Calibration system for a power shift transmission

In an agricultural vehicle comprising an engine, a governor coupled to the engine to regulate a fuel flow rate of the engine, a transmission coupled to the engine to couple power from the engine to the ground at a plurality of different gear ratios, the transmission having a drive train including a plurality of gears arranged on a plurality of shafts such that selective engagement of the gears allows the transmission to be engaged in a plurality of gear ratios, the drive train further including a plurality of fluid clutches arranged in the transmission to fix the gears to the shafts in the plurality of gear ratios, at least a first and second of the clutches being disposed to couple at least four of the gears with respect to at least two of the shafts to simultaneously engage the two shafts in two incompatible gear ratios, and a third of the clutches having an input and an output and disposed in drive train between the two clutches and the engine such that the third clutch can selectively engage the engine to at least one of the two shafts, the vehicle further including a plurality of fluid valves coupled to the plurality of clutches, a method for calibrating the third clutch, comprising the steps of:

• engaging the first and second clutches to fix the at least two shafts in a plurality of incompatible gear ratios;
• sensing a first value indicative of a reference engine load;
• after the step of sensing a first value, incrementing a fluid pressure applied to the third clutch;
• after the step of incrementing, sensing a second value indicative of a current engine load;
• after the step of sensing a second value, comparing the first value and the second value to determine whether the current engine load exceeds the reference engine load by a predetermined amount, and
• repeating the incrementing, sensing a second value and comparing steps until the comparing step indicates that the current engine load exceeds the reference engine load by the predetermined amount.