US2433650A - Ignition system - Google Patents

Description

Dec. 30, 1947. 5 ET AL I IGNITION SYSTEM Filed Sept. 25, 1946 fledh w 1| ew It T rl .m

c IE/ e e o h w awn T o .n v/ v 1 T b Patented Dec. 30, 1947 UNITED IGNITION SYSTEM Reginald T. Coe, Rugby, Thomas F. Robinson,.

Kenilworth, and Douglas F. Welch, Rugby, England, assignors to General Electric Company, a corporation of New York Application September 25, 1946, Serial No. 699,264 In Great Britain February 8, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires February 8, 1964 Claims.

This invention relates to electric ignition systems and more particularly to ignition systems for internal combustion engines in which the main low voltage magneto winding is connected to supply its generated voltage to the primary winding of a step-up transformer, the secondary windin of which is connected to the spark plug or plugs. In these systems the contact breaker is connected in parallel with the magneto and.

primary transformer windings and distribution is efiected either before or after the transformer or transformers. If distribution is effected before the transformer then a separate transformer is used with each spark plug and is preferably placed at or near the plug whereas if distribution is effected after the transformer, a single transformer only is necessary, and its high voltage output is passed through the distributor.

An object of the present invention is to provide an improved ignition system. A further object of the present invention is to improve electrical ignition systems of the separate transformer type, so as to provide a system which is particularly suitable for high altitude and high spark frequency on account of the reduction of duration of after current in the discharge through the distributor, this after current being the decaying direct current component of current which follows the main oscillatory discharge.

Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

The invention is particularly adapted to ignition systems employing low tension distribution, where it is desirable to damp down and eliminate the current flowing in the primary circuit of the transformer before the brush or other contact device of the distributor transfers the primary circuit connection to the segment feeding the next sparking plug.

It is known that the after current duration can be decreased by the use of the resistance connected in series with the primary winding of the transformer between it and the contact breaker, but where an appreciable reduction in after current is required this method has the drawback of also leading to an appreciable reduction in the open circuit magneto output voltage. The present invention offers an improvement over this known arrangement.

The invention consists in inserting in the connection between the transformer primary and the 2 contact breaker a suitable series condenser hav ing a parallel connected damping resistance. Where low tension distribution is employed, it will usually be preferable to have one series condenser with damping resistance connected between the contact breaker and distributor in preference to inserting one in each lead between the distributor and step-up transformers.

The series capacity should have such a Value as to offer an appreciable impedance to the after current at spark repetition frequency, but yet to offer only a relatively low impedance to the low frequency oscillatory component of the transformer primary current, the frequency concerned in the latter case being appreciably above that of the spark repetition frequency.

For a given value of series capacity the damping resistance should be of such a value as to clamp down the current in the primary of the transformer in the required fraction of the interspark period. A preferable value of damping resistance is in the region of that required to critically damp the oscillation associated with the series capacity in conjunction with the effective inductance of the magneto winding and the transformer primary winding in series; that is, the damping resistance should be about ohms, where Lia and Llb are the inductances of the magneto winding and the transformer primary winding in henrys and Cs is the series capacity in f arads.

The invention will be better understood by reference to the accompanying drawing in which Fig. 1 shows the invention as applied to an ignition system of the separate transformer type with hightension distribution. Fig. 2 shows the invention as applied to an ignition system with low tension distribution and Fig. 3 is a diagram of the wave form of the primary current in a separate transformer system,

Referring to Fig. 1 of the drawing, there is shown an ignition system comprisin a suitable power supply such as a magneto having an output winding I connected to energize a primary winding 2 of a step-up transformer 3, The transformer has a secondary winding 4 arranged to be sequentially connected through a conventional distributor 5 to a plurality of spark plugs 6. The magneto winding l is periodically shorted by a conventional contact breaker 1 having contacts 8 connected in parallel with the winding I. Contacts 8 are shorted by a conventional condenser 9. In accordance with the present invention, after current damping is accomplished by the provision of a condenser l connected in series relation in the circuit interconnecting windings I and 2, the condenser l0 having connected in parallel therewith a damping resistance II. The capacity to earth of each secondary lead from the transformer to the plug including effective capacity associated with the transformer winding, distributor, and plug is represented schematically by plates l2.

