GB577740A - Improvements in or relating to the valve mechanism of internal-combustion engines - Google Patents

Abstract

577,740. Valve mechanism. SMITH, S. June 6, 1945, No. 14216. [Classes 7 (ii) and 7 (vi)] An internal combustion engine has an inlet valve 22 arranged concentrically within an exhaust valve 20 the latter having a tubular stem 19 sliding in a guide 17 which has a part-spherical seating 15 in the head to permit limited movement of the guide and thus allow correct seating of the exhaust valve. The cylinder head 9 has cooling water spaces 29 but the engine may be air-cooled or have the cylinder and head cast in one piece. The head has an exhaust valve seating 14 and a part-spherical portion extending to a flat top closed by a plate 40. The guide 17 has clearance in the bore 12 of the head and is prevented from rotation by a grub screw 4 which permits limited rocking movement of the guide. The cylinder-head has a pair of opposed exhaust ports 24 extending into separate exhaust manifolds 25. Two spark plugs extend horizontally from opposite sides of the cylinder head. Two interconnected channels 30 accommodate semicylindrical bars 33 which rest on ledges 34 and each bar carries four springs 32. The inner pair of springs on each bar have their ends engaging in one of a pair of grooves in the inlet valve stem while the outer pair engage in lugs 21 forming part of the exhaust valve. The two separate inlet valve springs on each bar may be replaced by a single double spring having a central U portion extending into a groove in the valve stem and retained by a cap fitting over the end of the valve stem. The plate 40 carries a casing 41 having bearings for an overhead cam-shaft 42 driven by a sprocket 43. A pair of cams 47 act through tappets 46 to control the exhaust valve while a cam 45 similarly operates the inlet valve through a recessed tappet 44. This valve may have a spherical seating in tappet 44. Preferably the cam centres are displaced from the tappet axes to cause rotation of the tappets during operation. The carburetters may be bolted directly to the top of the cam shaft casing so that the inlet gases have a vertical flow through casing 41 through the interior of the exhaust valve and the rotation of the cam shaft tends to produce turbulence in the mixture. In a modification, Fig. 4, the exhaust valve may be provided with grooves 50 having sharp upper edges and rounded lower edges to facilitate lubrication. Alternatively these grooves may be formed in the guide surface. In another modification, piston rings may be located in grooves in the guide surface. In some cases the inlet valve may move in a guide carried by a transverse rib in the exhaust valve.