GB1357957A - Free piston engine - Google Patents

Abstract

1357957 Free piston engines A BRAUN 18 Aug 1971 [24 Aug 1970] 38808/71 Heading F1B A free piston engine comprises sensing means arranged to generate an electric signal at an instant and with a magnitude dependent upon a characteristic of the movement (as distinct from position) of the piston and an electrical control circuit controlling operation of the means (e.g. spark-plug and/or fuel injection pump) for causing combustion. The piston velocity of the engine is sensed by a stationary coil 28, Fig. 2, traversed by a permanent magnet carried by the piston-rod. An adjustable proportion of the voltage generated in the coil 28 is applied via a potentiometer 34, 38 to a Schmitt trigger 83. During the compression stroke, the passage of the magnet past the coil 28 generates a voltage which switches on the Schmitt trigger, thereby producing a negative step in the collector voltage of a following amplifier 88. The resultant negative pulse transmitted by a capacitor 96 is suppressed by a diode 100. Near the end of the stroke, the reduction of piston velocity causes the generated voltage to decrease to a value at which the Schmitt trigger is switched off. The resultant positive pulse transmitted by the capacitor 96 triggers a thyristor 112 into conduction in a capacitor-discharge ignition circuit to provide spark ignition. Adjustment of ignition timing is effected by variable resistor 34. During starting, when the piston velocity is insufficient to generate a high enough voltage to operate the Schmitt trigger, operation of the latter may be effected by the circuit modification shown in Fig. 7. A stationary reed switch 136, closed during a portion of each stroke by a magnet moving with the piston discharges a capacitor 134 through the base of a transistor 60 having its emitter and collector connected in parallel with those of the first transistor 50 of the Schmitt trigger 83, thereby switching on the Schmitt trigger. When the switch 136 is switched off, the capacitor 134 re-charges through a resistor. At normal engine speed, there is insufficient time during each stroke to charge the capacitor 134 to a high enough voltage to operate the Schmitt trigger, which reverts to normal operation. As a further aid to starting, the resistor 38, Fig. 2, may be of a high enough value to provide sufficient voltage at starting to operate the Schmitt trigger, another resistor (166), Fig. 13 (not shown), being switched into parallel with the resistor 38 during normal running to provide the normal voltage, this switching being effected by a transistor (162) in series with the resistor (166) and rendered conductive by a voltage applied to its base, this voltage being generated by the engine and having the required amplitude only at normal running speed. In a further modification, a resistancecapacitance network and a diode are connected in series with the coil 28, whereby a negative bias is built up during normal running to reduce the net voltage available for operating the Schmitt trigger, the full voltage generated in the coil being available at starting.