Patent GB-898730-A (GB)
Title: Free piston machine
IPC: F02B71/04
Filed: 1960-11-14
Abstract: 898,730. Free-piston machines. BRAUN, A. Nov. 14, 1960 [Nov. 23, 1959], No. 39092/60. Class 7(2). A free piston machine comprises a rigid frame including a pair of axially aligned compressor cylinders and a combustion cylinder between the compressor cylinders, a pair of piston assemblies .each having a compressor piston disposed for reciprocation in one of the compressor cylinders and a power piston of a diameter not larger than that of the compressor piston disposed for reciprocation in the combustion cylinder, each power piston having a crown and a skirt and means supporting one of the piston assemblies for reciprocable movement comprising a guide shaft having a portion extending through one of the compressor pistons and into the crown of one of the power pistons, a first support fixed to the frame and engaging the guide shaft portion for direct support thereof by the frame at one point and a second support independently fixed to the frame in spaced relation to the first support and engaging the guide shaft portion for direct support thereof by the frame at a second point spaced from the first point. Referring to Fig. 1 the machine has a pair of compressor cylinders 1 which are supported in spaced axial alignment as by open frame members Z. The power or combustion cylinder 3 is supported on spider frames 4 each comprising a ring 5 fixed to the inner end of the cylinder 1. Annular chambers 20 form return or bounce energy chambers. In a modification no piston rings are employed on pistons 8 and 9. It is stated that since there may be no mechanical contact between the pistons and the cylinder walls there may be no necessity to lubricate either the combustion or compressor section and as a consequence no necessity for cooling. With the raising of the pressure in all chambers the size of the engine and particularly of the compressor pistons is decreased with consequent considerable increase in cyclic frequency which reduces any sealing problem between pistons and cylinders since the time available for gas to flow during any one cycle is decreased to an extremely low value. Fig. 4 illustrates an arrangement for providing flow of air from air receiving chamber 30 to bounce chamber 20 if at the innermost position of the piston assemblies pressure in the bounce chamber is below that in chamber 30. The arrangement comprises an axial bore 46 in the guide shaft 12 having a port 47 at its inner end communicating with the interior of piston 9 and a check valve 50. Fig. 5 shows an auxiliary bounce structure for use when additional bounce energy is required. Fig. 6 illustrates another type of auxiliary bounce structure. The compressor cylinder and cylinder head may be formed in one piece. Instead of arms 6 in the frame 4 a closed frusto-conical wall may be provided. Such an arrangement provides a closed chamber which can be employed as a negative bounce chamber. The construction may be such as to permit removal of the cylinder head and compressor piston from the engine while the power piston and frame 4 remain in place Arrangements for cooling the crown of the piston 9 and the member 18 are described. In Fig. 13 the guide shaft 93 extends axially through the cylinders 90 and 92 and has its ends supported in end walls 87. Further modified arrangements are shown in Figs. 14 and 15.