Variable transmission assembly of heavy tractor

A variable-speed transmission assembly of a heavy tractor is composed of a mechanical reversing box, a five-shaft gearbox and a creeper gear box, the three box bodies are sequentially fastened into a whole through bolts in the front-middle-back direction, the mechanical reversing box comprises three front-stage gears and two rear-stage gears, the five-shaft gearbox comprises a four-gear main variable speed and a four-gear auxiliary variable speed which are spatially arranged in parallel, and the creeper gear box comprises a creeper gear and a creeper gear. The crawling gear box comprises a crawler, a transfer case and a PTO clutch, the mechanical reversing box can be interchanged with the power gear shifting box, and one of the mechanical reversing box and the power gear shifting box is selected. The power gear shifting box is of a three-shaft type, the three shafts are arranged in a triangular shape, and power reversing and power high-low gears are achieved. Three independent modules are combined, multifunct