Patent GB-736585-A (GB)
Title: Improvements in or relating to opposed piston two-stroke internal combustion engines
IPC: F02B75/02
Filed: 1951-02-26
Abstract: 736,585. Two-stroke cycle opposed-piston engines; reversing valves. DOXFORD & SONS, Ltd., W., PURDIE, W. H., and JACKSON, P. Feb. 22, 1952 [Feb. 26, 1951], No. 4685/51. Classes 7(2), 7(5) and 7(6). [Also in Group XXIX] In a reversing opposed piston twostroke cycle engine in which the pistons 1, 5 are operatively connected to separate cranks 2, 6, 7 on a crank shaft and in which air for scavenging and combustion is admitted to the cylinder through ports in the cylinder wall at or near one end thereof (usually the end nearer the crank shaft) and exhaust takes place through ports 15 in the cylinder wall at or pear the other end thereof, the crank operating the exhaust controlling piston leads by 4 to 8 degrees the crank operating the air controlling piston, and there are two sets of air ports of which one set without valve means is nearer to the adjacent end of the cylinder than the other and is exposed by the air controlling piston after the other, the set which is exposed first being provided with valve means operable to close the ports against return flow until the pressure in the cylinder has fallen to the air supply pressure and this set remaining exposed substantially until or after the exhaust ports have been closed. As shown there are two rows of inlet ports 10, 13 and non-return valves, not shown, are associated with the ports 10. An air chamber 14 is provided. The supercharging air may be supplied by the means described in Specifications 711,904 or 736,581 or by an extra large reciprocating blower or blowers or by Roots, vane or centrifugal blowers. The exhaust ports open first and then the ports 10 are uncovered but they are not opened by the non- return valves until the cylinder pressure is less than that in the chamber 14. Finally the ports 13 are opened. The exhaust ports are closed before the ports 10 so that air for supercharging can flow in through the latter ports. In a modification the non-return valves are replaced by an oscillating rotary sleeve valve operated by a cam driven by the engine cam shaft. Two cams are provided for reversing, one for each direction of rotation. The sleeve valve does not close until the ports are covered by the piston on the up stroke. In this embodiment the exhaust crank leads by up to 6 degrees. The sleeve valve may be timed to open the air ports about 25 degrees before the end of the outward stroke. The loss of air may be restricted by the early closing of the exhaust ports and the exhaust ports may stop short of the end of the piston stroke to further reduce the loss of air. The non-return valve may be of the multi-disc type or a flap valve or valves. Fig. 5 shows the construction of the non-return valve used in Fig. 1. Plate valves 43 co-operate with trough shaped members 45. The plate valves are held against the trough shaped members to prevent the flow of air when the pressure in the cylinder is higher than in the air chamber. The sleeve may be oscillated, rotated and/or reciprocated. The exhaust ports may be fully exposed when the valve controlled ports are fully exposed or when the uncontrolled ports are just opening. In cases where it is desirable that a proportion of cool air be mixed with the exhaust gases, for example, when an exhaust driven turbo blower is used for supercharging the exhaust ports preferably extend to the end of the stroke.