Auxiliary transmission section shift control system

A control system for a splitter type change gear auxiliary transmission section of a compound vehicular transmission comprising a main transmission section connected in series with said auxiliary transmission section and drivingly connected to a fuel controlled engine by a selectively engaged and disengaged master friction clutch, said auxiliary section having at least three engagable auxiliary speeds, said control system of the type permitting preselection of a auxiliary section gear change to be executed upon achievement of enabling transmission operating conditions, said control system comprising;

• an operator actuated gear selector valve having a selector switch movable to at least three positions to preselect a desire engaged auxiliary transmission section gear, said selector valve connected to a source of pressurized fluid, a first selectively pressurized and exhausted fluid conduit, a second selectively pressurized and exhausted fluid conduit and an exhaust conduit, in said first position of said selector switch said selector valve establishing communication between said source and said first selectively pressurized and exhausted conduit and exhausting said second selectively pressurized and exhausted conduit, in said second position of said selector switch said selector valve exhausting both of said first and second selectively pressurized and exhausted conduits and blocking said source, and in said third position of said selector switch said selector valve connecting said second selectively pressured and exhausted conduit to said source of pressurized fluid and exhausting said first selectively pressurized and exhausted conduit;
• an actuator valve assembly remote from said gear selector valve and having a supply port in constant fluid communication with said source of pressurized fluid, a first pressure line port and a second pressure line port, said actuator valve assembly including piston means having a first position of engagement of a first selected gear, a second position for engagement of a second selected gear and a third position for engagement of a third selected gear, said piston means assuming said first position from one of said other positions only upon the occurrence of said enabling conditions and pressurization of said first pressure line port and exhaust of said second pressure line port, said piston means assuming said second position from one of said other positions only upon the occurrence of said enabling conditions and exhaust of both said first and second pressure line ports and said piston means assuming said third position form one of said other positions only upon the occurrence of said enabling conditions and pressurization of said second pressure line port and exhaust of said first pressure line port;
• said control system characterized in that:
• said first selectively pressurized and exhausted conduit connecting said selector valve directly to said first pressure line port and said second selectively pressurized and exhausted conduit connecting said selector valve directly to said second pressure line port;
• said actuator valve assembly comprises a valve body defining a first enlarged cavity adjacent said supply port, a second enlarged cavity adjacent said first pressure line port and a third enlarged cavity adjacent said second line port, said fluid cavities in fluid communication with working surfaces of said piston means;
• the force of said pressurized fluid acting on the working surfaces of said piston means being insufficient to cause said piston means to assume a different position when said engine is fueled substantially above idle speed and said master clutch is engaged;
• and
• said enabling conditions occur upon either disengagement of said master clutch and/or a significant reduction of fuel supply to said engine.