Expandable trailer with variable-pitch wheel carriage

An expandable trailer assembly comprising:

• (a) a trailer having a front end, an aft end, and a trailer deck structure, said trailer deck structure incorporating a first transverse component at a selected distance forward of the aft end of the trailer and a second transverse component aft of the first transverse component;
• (b) a trailer wheel carriage assembly comprising a left sub-carriage and a right sub-carriage, each carrying a forward axle and an aft axle in tandem, and each having a sub-carriage extension having a front end defining a sub-carriage extension tongue;
• (c) actuation means acting transversely between the right and left sub-carriages, for selectively moving the right and left sub-carriages either laterally outward away from each other or laterally inward toward each other;
• and
• (d) means for releasably fixing the longitudinal position of the right and left sub-carriages relative to the trailer deck structure;
• wherein:
• (e) the first transverse component defines laterally-elongate left and right tongue slots for respectively receiving the left and right sub-carriage extension tongues;
• (f) the second transverse component defines laterally-elongate left and right fulcrum slots for receiving respective intermediate regions of the left and right sub-carriage extensions;
• (g) the left and right tongue slots respectively define left and right upward-facing guide surfaces for respective engagement by downward-facing contact surfaces on the left and right sub-carriage extension tongues;
• and
• (h) the left and right fulcrum slots respectively define left and right upward-facing guide surfaces for respective engagement by downward-facing contact surfaces on intermediate regions of the sub-carriage extensions;
• wherein the guide surfaces of the tongue slots and the fulcrum slots are configured such that when the left and right sub-carriage extension tongues are respectively disposed within the left and right tongue slots, and the intermediate regions of the left and right sub-carriage extensions are respectively disposed within the left and right fulcrum slots:
• laterally-outward movement of the left and right sub-carriages will elevate the forward axles relative to the aft axles;
• and
• laterally-inward movement of the left and right sub-carriages will lower the forward axles relative to the aft axles.