US2879451A - Low tension ignition system - Google Patents

Description

E. T. SHERWOOD ETAL 2,

LOW TENSION IGNITION SYSTEM March 24, 1959 Filed Ma 4. 1953 fill N ('0 V H II ATTORNEY United States Patent "ice LOW TENSION IGNITION SYSTEM Edwin T. Sherwood, Bayside, and Herbert C. Ganiere,

Milwaukee, Wis., assignors to Globe-Union Inc., Milwaukee, Wis., a corporation of Delaware Application May 4, 1953, Serial No. 352,742

5 Claims. (Cl. 315-214) This invention relates to improvements in ignition systems, particularly to systems including low tension spark plugs.

Such systems must develop spark gap voltages in the neighborhood of 1000 and cause a spark to jump a gap of about .010 inch or under with a current discharge of approximately 400 amperes in the short time of A to 1 microsecond. Systems of this type employ a storage capacitor which is first charged from a source of unidirectional voltage and then discharged to the plug. However, the presently known systems are limited and unsatisfactory because they cannot charge the storage capacitor fast enough for use with modern high speed combustion engines and require an uneconomical amountof input energy in order to accomplish the required output. Some of such systems employ a high frequency source in series with the plug. This cuts down the amount of effective amperage which will jump the gap at each discharge and otherwise lessens the efiiciency of the spark produced.

It is an object of this invention therefore to provide a low tension ignition system which will meet the requirements set forth above without such disadvantages and which may be economically manufactured and easily installed for use.

This object is obtained by linking a primary circuit to a secondary circuit by a toroidal core with an air gap and breaking the primary circuit only once for each discharge of a storage capacitor in the secondary circuit.

The air gap sufiiciently increases the rate of current buildup in the primary circuit so that the system may be used with speeds up to 20,000 pulses per minute. Such gap also increases the amount of energy that may be stored in the magnetic field. The air gap also contributes to the increase in the rate of charge of the storage capacitorin the secondary circuit by the resulting increase in rate of collapse of the magnetic field and increase in the natural frequency of the secondary circuit.

The novel features, which are considered characteristic of the invention, are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof,

will best be understood from the following description of a specific embodiment when read in connection wi the accompanying drawings, in which:

Fig. 1 is a schematic diagram of an ignition system embodying the present invention; and

Fig. 2 is a sectional view taken on the line 22 of=-" connected to a current limiting resistor 12 which, together with the primary winding, has an approximate value of 5.6 ohms. This value permits this system to operate up to 5000 pulses per minute. To increase this rate to 20,000 pulses per minute, this value must be reduced to approximately 1.1 ohms so that the primary current may i build up to the saturation value in the shorter time available. Such resistor serves to limit the current flow in the primary circuit to a value sufficient to saturate the core of the transformer. Its value will therefore be dependent upon the characteristics of such core. The drain on the battery is thus sufficiently limited and an essentially constant output voltage may be obtained even at high speed operation of the system. The resistor 12 is connected in series with the primary winding 14 of the transformer. This winding is connected to the negative terminal of the battery 10 through breaker points 16. These points have a spark suppressing capacitor 18 connected across them. The negative side of the primary circuit thus established is connected, to the ground as indicated at 20. It is advantageous to use a gap of about .022 inch at the breaker points 16. These points must open as rapidly as possible and remain clean in order to prevent the development of an arc across such points when they break. In this connection the capacitor 18 has a rating of approximately 0.5 mf. (micro farad). This capacitor, together with thequick, clean breaking of the breaker points 16, cooperates to prevent an are from developing across such points in spite of the high induced voltage developed in the primary winding 14 by the rapid collapse of the magnetic field. The elimination of such arcing is important because an arc would consume some of the energy in such magnetic field and would thereby reduce the voltage developed across the storage capacitor. The breaking points 16 are controlled by a cam 22 which provides rapid opening and closing characteristics. The cam 22 rotates in counterclockwise direction and the break or opening takes place at the slope 24 located about ahead of the closing of the circuit from the storage capacitor to the spark plug. These breaker points will be closed by the slope 26 about 3 after such circuit has been closed.

