US2772320A

US2772320A - James l

Info

Publication number: US2772320A
Authority: US
Publication date: 1956-11-27
Anticipated expiration: 1973-11-27

Description

1956 c. B. KNUDSON ETAL 2,772,320

ENGINE IGNITION SYSTEMS OR THE LIKE Filed Sept. 4, 1953 w. 5 F 2 L 0 /wo E JAMES L. BUIE h w A CLARENCE B. muosou INVENTORS S7AET EON W I) g By M FREQUENCY" 'QP T THEIR ATTORNEY United States Patent ENGINE IGNITION SYSTEMS OR THE LIKE Clarence B. Knudsen, Los Angeles, and James L. Bu ie, Sun Valley, Califl, assignors to Hoffman Electronics Corporation, a corporation of California Application September 4, 1953, Serial No. 378,614

6 Claims. (Cl. 123-448) This invention pertains to improvements in ignition systems such as are used with internal combustion engines. More specifically, the invention has to do with improvements applicable to the ignition systems of relatively small and lightweight engine generators utilized as power supplies for portable or field use, such as in signalling or communication work. However, the principles of the invention may also be utilized in larger equipments where desired.

The problem of producing a highly etficient yet highly compact portable power supply has received considerable attention, especially as a result of the ever-increasing communication needs of both military and commercial organizations. The principal source of power for these purposes has been the electric battery, either of primary or secondary type, although manually powered generators have found some limited use, as in emergency radios for life rafts and the like. Batteries, however, are rela tively bulky for any appreciable power drains, and have limited shelf-life which does not recommend them for use in remote areas or in emergency or stand-by service. For these reasons, considerable effort has been made to develop reliable and compact generators powered by internal combustion engines. These have been fairly successful in units of moderate and large capacity, such as of the order of 1000 watts or more, but really portable units (of the order of 100 to 1000 watts) have not been forthcoming.

One of the difficulties inherent in previous approaches has been in the necessity for providing for electrical ignition of the fuel mixture in a very small engine generator. Such a unit must be manually cranked .(to avoid the need for a starting battery), and its ignition, even when starting, must also be independent of a battery supply. On the other hand, manual cranking means slow starting speeds, and low energy output from a magneto or from the main generator. A magneto, if used, represents wasted space and weight since it performs no useful service (except during the starting phase) which cannot equally well be supplied by the main generator after running speed has been attained.

A particularly compact form of small-capacity engine generator employs an alternating-current generator of the rotating permanent magnet type, direct-connected to a small gasoline engine. The voltage output of such a unit will most conveniently be of the order of 120 volts or so, for direct use (as in lighting) or for conversion or rectification for powering telephone and radio equipment and the like. The output voltage of such a unit is very low at cranking speeds, and if transformation is attempted for purposes of starting ignition, the output is grossly excessive at running speeds. Either a complex and inefficient switch or regulator must be provided, or a con siderable power waste (by diversion from the output of the entire unit) must be tolerated.

The present invention provides a novel solution to this problem, and permits self-ignition which is adequate for starting and not wasteful of power at running speeds.

The invention will best be understood from the following detailed specification of a preferred embodiment, taken in connection with the appended drawings. However, the embodiment shown and described is merely exemplary, and may be modified in various respects without departing from the scope of the invention as defined in the appended claims. In the drawings,

Fig. 1 is a diagrammatic view showing a preferred form of the invention, and

Fig. 2 is a graph showing certain speed-voltage relationships referred to herein.

Referring now to Fig. 1 of the drawings, reference numeral 10 designates generally an internal-combustion engine which may be of any known or conventional design, utilizing a high-tension spark plug 12 for igniting the combustible charge in its cylinder. Theshaft of engine 10 is connected, either directly or through gearing or the like, with the rotor of an alternator 14, herein of the permanent magnet type rotating within a field winding structure to induce therein a voltage in well known manner. The current output of alternator 114 is available for use at terminals 16, and is also connected by conductors rotation of the engine shaft as by a cam 22 on or con-.

nected to said shaft. For a single cylinder, two-stroke cycle engine, as shown, having a single spark plug, the' points 20 may be arranged to remain open for say 330 of engine rotation, and to close for the remaining 30.

The invention does not depend upon rapid opening of the contacts, as does the ordinary induction coil system.

Since the present invention is principally intended for use near communication gear, shielding of the electrical parts is desirable. For this and other reasons, it is preferred to house the parts now to be described in a metallic shielding container designated by numeral 24. For clarity, the container is shown enlarged, and the drawing is intentionally out of scale in this respect.

