| 摘要 |
<p>654,239. Steam engines; valve gear. ALESSIO, G. Aug. 23, 1946, No. 25202. Convention date, July 21, 1944. [Classes 122(ii) and 122(iii)] In a simple expansion, double acting, multi-cylinder steam engine having a valve gear controlled by independently variable rotary cams which provide for regular operation of the engine with a low cutoff, starting of the engine with a high cutoff, stopping of the engine by setting the reverse control at its mid position, and coupling of the engine with an exhaust steam turbine operating only during forward running with the compression period of the engine in forward gear adjusted so as to provide a final compression which is nearly constant under varying loads, and in reverse gear to have the engine operating only in uniflow, means are provided for correcting the effect exerted by the obliquity of the connecting rods on the cut-off. The engine has cylinders of the uniflow type having auxiliary exhaust valves, and a condenser, said auxiliary valves being controlled by combined action rotating cams so adjusted as in forward gear, to ensure an exhaust period increased proportionately to an increase in load so as to obtain a substantially constant ratio of compression to exhaust pressure and turbine feed pressure, and in reverse gear, to ensure that a maximum compression is obtained, the exhaust of the engine in this latter case being directly to the condenser. The poppet valve system employed is operated and controlled as described in Specifications 654,240 and 654,241. The obliquity of the connecting rod is compensated by adjusting the cut-off by means of apparatus comprising a pair of beams B mounted oppositely to each other on either side of the opening cams A1 and the closing cams A2 for each valve V1 and rollers R1, R2 provided at either end of the beams, which rollers bear on the opening and closing actuating cams for the valves, and are so arranged that the distance d1 between the rollers is different from that. d, between each pair of cams A1, A2, so that the rollers which bear on the closing cams of each pair, in forward gear, move in advance or delay with respect to those bearing on the opening cams.</p> |
