GB580536A - Improvements in or relating to the starting of internal-combustion-operated free-piston machines - Google Patents

Abstract

580,536. Free-piston gas generators. MUNTZ & CO., Ltd., A., and BEALE, E. S. L. Sept. 8, 1943, No. 14747. [Class 7 (i)] An internal-combustion operated air-compressor or gas-generator of the free piston type par- 'ticularly a generator forming one unit of a plant comprising several units delivering to a common manifold has a starting control member which is actuated to initiate a predetermined sequence of starting operations said sequence being automatically repeated until starting occurs and being then automatically stopped. The starting mechanism may be used in conjunction with the control system described in Specification 580,532, which includes a master control gear arranged to actuate in unison the main control levers 67, Fig. 1; of individual generators thereby determining the output and controlling the starting and stopping of individual generators. Each generator comprises opposed free pistons 16 and is supplied with scavenging air from the casing 13 and delivers from ports 17 to a collector 18 connected by a valve 117 to the common manifold. The collector has a blow-off valve 20 controlled by a pressure-responsive device 22 and oil pressure relay. Starting-air chambers 23 are connected to cushion chambers 15 by a port controlled by a valve 24 on a piston 26. The pistons are manoeuvred,to their starting position by a pneumatic servo-motor 28 controlled jointly by a manoeuvring air valve MAV and starting air valve SAV. The control system also includes a repeater valve RV having two plungers both biased downwardly by springs. The upper one is raised by engine case pressure applied to a valve 41. In either upper or lower position the port 43 to which starting oil pressure SOP is applied, oil passes along line 123 to starting- control valve CV which is supplied with oil at a variable pressure COP determined by the master controller. The valve is also connected to a source of constant pressure (relay oil pressure ROP). The manoeuvring servo-valve MSV has a plunger coacting with the piston 65 connected to the main control lever 67 of the individual generator which is biassed to stop position by a spring 66. In operation, when the gas generator is brought to rest the pressure SOP falls to atmospheric and plunger of valve CV moves to the left closing port 58. This cuts off line 120 and unloads pressure device 22 so that valve 20 is opened and collector 18 exhausts to atmosphere. Bye-pass valve 118 also opens and exhausts the engine casing 13. Port 63 of valve CV is also open to drain port 56 and a plunger 74 of valve SAV drops. Relay oil pressure from line ROP moves piston 65 to the left and lever 67 to its stop position.. Movement of plunger 68 of valve MSV by piston 65 applies pressure ROP through line 103 to raise the piston 97 of valve MAV thus lifting the valve 107, 108. This causes the air supply to open a cushion release valve 33 and supplies air to the manoeuvring cylinder 28 to set the pistons in starting position. At the end of the stroke of rod 30 air is released to a line 105 to operate a trip finger 101 and allow valve 108 to drop. Valve 33 is also closed by its spring. The pistons being thus in starting position the starting operation is initiated by the master control which applies starting oil SOP at port 43 and through line 123 to move valve CV to the right (as shown). Control oil pressure is now effective through port 61 first to close blow-off valve 20 and then to move control lever 67 to a running position depending on the magnitude of control oil pressure. The relay oil pressure is cut off at port 71 and line 103 and piston 97 of valve MAV drops. The same pressure is applied to line 78 to raise a piston 76 of valve SAV as far as is allowed by a catch 79 and slightly opens valve 88. The air so released will if the manoeuvring gear rod 30 is retracted pass through the open valve 31 and cause release of catch 79. Piston 76 then rises as far as a second catch 80 and opens valve 88 fully. Air can thus pass along line 93 to starting air chambers 23 via valves 27. Air in line 94 also raises valve 35 which picks up the upper plunger and raises it to the position shown, the pressure SCP still passing to valve CV. When the pressure in air chambers 23 has reached a suitable value it causes release of catch 80 and further lift of piston 76 whereupon the finger 84 is cammed aside and valve 88 shuts. Pressure in line 93 is released thus causing starting valves 24 to open and drive the free pistons towards each other. If the generator starts engine case pressure maintains the valve plunger 36 in raised position, maintaining the illustrated position of valve CV. The lower plunger 35 is returned by its spring. If the generator fails to start the upper plunger 36 slowly falls and cuts off pressure SOP from valve CV which moves to the left in readiness for another attempt at starting. This next attempt automatically repeats the above described sequence of operations and is initiated when valve 36 has fallen to its lowest position wherein the supply port 45 reopens communication with line 123. Specification 540,855 also is referred to.