| 摘要 |
1491882 Adjustable IC engine valve gear YAMAHA HATSUDOKI KK 14 Oct 1974 [24 May 1974 26 June 1974 12 Aug 1974] 44379/74 Heading F1B A four-stroke I.C. engine comprising a camshaft 81, Fig. 3, for operating the or each inlet valve 21 and a cam-shaft 82 for operating the or each exhaust valve 22, has means for rotating one cam-shaft relative to the other in dependence on engine load so that when the throttle valve is substantially closed the degree of overlap for which both the inlet and exhaust valves are open is reduced as compared with the overlap during normal load operation of the engine. This enables the engine to be operated at low load with an air/ fuel mixture which is leaner than stoichiometric and thereby reduce the pollutants present in the exhaust gas. The cam-shafts are driven by a chain 85, and the means for rotating the cam-shafts relative to one another comprise a hydraulically actuable tensioner 90. In operation at low loads a valve 97 adlopts the position shown wherein the length 223 of the chain between the cam-shafts is a minimum representing minimum valve overlap. High-load operation as sensed by engine throttle linkage setting or inlet manifold pressure causes the valve 97 to switch to permit pressure fluid from source P to pass through line 97b into a cylinder 92 and force tension member 91 downwardly. Thus the length 223 of the chain increases between the cam-shafts causing relative rotation therebetween. In an exhaust gas recirculation system, the gas passes from a connection (44), Fig. 4 (not shown), through a pair of vacuumoperated valves (46, V) and individual pipes (13ad) to respective cylinder inlet conduits (12a-d), the valves (46, V) being operable in accordance with the degree of vacuum sensed in one of the inlet conduits. The pipes (13a-d) may be provided with non-return valves. |
