Auxiliary section actuator air control system

A method for controlling a pressurized fluid operated shift actuator (220) for an auxiliary transmission section (14) of a compound transmission (10) including a main transmission section (12) having engaged and not engaged positions connected in series with said auxiliary transmission section, said auxiliary transmission section including a selectable high speed ratio and a selectable low speed ratio, each engageable by a synchronized jaw clutch assembly (92/128), switch means (98/98A/412) for selecting a desired auxiliary section ratio, said actuator (220) comprising a differential area piston (221) having a first piston surface (224) defining a first chamber (224A) and a second piston surface (222) defining a second chamber (222A), said first piston surface defining an area (a.sub.224) being larger than the area (a.sub.222) defined by said second piston surface, pressurization of said first chamber (224A) causing said actuator to urge said synchronized clutch assembly to engage said high speed ratio and pressurization of said second chamber (222A) causing said actuator to urge said synchronized clutch assembly to engage said low speed ratio, each of said chambers selectively connectable to a common source (234) of pressurized fluid and to an exhaust (EX), said method comprising:

• sensing the current engaged or not engaged position of said main transmission section;
• responding to sensing (i) a selection of a shift into auxiliary section high speed ratio and (ii) said main transmission section in not engaged position by pressurizing said first chamber and exhausting said second chamber;
• and
• thereafter responding to (i) continuing selection of a shift into auxiliary section high speed ratio and (ii) said main transmission section in engaged position by pressurizing both said first and said second chambers.

A system (300) for controlling a pressurized fluid operated shift actuator (220) for an auxiliary transmission section (14) of a compound transmission (10) including a main transmission section (12) having engaged and not engaged positions connected in series with said auxiliary transmission section, said auxiliary transmission section including a selectable high speed ratio and a selectable low speed ratio, each of said auxiliary section ratios engageable by a synchronized jaw clutch assembly (92/128), switch means (98/98A/412) for selecting a desired auxiliary section ratio, said actuator (220) comprising a differential area piston (221) having a first piston surface (224) defining a first chamber (224A) and a second piston surface (222) defining a second chamber (222A), said first piston surface defining a first piston surface area (a.sub.224) being larger than a second piston surface area (a.sub.222) defined by said second piston surface, pressurization of said first chamber (224A) causing said actuator to urge said synchronized clutch assembly to engage said high speed ratio and pressurization of said second chamber (222A) causing said actuator to urge said synchronized clutch assembly to engage said low speed ratio, each of said chambers selectively connectable to a common source (234) of pressurized fluid and to an exhaust (EX), said system comprising:

• means (204, 210, 332) for sensing the current engaged or not engaged position of said main transmission section, and
• means (246/326 and 328) for) pressurizing said second chamber whenever said main transmission section is in the engaged position thereof.

A system (230, 270, 300) for controlling a pressurized fluid operated shift actuator (220) for an auxiliary transmission section (14) of a compound transmission (10) including a main transmission section (12) having engaged and not engaged positions connected in series with said auxiliary transmission section, said auxiliary transmission section including a selectable high speed ratio and a selectable low speed ratio, each of said auxiliary section ratios engageable by a synchronized jaw clutch assembly (92/128), switch means (98/98A/412) for selecting a desired auxiliary section ratio, said actuator (220) comprising a differential area piston (221) having a first piston surface (224) defining a first chamber (224A) and a second piston surface (222) defining a second chamber (222A), said first piston surface of an area being larger than the area of said second piston surface, pressurization of said first chamber (224A) causing said actuator to urge said synchronized clutch assembly to engage said high speed ratio and pressurization of said second chamber (222A) causing said actuator to urge said synchronized clutch assembly to engage said low speed ratio, each of said chambers selectively connectable to a common source (234) of pressurized fluid and to an exhaust (EX), said system comprising:

• means (204, 210, 332) for sensing the current engaged or not engaged position of said main transmission section;
• means (324) for responding to sensing (i) a selection of a shift into auxiliary section high speed ratio and (ii) said main transmission section in not engaged position by pressurizing said first chamber and exhausting said second chamber;
• and
• means (328) for thereafter responding to (i) continuing selection of a shift into auxiliary section high speed ratio and (ii) said main transmission section in engaged position by pressurizing both said first and said second chambers.