Patent GB-633863-A (GB)
Title: Improvements in power plant comprising internal-combustion-operated free-piston machines
IPC: F02B71/00
Filed: 1947-03-12
Abstract: 633,863. Gas-power plant ; starting ; regulating. PESCARA, R. P. March 12, 1947, Nos. 6947 and 6948. Convention dates, Feb. 5, 1946 and Jan. 10, 1947. [Classes 7 (i), 7 (v) and 7 (vi)] In a system including two free-piston generators of compressed gas, each of which includes a motor cylinder, a compressor cylinder, a free-piston assembly including a motor piston and a compressor piston adapted to co-operate with the cylinders respectively, an oscillatory-control member, means for subjecting the control member to the combined actions of the pressures in two corresponding chambers of the generators respectively, the last mentioned chambers having the same functions in the two generators and varying in volume as the free-piston assemblies reciprocate, so as to cause said pressures to vary periodically, there is provided means operable by the control members for influencing the frequency of operation of at least one of the generators automatically so as to restore a given phase difference between their operations ; the generators may be adapted to work at the same frequency but with a 180 degree phase difference ; means may also be provided for starting the generators with at least substantially 180 degrees phase difference. The two free-piston gas-generators 1, Fig. 1, exhaust into a common conduit 11 whilst scavenging-air casings 9 may be interconnected by openings 10. Cushion chambers 6a in each unit lead by way of conduits 13 of relatively large section into cylinder 13a and 13b containing a spring-loaded stepped-piston 12, whilst smaller pipes 14 branch from the conduits 13 into the other end of the cylinder. The oscillatorycontrol member 15, operated by the piston 12, controls intercommunication between the cushion chambers so that whilst the two gas generators remain 180 degrees out of phase, the difference in pressure on the piston 12 is insufficient to open the member 15. If one generator gets ahead of this phase opposition then the pressure difference in the respective cushion chambers causes oscillatory opening of the member 15. To ensure that the member 15 opens only in that part of the cycle when the pressure is higher in the cushion chamber of the generator which has moved ahead, than in the other generator, the leverage of a mass 18 attached to the piston 12 is made to depend upon the working pressure of the generators, which pressure is led to a cylinder 22 that controls the movements of the mass 18 so that the oscillatory piston 12 and member 15 are given a natural frequency equal to the speed of the free piston. A damping unit 27 is interposed between the mass 18 and the piston 12. In a modification, the piston 12 is not rigidly connected with the oscillatory member and these parts are given a natural frequency which is different from the speed of the free pistons. Further, the member permits communication between the cushion chambers for nearly the whole of the piston stroke, in one embodiment on the up and in another on the down stroke only. The connecting means between the piston and valve is frictional in one instance and hydraulic in another. In another modification, Fig. 10, the two cushion chambers are permanently interconnected and the pressure is taken by a conduit 32 to a cylinder 35, the spring-loaded piston in which has a restricted opening 34 and operates the control racks 41 of fuel-injection pumps 42. A rod 43 enables the fuel supply to be adjusted by hand or by the governor of a turbine fed by the generator. Each fuel-injection pump, which may be of the direct injection or accummulator type, is operated from a cam coaxial with a pinion 45 which together with racks 46 form the synchronizing mechanism. When one generator gets out of phase opposition with the others, the resulting pressure in the cushion chambers fluctuates and causes oscillation of the piston in cylinder 35 with a consequent increase in the quantity of fuel delivered to the leading generator and a decrease in fuel delivered to the lagging machine. With accumulator injection the fuel adjustment takes place during the first half of the " in " stroke, whilst with direct injection the adjustment occurs when the instantaneous pressure in the cushion chambers is about equal to the mean pressure, even when the generators are not in phase opposition. To start the generator, the free-piston assemblies are positioned as. shown in Fig. 12, the control handle 59 is set to position Y permitting compressed air from reservoir 56 to both act on a piston 51 and thereafter lock the free pistons in the outer position by holding latches 47, 48 in engagement, and enter cushion chambers 6a. Upon moving the control handle 59 to position X, the cylinder containing piston 51 of generator A is exhausted, the latches are disengaged by a spring and pressure which is taken to the cushion chambers 6a of the generator through pipes 65, 66, pressure-reducing valves 68 and check valves 67 causes the generator to start. Due to check valves 57 generator B is not similarly started until the freepistons of generator A reach their inner positions and a cam 62 on the pinion 45 of the synchronizing mechanism opens a valve 61 and permits the air in the cylinder of piston 51 of generator B to escape to atmosphere. The two generators are then started in phase opposition. The pressure in the cushion chambers of generator A may be used in place of cam 62 to control the starting of generator B. In a modification in which the cushion chambers of the two generators are permanently connected, the freepiston assemblies may be started simultaneously, or at least not in phase opposition, this latter state being subsequently obtained by any of the means previously described. Specifications 561,536 and 595,297 are referred to.