The conductors 18 enter container 22 through conventional feed-

through capacitors

25, 26 provided to reduce transmission of radio-frequency noise over those conductors. The conductors then pass to the; primary winding 23 of an iron-core regulating transformer 30 having the shunt leg 32 containing an air-gap 34 dimensioned to saturate in a known manner to provide a desired nonlinear transformer characteristic as will be described. The capacitor 36 is shunted across the primary winding 28 to compensate for the lagging power factor of transformer 30.

The regulated output voltage of transformer 30 appears across its secondary winding 38, one terminal of which is connected to shield or container 24 and to the engine block (or otherwise) to one side of spark plug 12. Capacitor 40 is shunted across secondary 38 and (it being remembered that the alternator frequency will be lower at low speed than at normal running speed) has a value such as will approximately resonate the secondary winding 38 at the low frequency generated at the starting phase. A rectifier, such as a dry disc rectifier 42 is in series with the circuit to ignition (high tension) transformer primary winding 44, the circuit being completed periodically through contact points 20 as described above. A capacitor 46 is connected to be charged, through recti- Patented Nov. 27, 1 956 fier 42, during the relatively long intervals when contacts 20 are open, and the rectifier prevents it from discharging through winding 38 during periods of reduced or reversed value of the alternator voltage.

When contacts 20 are closed by cam 22, capacitor 4-6 discharges through primary winding 44 of the conventional ignition or spark transformer 48. The core may be connected to the start end of the secondary or high voltage winding 50 wound on the core, with the primary wound over the secondary and suitably insulated. The value of storage capacitor 46 is chosen to provide maximum energy transfer to primary Winding 44, and this produces the required voltage in secondary 50 for operation of the spark plug 12.

Fig. 2 illustrates by curve A the linear relation between engine speed and alternator output, and shows that for adequate voltage output (for ignition purposes) at running speed the value at starting (cranking) speeds would be Wholly inadequate. The non-linear characteristic of saturable transformer 30, in combination with

capacitors

36 and 40, effectively raises the voltage output at starting to a value which may be greater than normal for full running speed, and which is maintained at nearly that level even at full speed. In any event, it is plain that adequate voltage for ignition is available at the relatively low alternator speed obtained during the cranking operation. A somewhat higher-than-average ignition voltage is preferred for starting, as the engine, and the combustible charge, are apt to be cool, and the drooping characteristic provides this feature, as well as reduces the ignition-energy drain from the useful power output under running speed conditions.

In the form shown, the cam 22 is shown on the engine shaft, but it may be at the other end of the common shaft, or elsewhere. Also, spark plug 12 may be in a separate shield structure from that enclosing the ignition regulator components, as may be the cam and contacts 20. In such respects, the design may be varied widely to conform'to special requirements. These and other modifications may be made without departing from the invention claimed. By other suitable changes, the invention may obviously be applied to multi-cylinder engines, or to engines of other than two-stroke cycles.

It will be seen from the foregoing that the system provided is quite simple, in that a conventional. simple set of contacts 20 are employed, rather than a combined make-break set, for charging and discharging the storage capacitor. Also, the system provides for automatic reduction in the ignition power drain when running speed is attained, without any manual or centrifugal switch being required. Contact protection (such as the usual shunt capacitor) is not required, as contacts 20 open only after the storage capacitor is substantially discharged and only a low voltage, if any, then appears across the contacts. The rectifier 42 is simple and reliable, since it receives only the relatively low voltage applied to capacitor 46 across the primary of the spark transformer. The system operates well with alternators having sine-wave output, so that no compromise is required in the alternator design with respect to its useful output waveform.

What is claimed is:

In combination, an alternator having output terminals and an internal-combustion engine mechanically coupled to said alternator and including an ignition system, said ignition system including a regulating transformer having a pair of input terminals coupled to said alternator output terminals and a pair of output terminals, a rectifier and a storage capacitor serially connected across said regulating transformer output terminals, an ignition transformer having primary and secondary Windings, and a contact maker, said primary of said ignition transformer and said contact maker being electrically connected in series across said storage capacitor.

2. The combination according to claim 1 in which said alternator and engine are inter-coupled by a shaft which also actuates said contact maker in predetermined time capacitor intercouples said output terminals of said regulating transformer.

4. The combination according to claim 3 in which said capacitor resonates the output winding of said regulating transformer at a frequency corresponding to the starting speed of said alternator.

5. The combination according to claim 1 in which said regulating transformer includes a saturable core.

6. An ignition system for use with an internal-combustion alternator combination, including a regulating transformer having a pair of input terminals adapted for connection to the output terminals of an alternator and a pair of output terminals, a rectifier and a storage capacitor serially connected across said regulating transformer output terminals, an ignition transformer having primary and secondary windings, and a contact maker adapted for mechanical coupling to an engine driving an alternator, the primary of said ignition transformer and said contact maker being electrically connected in series across said storage capacitor.

References Cited in the file of this patent