Patent GB-717676-A (GB)
Title: Improvements in electrical ignition systems
IPC: F02P7/03
Filed: 1951-03-12
Abstract: 717,676. Condenser arrangements. BENDIX AVIATION CORPORATION. March 12, 1951 [March 15, 1950], No. 5934/51. Class 38(4) [Also in Group XXVII] In an ignition system comprising a sparking plug 36, a first condenser 45 or 48 which is charged to a voltage below the normal breakdown-voltage of the plug 36, and a second condenser 32 of considerably smaller capacity than the first condenser and which is charged to a voltage considerably higher than that of the charge on the first condenser the latter is charged through a first transformer 42, 43 and the second condenser 32 is charged through a second transformer 28, 29, the electrical constants of the charging circuits being such that during the same intervals of operation the first condenser is charged to a lower voltage than the second condenser irrespective of voltage variations in the power source. The system which may be connected to the battery 10 or other D.C. energy source through a selector switch 12 is provided with a solenoid-operated isolating-switch 14 remotely controlled by a manual switch 116. To prevent the system from interfering with radio and other circuits energized by the battery a filter is employed comprising a choke 16 and condensers 17 ... 20, the battery end of the filter being placed in a screened compartment. About 10-15 per cent of the battery current flows from power line 24 through a variable resistance 27 into the transformer primary 28, the circuit being intermittently connected to earth by an electromagnetically-actuated vibrator 22 thereby energizing the secondary winding 29, the increments of energy from which pass through a half- or full-wave rectifier 30 and are stored in condensers 32 at a voltage of between 5-7,000 the charging circuit being completed through a condenser 62; a sealed spark gap 33 is connected to earth between a rectifier 30 and condenser 32, the other terminals of the latter being joined to the primaries of ignition transformers 34, 35, the secondaries of which each have one terminal connected to a main or after burner or combustion chamber sparking plug 36 of a jet or reciprocating engine, there being two plugs associated with each burner or combustion chamber. The sparking rate of the plugs 36 is determined by the rate at which the condensers 32 are charged to a high enough voltage to break down gap 33; the condenser charge rate is dependent upon the battery voltage and in order to effect a consistent sparking rate the core reluctance of transformer 28, 29 is so selected by adjusting two air gaps therein as to cause the transformer to operate over the knee of the BH curve throughout the range of voltage variation. The major portion of the battery current travels through a resistance 39 to the centre tap 40 of the transformer primary 42, the outer ends of the latter being connected to upper and lower contacts of the vibrator 22; the interrupted D.C. flows alternately in opposite directions through the two halves of the winding and induces a voltage of alternating polarity in the transformer secondary 43 so alternately charging the condensers 45, 48 with small increments of energy through half-wave selenium rectifiers 44, 46 and 47, 49 respectively, up to full capacity at a low voltage viz. 600-1,000 volts. The terminals of condensers 45, 48 are connected between earth and one end of the secondary windings 35 via switches 52 and 53 so that when the gaps of sparking plugs 36 are ionized by the high frequency, high-voltage impulse from condensers 32 a high-energy low-voltage discharge is effected across the plugs by condensers 45, 48. To ensure that the latter condensers are fully charged between successive discharges of condensers 32 the transformer 42, 43 is constructed to operate in unison with transformer 28, 29 by arranging air gaps in the core thereof, so that the transformer works over the knee of the BH curve; furthermore, since resistance 39 limits the current carried by the vibrator contacts, a greater magnetization current is drawn by primary 42 and there is an increased voltage-drop across the resistance 39 as the source voltage rises from minimum to maximum so decreasing the voltage-drop that would otherwise occur across the primary. Small variations in the sparking rate may be effected by adjusting resistances 27. By operating remotely-controlled solenoid switches 52, 53 the low-voltage system is connected to the after-burner transformers through lines 54, 55, the switch terminals being bridged by condensers 56, 57 so that the high-frequency circuits to both the main and after-burner plugs 36 are always completed and ionization of all the plugs will occur whenever spark gap 33 conducts. If only two plugs are used the switches 52, 53 are dispensed with; if only one plug is to be energized then only one condenser 45 or 48 need be used, in which event it would be connected with secondary 43 through a full-wave bridge-rectifier. To ensure that the voltage attained by condensers 45, 48 does not vary substantially over the range of battery voltage a solenoid or cut-out 63 closes a switch 64 upon a given voltage appearing across the solenoid coil 63 and so connects a resistance 65 between earth and the resistance 39 and primary 42. In a modification, a spark gap is located between the high-energy condensers and ignitiontransformer secondaries to prevent leakage of the condensers during the charging period should the plug gaps become shunted by carbon or otherwise fouled. The spark gaps in the circuit may be replaced by circuit breakers or electronic tubes with triggering means. The electrical values of the components are given.