| 摘要 |
A valve mechanism includes a valve (11) having a valve stem (14) which is located for axial movement in a valve guide (13) and valve head (15) adapted at one extreme of movement of the valve (11) to locate against and close a valve seat (16); a valve lever (20) is pivotally mounted at one end (21) and is attached adjacent the other end (23) to the end (22) of the valve stem (14), the valve lever (20) defines a track (25); a drive pin (32) engages in the track (25) the drive pin (32) being mounted at one end of a first link (30) the other end of the link (30) being pivotally mounted about a fixed pivot (31), a second link (40) is pivotally mounted at one end about moveable pivot (41), the first and second links (30,40) being interconnected by an intermediate link (45) pivotally attached to said first and second links (30,40) at positions separated from their pivots (31, 41) a drive link (52) is pivotally connected at one end to the pivotal connection between the second link (40) and intermediate link (45) and at the other end to a crank (51), so that rotation of the crank (51) will cause the linkage (30,40,45) to oscillate and the drive pin (32) to perform a reciprocating motion along an arucate path defined by first link (30); the track (25) has a first portion (26) which is engaged by the drive pin (32) when the valve (11) is olosed and coincides with the arcuate path of the drive pin (32) and a second portion (27) which diverges from the path of the drive pin (32), so that engagement of the second portion (27) by the drive pin (32) will cause the valve lever (20) to move opening and closing the valve (11); and means (55) being provided for movement of the pivot (41) to vary the timing and duration of opening of the valve (11). |
