Compound transmission and shift control therefor

A combined shift control assembly for a compound change speed drive train (10) comprising a manually shifted multiple speed main transmission section (12) connected in series with a two-speed range type auxiliary drive train unit (14), said control assembly comprising a shift bar housing assembly (56), a first axially movable shift rod (98) supported in said housing and having a first shift fork (52) fixed thereto for axially positioning a first main transmission section clutch (48) associated with main section drive ratios utilized in both of said auxiliary drive train unit range ratios, a second axially movable shift rod (96) supported in said housing and having a second shift fork (54) fixed thereto for axially positioning a second main transmission section clutch (50) associated for mainsection drive ratios utilized in only one of said auxiliary drive train unit range ratios, mainsection interlock means (108) for preventing axial displacement of more than one of said shift rods at a time from the axially nondisplaced positions thereof, said first shift rod carrying a first block member (130) defining a first pair of opposed strike surfaces (134,136) and said second shift rod carrying a second block member (122) defining a second pair of opposed strike surfaces (126,128), said control assembly characterized by:

• a control shaft (100) rotatably and slidably supported in said housing, said control shaft having selector means (118,120) fixed thereto for cooperation with said strike surfaces, said control shaft having a first rotational position (FIG. 6) wherein said selector means are engageable with said first pair of strike surfaces for selective axial displacement thereof, a distinct second rotational position (FIG. 7) rotationally adjacent said first rotational position wherein said selection means are engageable with said first pair of strike surfaces for selective axial displacement thereof and a third rotational position (FIG. 8) rotationally adjacent said second axial position wherein said selection means are engageable with said second pair of strike surfaces for selective axial displacement thereof, guide means located in said housing for limiting axial movement of said control shaft to said three rotational positions and for preventing rotational movement of said control shaft when said control shaft is in axially displaced condition, and switch means (150) internal of said housing activated by rotational movement of said control shaft inbetween the first and second positions thereof for causing the shifting of said auxiliary range drive train unit between the two range ratios thereof.