Patent GB-760161-A (GB)
Title: Improvements in free piston internal combustion power hammer and percussion tools
IPC: E02D7/10
Filed: 1954-05-31
Abstract: 760,161. Diesel-acting engines ; starting. McKIERNAN-TERRY CORPORATION. May 31, 1954 [June 18, 1953], No. 16093/54. Classes 7 (2), 7 (3), 7 (5) and 7 (6). A power hammer or percussion tool comprises a ram 10, Fig. 1, connected to a piston 11 above which is formed an air compressing and cushioning chamber 14 and below which is formed an annular combustion chamber 15 into which is injected at the end of the down stroke compressed air through a passage 22 and fuel through nozzles 37, the piston cylinder being provided with a main exhaust port 40 which opens at the end of the upstroke and an auxiliary exhaust port 41 which allows escape of gases from beneath the piston on the downstroke to permit the ram to strike a substantially uncushioned blow. On the upstroke the piston 11 compresses air through a valve 18 into a reservoir 19 provided with a valve 20 which is opened by a rocker 26 actuated by a cam 32 on the ram 10 at the end of the downstroke of the piston to admit compressed air through passages 21, 22, containing a non-return valve 23, to the combustion chamber 15, fuel being simultaneously injected through the nozzles 37 by pumps 33 actuated by a cam 34 on the piston rod 35 which rod also carries a cam 39 controlling firing of the sparking plug 38. The auxiliary exhaust port 41 is connected by a pipe 46 to a valve seat 45, Fig. 2, closed by a ball valve 44 actuated by a differential piston 52 having its lower, larger area side connected by a pipe 48 to the compressed air injection passage 21 and its upper, smaller area side connected by a pipe 50 to the reservoir 19. When the valve 20 opens at the end of the downstroke the pressure of the compressed air in passage 21 forces the piston 52 upwards to close valve 44, which valve remains closed throughout the upstroke as the combustion chamber pressure holds the non-return valve 23 on its seat and prevents release of pressure from the passage 21. When the main exhaust port 40 opens, the drop in pressure in the cylinder permits valve 23 to open and the piston 52 is forced downwards to open the valve 44 and allow the gases beneath the piston 11 to escape through the auxiliary port 41, permitting the piston 11 to drop freely until the port 41 is overrun by the piston 11 almost at the end of its downstroke. The piston 11 is cushioned at the end of the upstroke by air trapped in the space 14. The device is started by lifting the piston 11 by compressed air supplied to the reservoir 19 through a valve 54. In a modification, Figs. 4 and 7, the piston 11 is provided with an extension 55 which acts as an air compressor forcing air into a coaxial reservoir 61 which is connected by a pipe 62 to the air injector valve 20. The opening and closing of the auxiliary exhaust passage 78 is controlled by a poppet valve 75, Fig. 7, actuated by a cam 73 on a differential piston 67 connected by passages 69, 71 to the compressed air reservoir 61 and combustion chamber 15 respectively.. The anvil block 83 is loosely coupled to the lower end of the cylinder by links of cable 84 and the valve 20, the fuel injection pumps and the ignition device are all actuated by a cam 32 on the end of the ram 10.