Patent GB-646987-A (GB)
Title: Improvements in or relating to percussion devices, particularly for ramming and tamping, operated by direct acting internal combustion engines
IPC: E02D3/061
Filed: 1947-08-06
Abstract: 646,987. Direct-acting engines; spray carburetters; non-compression engines; valves. BARD, F. N. Aug. 6, 1947, No. 21366. Convention date, June 7. [Classes 7(ii), 7 (iii) and 7(vi)] An internal-combustion operated percussive device, particularly for ramming and tamping comprises a body portion having a cylinder 19 therein, a piston 24 movable in the cylinder, means for delivering a combustible charge to the cylinder and igniting the charge to move the piston in one direction, a spring 28 for moving the piston in the other direction an auxiliary exhaust opening 31 in the cylinder so located as to remain uncovered by the piston during at least the major portion of its return movement effected by the spring but to be covered by the piston by the end of its return movement, a valve member 33 for closing the opening valve member being so located that pressure admitted to the exhaust opening from the cylinder tends to move it to closed position and a spring 34 normally urging the valve member to open position the spring being strong enough to keep the valve member open during return movement of the piston, but allowing the valve to close during each working stroke under pressure of gases in the cylinder. The piston is shown at the top of its stroke. As it moves downwardly it first uncovers the port 31 and then when it has moved sufficiently uncovers exhaust ports 27a, 27b. The burned gases in the cylinder escape through the ports and the piston is returned by the spring 28. During the return movement however the pressure of the gases which remain in the cylinder is insufficient to hold the valve 33 closed and these gases can escape through the port 31. The rammer is controlled by a handle 12 which operates a piston 18. The piston 18 is first moved downwardly any remaining gases in the cylinder passing out through an opening 18a in the piston, a valve 17 being opened during this movement and the piston 18 is then raised again drawing in a fresh charge through a carburetter 20. During the upward movement of the piston a magneto (not shown) is operated by an operating lug carried by an extension of the piston rod 16. The magneto is then rotated by a spring to produce a spark at a sparking plug 23. Fig. 5 is a section on the line 5-5 of Fig. 4. Petrol from a tank 44 passes through a filter (not shown) and a pipe 43 to a needle valve 42 controlling an orifice 41a. When the piston 18 moves upwardly it opens valves 48 and 40 and air is drawn in through a pipe 46 and mixed with fuel from the orifice 41a. During a working stroke the valve 48 closes and protects the valve 40 from the products of combustion. The pipe 46 terminates at a filter (not shown) located beneath the fuel tank. Provision is made for circulation of the air beneath the fuel tank 44 and this is improved by the intake of air through the pipe 46a. The body portion of the rammer is in three parts A, B, C held together by bolts (not shown). The strength of the spring 34 is such as to hold the valve 33 closed against a pressure of between 5 and 20 pounds per square inch. In one very satisfactory arrangement the valve 33 would just open against a pressure of 7 pounds per square inch. Preferably the valve 48 is at least 50-75 per cent greater in area than the lower valve and the spring load of the upper valve is slightly greater than that of the lower valve proportionately to its area. The loading of the valves is preferably such that it takes a slightly greater depression to lift the valve 48 from its seat so that the instant this valve lifts the carburetter valve 40 immediately lifts. The valve 48 closes if anything slightly ahead of the valve 40. Specification 672,998 is referred to.