by said second circuit means so that the same being amplitude modulated by said bias potential does not reAch said given level to operate said level detector thereby preventing reverse running of the engine.

7. The capacitor discharge ignition system of claim 6 wherein said circuit means for charging the ignition capacitor includes a blocking oscillator having an output transistor, and wherein said bias circuit means includes a transistor having control and output electrodes, said output electrode thereof being series connected to said resistive element, and said control electrode being connected to said output transistor of said blocking oscillator, said transistor of said bias circuit conducting with said output transistor of said blocking oscillator inoperative to apply a bias potential to modulate the generated pulses, so that with the rotating means being driven on the order of 150 r.p.m. the pulses reach the given level to energize the first circuit means thereby energizing said output transistor of said blocking oscillator to initially charge the ignition capacitor, and said transistor of said bias circuit being rendered nonconductive with the operation of said output transistor of said blocking oscillator thereby removing the bias from said level detector so said generated pulses reach the given level only in timed relation to engine r.p.m. to provide ignition timing.