An alternative primary circuit may include a capacitor which is first charged from the battery andthen discharged through the primary winding by a cam operated switch. Another variation of the primary circuit maybe the inclusion of a circuit breaker which would open a circuit to the primary coil 14 at the instant the primary current reaches a value sutlicient to saturate the transformer core. It may also be advantageous to placea control switch in the primary circuit which will open when speed becomes zero and which, responsive to speed, shorts out part of the resistance 12. Such automatic breaker points and control switch do not change the basic operation of the circuit but function primarily to conserve the energy drain.

The secondary circuit will now be described. It includes in series, a secondary winding 28, a rectifier 30, and a storage capacitor 32. This rectifier may be of germanium'cell type connected for half wave rectification. However, a gaseous type hot or cold cathode unit may be used. The storage capacitor has a capacitance of 0.1 mf. and a test voltage of 2000 volts. It should be substantially non-inductive with low absorption and must be capable of discharging at high rates. In operation, it is normally charged to a voltage of about 1100.

The spark plug circuit into which the storage capacitor 32 discharges will now be described. Oneside of such storage capacitor is connected to the ground at 34 and the other side thereof is connected to breaker points 36 which are in turn connected by a distributor 38 to the center terminal of a spark plug, the gap of which is indicated at 40. The outer electrode of such plug is connected to ground as indicated at 34. The breaker points 36 are coordinated with the breaker points 16 by a cam 42 operated from the same shaft 44 as the cam 22. The cam 42 has a lobe 46 which is positioned so as to close the breaker points 36 approximately 3' position.

ii-stream before the closing of the breaker points 16 and open 'such points within 30 after closing. While only one plug is illustrated, this system may be used with mult ple cylinders. In such case, the distributor 33 has other conventional contacts to connect the desired plugs in proper order with the secondary circuit breaker points 36. This is accomplished by connecting the distributor 38 m the shaft 44 by a conventional reducer 48. In anyarrangement of cylinders, the storage capacitor 32 rsfirst charged and then discharged for each arcing of each gap. The voltage of 1100 at the capacitor 32 is sufficient to ionize the gaseous fuel at the gap of .a low tension-sparkplug, if such plug gap is .010 inch 'or under as described and claimed in the application of George "D. Suter co-pending herewith. Such ionization will take place in normal operating conditions without the necessity of conductive material on the surface of the insulating material defining such gap. The energy stored incapacitor 32 is dissipated in the ionized gap in the relativelyshort time of V2 to 1 microsecond, during which time a peak current of about 400 amperes is attained. a v i :The primary circuit and the secondary circuit are linked by a novel form of toroidal type core 50. This core is made of laminationsjof oriented silicon steel about .014 inch thick (see Fig. 2). Enough laminations are used in this particular example to provide a cross-section of approximately /2 inch by 1% inches. The laminations are bent to make aging having an approximate mean diameter of 3 inches. However, this ring, unlike conventional rings, is not endless. Instead, it has spaced ends 52 forming an air gap of 0.25 inch effective length, which is maintained by an insulating spacer 54 of approximately .020 inch. This gap increases the rate of current build-up in the primary circuit so-that it may he .pulsed at rates up to 20,000 per minute. It also increases the amount of possible energy that may be stored in the magnetic field. Of course this energy will be ratable with the cross-sectional dimension of the core and the type of material used. The gap also increases the rate of charge of the storage capacitor due to the increase in rate of collapse of the magnetic field and the increase in the natural frequency of the secondary circuit.

In this particular example the secondary winding 28 consists of a thousand turns distributed over the entire length of the core 50. The primary winding 14 consists of a hundred turns wound over the secondary winding 28 and distributed over the entire length of the core. The primary winding thus tends to partially shield the secondary winding from radiating. The particular turn ratio of ten to one was selected to hold the voltage induced in the primary winding down to a value low enough to prevent arcing over the breaker points 16, having regard to the capacitance value of the capacitor 32. A smaller turn ratio would reduce primary current drain and therefore be more economical but would increase the danger of arcing at the breaker points 16 and would reduce the'maximum rate at which the system can operate.

The core 50, instead of being made from silicon steel, may be made of other materials, such as powdered magnetic materials in insulating type binders or ferro-ceramic materials.

