GB1355099A - Free piston engine - Google Patents

Abstract

1355099 Free piston IC engines A BRAUN 18 Aug 1971 [24 Aug 1970] 38809/71 Heading F1B A free piston engine comprises sensing means including two relatively movable members, one movable with the piston and the other positioned independently of the piston position, and operable upon relative movement to produce a signal dependent in value upon a characteristic of the relative movement, and control apparatus responsive to the signal to cause operation of the means (e.g. spark plug and/or fuel injection pump) for causing combustion at an instant when the signal value changes by a predetermined amount as a result of the piston slowing down near the end of the compression stroke. When the engine piston 20, Fig.2, moves to the right on its compression stroke, an auxiliary piston 54 coupled to it correspondingly moves to the right to compress air within a chamber 64. Since there is a leakage from the chamber 64 via an adjustable orifice 90 and a conduit 92 to atmosphere or to some other source of reference pressure, the pressure attained in the chamber 64 increases as the speed of the piston 54 and therefore of the engine piston 20 increases, reaching a maximum when the speed reaches a maximum. When the piston speed, and therefore the pressure in the chamber 64, has increased sufficiently, the force of a spring 84 is overcome and a piston 70 is moved to close ignition contacts 112. Near the end of the compression stroke, when the piston speed, and therefore the pressure in the chamber 64, has decreased sufficiently, the spring 84 forces the piston 70 to the right and the contacts 112 open to cause ignition. The timing of the ignition in relation to the top dead centre, which is adjustable by means of the adjustable orifice 90 and an adjustable spring abutment 80, therefore depends on a sensing of the speed of the piston 20 as it approaches top dead centre and is independent of the length of the stroke, and therefore position of the top dead centre, which varies according to the load imposed on the engine and also upon the occurrences of misfire. Compensation for misfires can be improved by providing, in addition to the bleed from the chamber 64 via the orifice 90, a further bleed via a slide valve (144), Fig.3 (not shown), operated by a spring-loaded piston (150) subjected to the pressure in the chamber 64. A reduction in the pressure reduces the opening of the valve (144). In another modification, the orifice 90 is replaced by a valve 161, Fig.7, operated by a cam 168 on the piston rod through a telescopic device 162 comprising a spring-loaded piston 178 within a cylinder 172 of substantial mass. If the engine piston is moving slowly to the right on a compression stroke, the piston 178 and cylinder 172 move upwardly as a unit to transmit movement from the cam 168 to the valve 161. At higher piston speeds and consequently higher piston acceleration, the inertia of the cylinder 172 prevents it from moving with the piston 178, and the piston 178 moves upwardly within the cylinder 172, air being expelled through a check valve 183. This temporarily alters the relationship between the position of the cam 168 and the opening of the valve 161. Subsequently, the piston 178 returns slowly to its normal position within the cylinder 172, air being bled back through an adjustable orifice 184. This arrangement advances the ignition at higher speeds. In another arrangement for adjusting the ignition timing in accordance with speed, the operation of the ignition contacts is effected through a diaphragmtype dashpot, Fig.8 (not shown), which retards the opening of the contacts. The chamber 64 may be provided with an air bleed which is controlled automatically in accordance with the delivery pressure of the compressor 23 driven by the engine, the air bleed being closed at low delivery pressure indicative of e.g., a misfire.