Low-speed compensated ignition system for an internal combustion engine

Claim 1

Low speed compensated ignition system for an internal combustion engine, adapted for connection to a source of electrical power (1) having an ignition coil (5, 6, 42); a controlled switch (7, 9) serially connected with said coil and controlling current flow therethrough; means (8) sensing current flow through the ignition coil and deriving an electromagnetic storage signal; a control signal generator (16) operating in form of an a-c generator and providing undulating signals in synchronism with the revolutions of the engine which have a positive peak value (Us) and a negative peak value (Uo) and a zero or null or center or cross-over line upon change of polarity of the signal; a control circuit including a threshold switch (13) connected to receive the undulating signal connected to and controlling said controlled switch (7, 9) when the undulating signal is above the zero or null or cross-over level and is increasing in a positive direction from the negative peak value (Uo) and reaches, with respect to said zero or cross-over level, a first ON threshold level (Ue) to store electromagnetic energy in the coil, and interrupting conduction of the controlled switch (7, 9) and thus initiate release of electromagnetic energy from the coil to initiate an ignition spark pulse when the undulating signal is decreasing from a positive peak value (Us) and reaches, with respect to said zero or cross-over level, a second OFF threshold level (Ua), said control circuit being further connected to receive the electromagnetic storage signal to modify the response of the threshold switch in dependence on sensed current flow through the coil by shifting response to said threshold switch with respect to the change in polarity of the signal, and hence modifying the zero or null or cross-over level of the undulating signal as applied to the threshold switch, and comprising means for additionally modifying the ON threshold level with respect to the modified zero or null or cross-over level of the undulating signal under low-speed conditions to prevent excessive current flow through the coil including circuit means (36, 37, 38, 39, 19) responsive to low-speed conditions of the engine and hence of the control signal generator connected to said threshold switch (13) for introducing to said threshold switch an additional modifying signal affecting the first ON threshold response level thereof in a direction to delay response of the threshold switch and thus shorten the duration of conduction of said controlled switch (7, 9) and hence the duration of current flow through the coil (5, 6); wherein said control system includes a circuit network (26) of variable conductivity connected (20, 21) to a terminal of said threshold siwtch (13); the auxiliary capacitor (36) is connected to said terminal (inverting) of the threshold switch, said control signal generator (16) having one of its terminals connected to said terminal of the threshold switch; and wherein the charging circuit for said auxiliary capacitor includes a serial resistor (37) diode (38) connection from said one terminal of the control signal generator (16) connection to the circuit network of variable conductivity (26); and a coupling and calibrating resistor (39) is provided connected between the charging circuit connection and said auxiliary capacitor and said terminal of the control signal generator (16), to interconnect said control circuit, said circuit network of variable conductivity and said auxiliary capacitor and provide for modification of the response of the threshold switch (a) in accordance with the zero or null or cross-over of the undulating signal derived from the control signal generator, as modified by the circuit of variable conductivity, and (b) modification of the response threshold level of said threshold switch as modified by the auxiliary voltage applied by the auxiliary capacitor (36) and derived from said control signal generator.