Patent GB-1313392-A (GB)
Title: Device comprising two coaxial elements of which one is reciprocable within the other
IPC: F16J3/06
Filed: 1970-04-14
Abstract: 1313392 Pistons PHILIPS GLOEILAMPENFABBIEKEN NV 14 April 1970 [17 April 1969] 17667/70 Heading F2T [Also in Division F1] A hot-gas engine, cold-gas refrigerator, coinpressor or other device having a rolling diaphragm seal which is arranged between two coaxial elements one reciprocable within the other and between a first space 4 containing gas and a second space containing a liquid for supporting the rolling diaphragm comprises control means 23 for maintaining a constant pressure differential across the rolling diaphragm, and an annular seal interposed between the rolling diaphragm and the first space to provide a third space containing gas, the seal having a mean diameter which is equal to the effective diameter of the rolling diaphragm. The hot-gas engine shown has a working space formed by a compression space 4 and an expansion space 5 which communicate with each other via a cooler 6, regenerator 7 and heater 8. The piston 2 and displacer 3 are mounted on rods 9 and 11 respectively and are arranged to reciprocate with a phase difference connected to a rhombic drive mechanism 13 in a crankcase 14 containing lubricating oil. Between the piston 2 and the cylinder and between the piston and the displacer rod are arranged rolling diaphragms 16, 18 and piston rings 24, 25 which separate the first space 4 from third spaces 16, 19 and second spaces 17, 20, the spaces above and also below the rolling diaphragms being in communication with each other through horizontal ducts. Lubricating oil is continuously supplied to the spaces 17, 20 by a pump 22 and by means of a pressureoperated control valve 23 is allowed to leave the spaces at a rate such that a constant pressure differential is maintained across the rolling diaphragms. The piston rings 24, 25 are provided with radial grooves 24c, 25c on their upper faces and act as non-return valves to establish a pressure in the spaces 16, 19 equal to the minimum pressure occurring in the compression space 4; the arrangement ensures that a sudden pressure increase in the compression space would not affect the diaphragms. In a modification of the hot-gas engine shown, the piston (2) is extended to enclose a buffer space (27) below the compression space (4) and instead of a pump 22, pumping rings (29, 30) are arranged on the lower part of the piston for pumping the oil to the spaces below the rolling diaphragms. In alternative arrangements, the radial grooves may be provided on the faces opposite to that shown or replaced by ducts in the piston or adjacent parts and the piston rings can either be housed in the cylinder and displacer rod instead of in the piston or replaced by a seal formed by a narrow gap between the respective surfaces so that the pressure in the spaces 16, 19 will be equal to the mean pressure in the compression space 4 or buffer space (27). In a compressor in which the minimum pressure occurring in the compression space is atmospheric, the diaphragms are kept taut by providing the grooves on the lower faces of the piston rings to establish a pressure in the spaces above the diaphragms equal to the maximum pressure occurring in the compression space. It is also possible to have an arrangement in which the diaphragms are inverted so that their concave sides face the gas-filled spaces above the diaphragms.