Fig. 2 shows an embodiment of the invention in an ignition system with low tension distribution where the series condenser [0 with parallel resistance II is connected between the contact breaker l and the low tension distributor while l3 and I4 represent typical step-up transformers in the separate leads to the spark plugs 6.

Fig. 3 shows the effect of the invention on the primary current of the transformer. The waveform of primary current for the normal separate transformer system is shown in (a) and (b) shows a typical wave-form with the present invention where the current is rapidly damped to a negligible value without affecting appreciably the initial oscillation of current Which is instrumental in producing the secondary spark voltage. The positions of contact opening are shown at O and contact closing occurs at some intermediate point C.

The invention may be used in conjunction with any type of transformer including both high andlow coupling coefiicient types, but a preferable arrangement is to use it with thecircuit described in British Patent No. 545,857 in which the constants of the circuit, including the coupling coefll'cient of the transformer, are chosen to" give a special peaky wave-form of. secondary open. circuit voltage which results in a. short after-current duration. The inclusion with this circuit of the series condenser and damping. resistance of the present invention will not greatly change the wave-form of the first half cycle of open circuit secondary voltage so that the relatively short after current duration is further decreased by the incorporation of the present" invention, and good performance with shunt resistance across the external plug gaps, as is also associated with the wave-form, is also obtained with the present invention. Auto-transformer connection may be used if desired without affecting the principle of operation.

While we have illustrated.- and described particular embodiments of our invention, modifications will occur to those skilled in the art. We desire it to be understood, therefore, that our invention is not to be limited tothe particular arrangements described, and we intend in the appended claims to cover all modifications which do not depart from. the spirit and scope ofour invention.

What we. claim as new and desire-tosecure" by Letters Patent of the United Statesis:

1. In an, ignition: system the combination comprising a magneto having. an output winding, a step-up transformer having primary and second.- ary windings, said; primary winding of the: stepup transformer being connected to be: energized from said magneto output winding, a spark plug connected to be energized from said secondary winding ofthe step-up transformer, a distributor arranged to cause energization of said spark plug at timed intervals, and means for reducing the flow of after current during the interspark period, said last-mentioned means comprising a series condenser in the circuit interconnecting said magneto output winding and said primary Winding and a damping resistance connected in parallel with said series condenser.

2. An ignition system comprising in combination a power supply comprising an output winding', a transformer having primary and secondary windings, a spark plug connected to be energized from said secondary winding, means constituting an electric circuit interconnecting said primary winding, a periodically operated contact breaker connected in parallel with said output winding to cause periodic oscillatory discharges across said spark plug and means for reducing the after current duringthe interspark period comprising a condenser connected in series relation in said circuit and a damping resistance connected in parallel with said condenser.

3'. An, ignition system comprising in combination a plurality of spark plugs, a step-up transformer having a primary winding. and a secondary winding, means including a distributor for sequentially connecting said spark plugs to said secondary winding, 9. magneto having an output winding connected through a circuit to energize said primary winding, a contact breaker and a first condenser connected in parallel across said output winding, a second condenser connected in series relation in said circuit and a damping resistance connected across said second condenser.

4. An ignition system comprising in combination, a magneto having an output winding, a step-up transformer having primary and secondary windings, a spark plug connected to be energized from said secondary winding, circuitmeans including a distributor for connecting said primary winding to said magneto output winding to be energized thereby; a contact breaker connected in parallel with said magneto output winding, a series condenser connected between said contact breaker and said: distributor and a damping resistance connected in parallel with said condenser. V

5. In an ignition system a plurality of spark plugs, a transformer having primary and secondary windings associated with; each spark plug, the secondary winding of each transformer being connected toenergize its associated spark plug; a power supply having an output winding, an electric circuit including a distributor for sequentially connecting said output-winding to the primary windings of the transformers associated with said spark plugs, aperiodically operated contact breaker connected in parallel with said output winding, and current damping means comprising a condenser connected in series relation in said circuit and a resistance connectedin parallel with-said condenser. v

REGINALD I THOMAS E RoerNsfoN} DOUGLAS F. WELCH.-

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