Patent GB-722793-A (GB)
Title: Improvements in plant comprising devices for keeping a given phase relation between at least two internal-combustion operated free piston machines of the plant
IPC: F02B71/00
Filed: 1950-05-18
Abstract: 722,793. Plant comprising free-piston machines. SOC. D'ETUDES ET DE PARTICIPATIONS EAU, GAZ, ELECTRICITE, ENERGIE SOC. ANON. May 18, 1950 [May 28, 1949], No. 12532/50. Classes 7 (1) and 7 (2). In a plant for supplying a fluid under pressure including at least two internal-combustion operated free piston machines intended to work in given phase relation to each other under control of a phase relation maintaining device which acts upon an adjusting device capable of varying the frequency of reciprocation of at least one of the free piston machines, this phase relation maintaining device being responsive to the difference of the pressures which exist in corresponding spaces of variable volume and filled with gas of the two free piston machines, the phase relation maintaining device acts upon the adjusting device through pressure impulses which correspond to the instantaneous pressure existing in both of the spaces just when they are at the same pressure. Fig. 1 shows a plant comprising two internalcombustion operated free piston gas generators A, B, supplying gases under pressure through a common exhaust pipe 10. In order to keep to a minimum pressure variations in a common scavenging air reservoir 9 and/or in the exhaust pipe 10 it is necessary to keep the phase difference between the pistons 4 of the generators equal to 180 degrees. In the plant shown this phase relation is maintained by controlling the pressures in the pneumatic energy accumulators 6a, 6<SP>1</SP>a of the generators. Fig. 3 is a diagram comprising a curve I showing pressure variations in the accumulator 6a against time (t) and a similar curve II showing pressure variations in the accumulator 61a. The phase difference between these curves in 180 degrees and at points Xa, Xb, Xc the pressures in the two. accumulators are equal to one another and have the value p. When the phase difference is altered for instance so that the curve I becomes the curve I<SP>1</SP> the points of intersection X<SP>1</SP>, X<SP>11</SP> of the curve I<SP>1</SP> and II showing moments when the pressures in the two accumulators are equal to one another correspond to different pressures p<SP>1</SP> and p2. On the outward stroke of generator A the pressure p<SP>1</SP> at which the pressures become equal is higher than p, and the pressure p<SP>2</SP> is lower than p. This fact is made use of in the plant of Fig. 1 in order to control'the phase relation between the generators. Thus the value at which the pressures in the two accumulators become equal (equality pressure) is employed to control the content of the pneumatic accumulators. This is effected as shown by means of a measuring member 12 and distributing member 13. The measuring member 12 is normally maintained in one of two end positions by the pressures in the accumulators 6a, 6<SP>1</SP>a but at about the moment at which the pressures in the accumulators become equal to one another the member 12 moves from one end position to the other and in doing this by means of a groove 18 momentarily connects for instance the accumulator 6a to a conduit 17. Thus the equality pressure is communicated to the conduit 17. The distributing member 13 is also operated by the pressures in the accumulators but due to a brake 33 its movement lags behind that of the member 12 and thus when the equality pressure during the outward stroke of the generator A is applied to the conduit 17 it can pass by way of a groove 24 in the member 13 into a conduit 31 and can act on a piston 47 connected to a valve 35 of the stabiliser of the accumulator 6a and adjust the pressure in the accumulator to such a value as to restore the desired phase relation between the generators. A similar action takes place on the outward stroke of the generator B and the contents of accumulator 6<SP>1</SP>a is adjusted in the opposite sense. Instead of both, one only of the generators may be acted on. The difference between the equality pressure and the average of the equality pressures may be used for control purposes. this average value being at least approximately equal to p. In a modification of this arrangement instead of the equality pressures acting on the pistons 47, 471, as shown, they may operate indirectly for instance simultaneously on a differential element which operates on the reciprocation frequency adjusting device of at least one of the machines or on opposite sides of a piston which is connected through springs and levers to the valves 35, 35<SP>1</SP>. In an alternative embodiment of the invention (not shown,) the equality pressures act on opposite sides of a piston which controls a valve which in co-operation with non-return valves allows air to flow from one accumulator to the other. The measuring member is downstream of the distributing member. One only of the generators may employ a stabilizer Figs. 6 and 7 show another embodiment comprising three generators A, B, C, which are maintained at a phase difference of 120 degrees with respect to one another. The scavenging reservoirs of the three generators are separate from one another but all three generators deliver into a common conduit 66. In this case the equality pressures when the desired phase difference is maintained are different so that only one of these pressures is used for control purposes. Thus the distributing member has one groove only 71 therein. The average of the impulse pressures which act on the front faces of the pistons is maintained below pistons 47, 471, 4711 connected to the stabilisers, Conduits 79, 79<SP>1</SP> and 79<SP>11</SP> of small cross section being provided for this purpose. Conduit 67 communicates with the cushion or cushions of the generator A. Instead of employing a brake for the distributer member restrictions 74, 75 are provided in the pipes leading to outer ends of the distributer cylinders. If one generator is cut out of action a cock 82, 821, 8211 associated therewith is turned anticlockwise through 90 degrees and the other two generators are then maintained at a phase difference of 180 degrees. The invention applies to a plant comprising free-piston air compressors or free-piston liquid pumps instead of auto-generators. The phase adjusting device may act on a factor other than the mass of air in the return energy pneumatic accumulators to control the frequency of reciprocation. Pressures occurring during the inward or outward strokes may be used to control the corresponding generator.