A vehicle transmission having gear ratios in a main gearbox overlapping gear ratios in an auxiliary gearbox

摘要

A vehicle transmission comprises a main gearbox G and an auxiliary planetary gearbox P having two planetary gear trains 12, 13; the group ratios in the main gearbox G being such that they overlap between the adjacent group ratios in the gearbox P, so that by selecting a ratio in gearbox G the required operating speed is obtained by selecting the mid-ratios (B, C fig 4) in gearbox P. The gear trains 12, 13 ratios are selected by valve control means (50a - 55, fig 4) which operates fluid powered clutches C1 and C2 that are paired with bellville spring operated clutches C3 and C4 respectively. Engagement/disengagement of the clutches is sequenced by matching fluid flow and free play in the clutches. The control means (50a - 55, fig 4) comprises cam means, or a microprocessor, moved by ratio selector means which operates switches for energising the solenoid valves that operate the fluid clutches. An additional planetary gear train (100, fig 9) may be provided. IMAGE