GB800395A - Improvements in or relating to percussive tools operated by a direct-acting internal combustion engine - Google Patents

Abstract

800,395. Direct-acting two-stroke engines; carburetting-apparatus; starting; igniting; valves and valve-gear. KNORR-BREMSE G.M.b.H. Aug. 9, 1956 [May 19, 1956 (3)], No. 24481/56. Classes 7(2), 7(3). 7(4), 7(5) and 7(6) [Also in Groups XXIII and XXVI] To compress combustible mixture admitted to a combustion chamber 8 by a valve 11, the piston 2 of a percussive tool is moved by compressed air admitted to its under surface via a conduit 22 under the control of a slide valve 12 so actuated in dependence on combustion chamber pressure that it is on a seating 13 during mixture'ignition. The valve 12 then connects the conduit 22 to a duct 23 so that on its power stroke the piston 2 drives the air through cylinder wall cooling bores 24, finally both striking an anvil 4 non-positively linked to a chisel 5 and uncovering terminal exhaust ducts 43, the lowered combustion chamber pressure allowing (a) the valve 11 to open under mixture supply pressure to an extent determined by a ledge either engaging the valve head or the abutment disc 15 of an auxiliary valve-closing spring and (b) the valve 12, under air pressure in a chamber 40, to enter the chamber 8 to an extent determined by a ledge 42 engaging the valve head or by a ledge engaging a disc corresponding in position to the disc 15. The valve 12 then connects the conduit 22 to a compressed air supply duct 21, so that the piston moves on its compression stroke, and the combustion chamber pressure, having caused closure of the valve 11, seats the valve 12 at the moment when the consequent pressure reduction in the conduit 22, delayed if necessary by the narrowness of the duct 23, will allow a piston 26 previously held up by the air pressure to open an ignition make-andbreak 28 under the action of a leaf spring 27 and operate a spark plug 10 with correct timing. The valve 11 is supplied from a mixing chamber 35 supplied with air from the duct 21 which also via a ball valve 29 pressurizes a tank 30 and forces fuel up a duct 32 to a mixing chamber nozzle 33. Partial release of an operating handle 44 allows closure of a ball valve 31 and the tool operates on compressed air alone at reduced speed. Complete release of the handle 44 stops tool operation by closing the entry 48 from the duct 21, a duct 45 being opened to continue a supply of air to the cooling bores 24. At all times, cylinder-head cooling bores 47 are supplied from the duct 21 via a narrow bore 46.