As shown in Fig. 1 the system has just fired. As the shaft 44 continues rotation in timed relation with an engine, the breaker points 36 will open disconnecting the. storage capacitor from the spark plug circuit- The breaker points 16 will then close, causing a magnetic field to be set up in the 'core50. This field will reach its saturation point before the slope 24 reaches effective The amount of current used to obtain this saturation is limited as heretofore explained by the re sistance 12 so that no more current is used than is needed to" saturate such core. The breaker points 16 then open atslope 24 and the magnetic field in the core 50 collapses at a rapid rate. It is this rapid rate of collapse which induces a high voltage in the secondary winding 28, causing current to flow into the capacitor 32, charging it to a voltage of about 1,100 volts. This voltage is suflficient to ionize the gaseous fuel at the gap 40 which has a spark over voltage less than that thus produced by the storage capacitor 32. Within approximately after the breaker points 16 have opened, the breaker points 36 will be closed by lobe 46, the storage capacitor 32 will be connected to the spark gap 40, and its entire charge will be dissipated in-the gap in about /2 to 1 microsecond at a peak current rate of approximately 400 amps. The energy of this spark is much higher than that obtained from conventional high tension ignition systems and is sufiicient to ignite combustible materials, though under high compression, and keep the electrodes of the spark plug clean and free of damaging deposits. This ability to keep the electrodes of the plug clean is particularly advantageous for slow speed operation. With conventional ignition systems the plugs foul from overly rich mixtures at low speeds and short out when there is asudden demand for power. With this low tension system an overly rich mixture will be more completely fired and the plugs maintained clean so that when a load is placed on the engine the plugs will not fail to fire or properly ignite the increased charge. Although only one embodiment of the invention is shown and described herein, it will be understood that this application is intended to cover such changes 'or modifications as come within the spirit of the invention or scope, of the following claims. 'We claim: '1. vAn electric ignition system for causing a spark to jump a gap of about .010 inch at a voltage in the neighborhood of 1000 volts and a current discharge of approximately 400 amperes in the time within the range of /2 to 1 microseconds, comprising a source of uni-directional voltage under volts, a primary circuit connected to said source including a first breaker switch and a resistance of within the range of 1.1 to 5.6 ohms to permit the primary current to build up to the saturation value of a toroidal core electromagnetically linking said primary circuit to a secondary circuit in said range of time without excess flow of such current to limit the drain on said source, a secondary circuit including a rectifier and a substantially non-inductive storage capacitor with low absorption factor and capable of discharging within said range of time, said primary and secondary circuits being electromagnetically linked by a toroidal core with an air gap of about .025 inch effective length to provide a high enough rate of current build-up in said primary circuit to permit saturation of said core within said range of time, and a spark gap circuit connected with said storage capacitor by a second breaker switch coordinated with said first breaker switch so as to close and open said second breaker switch during the period the said first breaker switch is open to fire said spark gap circuit during the non-charging period of said primary circuit and close and then open said first breaker switch only once after said second breaker switch is opened and before again being closed to charge said primary and secondary circuits.

electrodes with each pulse, comprising,.a source of unidirectional voltage subjectto voltage drop upon undue drain, a primary circuit connected to said source ineluding a first breaker switch anda resistance sufi'icient to restrict the flow of current in said primary to an amount necessary to saturate the core of the transformer within the time required for a single pulse at said rate, a secondary circuit including a rectifier and a substantially non-inductive storage capacitor with 10W absorption factor and capable of charging and discharging with in said time, said primary and secondary circuits being electromagnetically linked by a toroidal core with an air gap small enough to provide a high enough rate of cur rent build-up in said primary circuit to permit saturation of said core within said time, and a spark gap circuit connected with said storage capacitor by a second breaker switch coordinated with said first breaker switch so as to only once charge and discharge said storage capacitor within said time.

5. An electric ignition system as claimed in claim 4 in which said first breaker switch opens approximately 34 of the time of a single pulse ahead of the closing of 6 said second breaker switch to accomplish the storage of energy in the field electromagnetically linking said primary and secondary circuits and closes of such time after the second breaker switch has closed, said second breaker switch remaining closed only for A of such time after the closing thereof.

References Cited in the file of this patent UNITED STATES PATENTS 349,611 Stanley Sept. 21, 1886 1,251,651 Espenschied Jan. 1, 1918 1,557,201 Hunt Oct. 13, 1925 1,598,486 Mallory Aug. 31, 1926 1,917,565 Williams July 11, 1933 2,478,672 Smits Aug. 9, 1949 2,571,788 Tognola Oct. 16, 1951 2,643,284 Putnam June 23, 1953

Images