英语翻译
From section BB it can be seen that a mechanism comprising an eccentric
in a scotch yoke slides vertically in the two-piece casting that forms not only
the housing but also the driveshaft bearings and caps.Rotation of the control
shaft moves the whole assembly laterally,and therefore the driveshaft into
and out of concentricity with the camshaft sections.The control shaft can be
rotated through only 90° which is why,when it has been actuated to bring the
driveshaft into its eccentric position,as in section BB,there is no clearance
above the scotch yoke.
By arranging the belt or chain drive as in Fig.3.26,lateral movement of
the driveshaft can be made to cause also a phase change.The resultant
changes of the valve timing are illustrated in Fig.3.34,which shows what
the lift characteristics are with the standard timing,what they would be if
only event timing were changed and what it is when both event timing and
phase shift are applied.The whole system can be applied to both the inlet
and exhaust valves but,for optimum cost-effectiveness,only the inlet valve
timing would be varied.
The operating envelope is of course limited by the stresses superimposed
on the valve train by the accelerations due to advancing and retarding the
timing.However,if the eccentricity of the drive is introduced only at speeds
of 2000 rev/min and below,the total stresses in the valve train need be no
higher than those with fixed valve timing at 4000 rev/min.Tests with twin
cylinder motorcycles have shown 32% increases in power and 43% reductions
in specific fuel consumption.