Wheel frame assembly for quick expansion and folding

A wheel frame assembly capable of being folded and expanded, comprising:

• a retainer frame having two parallel retaining rods and at least one transversal rod to be between the two retaining rods so that the two retaining rods are firmly secured in a parallel relation;
• and each retaining rod being engaged with a bush;
• each bush having at least one axial hole;
• at least two rotary units;
• each rotary unit being formed by assembling a sleeve with a wheel;
• an inner wall of the sleeve being formed with a slightly cambered guide trench;
• a front end of the guide trench being higher than a rear end thereof;
• each sleeve of the rotary units being engaged to a corresponding one of front ends and rear ends of the two retaining rods so that the sleeves can drive the wheels to rotate along the two retaining rods;
• an active frame has two parallel active rods;
• at least one transversal bar for positioning the active rods;
• each active rod being penetrated by a guide shaft and a positioning block;
• the guide shaft penetrating through a bottom of the active rod;
• each positioning block having a stud;
• each active rod passing through an axial hole of the bush so that the active frame is fixed at an upper side of the retainer frame and each guide shaft being penetrated into the guide trench of the rotary unit;
• a pin assembly installed to the retaining rod of the retainer frame;
• the pin assembly including a rod unit which is engaged to the rotary unit;
• the pin assembly having a wire for controlling the rod unit to separate from the rotary unit;
• the wire being connected to a switch on a linkage;
• when the switch is turned on, the wire is tightened, the rod unit will separate from the rotary unit.