GB608556A - Improvements in or relating to free-piston compressors - Google Patents

Abstract

608,556. Regulating compressors. PESCARA, R. P. Feb. 26, 1946, No. 6041. Convention date, Jan. 13, 1945. [Class 8 (i)] [Also in group XXVII] A method of regulating the output of a compressor having a free piston assembly including an integral engine and compressor piston, the engine 'piston controlling ports in its cylinder, comprises controling 'the delivery of tlae compressor in a first stage of regulation in which the maximum pressure in the compressor is approximately equal to the output pressure, by reducing the strake of the pistons from maximum stroke corresponding to maximum output to minimum stroke which is just sufficient for the pistons to clear the ports, which stroke corresponds to an intermediate output and further controlling the delivery in a second stage of regulation in which the stroke is kept constant at this minimum value and the maximum pressure in the compressor is increased above the output pressure. The Figure shows an opposed-piston free-piston compressor having working pistons 31, 32, connected respectively to a compressor piston 4 and a cushion piston 11. A fuel pump 22 supplies a fuel injector 2 in the working cylinder 1 in which the pistons 31, 32 operate. The compressor piston 4 compresses air at its inner side 52 which is used as scavenging air in the engine while on its outer side 51, it compresses air to be delivered by the compressor which passes by a chamber 13, conduit 14, to a reservoir 15. The fuel supply to the engine is controlled by controlling the delivery of the pump 22 by a pressure-responsive capsule 23 which is acted on by the pressure in the pipe 14 on the compressor side of a throttle valve 16. The position of the throttle valve 16 is controlled by the output pressure in a reservoir 15. During the period of operation from maximum output corresponding to maximum stroke to the output corresponding to minimum stroke, the throttle valve is kept open. Below this output the pressure in the reservoir 15 increases to an extent sufficient to close the throttle valve. This increases the pressure in the reservoir 13 and reduces the output of the compressor. At the same time, increase in pressure in the pipe 14 moves the fuel control into a position in which a rod 28 of the capsule contacts a plate 29 operated on by a spring 27. The fuel control then operates in dependence on the pressure in the pipe 14, to keep the stroke constant at the minimum value. To prevent excessive pressure in the chamber 13 and leakage past the throttle valve into the chamber 15 at low outputs, a relief valve 34 is provided. The chamber 15 has a relief valve 30 which allows the air to escape at pressures above a certain value and a shutoff valve 31 which shuts the reservoir off if the pressure falls below a certain lower minimum value. The valve 31 is controlled by a capsule 32 connected to the compressor delivery pipe. In a modification, regulation is carried out by replacing the throttle valve 16 by a valve which is closed for a number of strokes to cut off the compressor altogether, the valve being controlled by the pressure in the chamber 15 and a snap-acting device. In an alternative, the valve may be replaced by means adapted to lock the delivery valves of the compressor in the closed position. The various valves may be operated by servomotors instead of being operated directly.