A heavy-duty active suspension, including a suspension frame, a lifting unit, a pin axle, a through axle, two wheel-driving units, an encoder, and a displacement sensor. The lifting unit is mounted on an upper side of the suspension frame for driving a heavy-duty support platform to rise and descend. The pin axle is mounted across the suspension frame along a front-rear direction. The through axle is rotatably mounted on the pin axle through a bearing, and is across the suspension frame along a left-right direction. The two wheel-driving units are respectively mounted on both ends of the through axle. The encoder is installed on the through axle for measuring a swing angle of the through axle. The displacement sensor is installed between an output end of the lifting unit and the suspension frame. A suspension vehicle including the active suspension and a leveling control method thereof are further provided.

A tractor unit for transporting an elongated load includes a body that is supported, driven and steered by a wheel set comprising at least three ground-engaging wheels. At least two of the wheels are steerable and can transform between an aligned mode and a carousel mode. In aligned mode, the wheels are steerable and aligned with one another in a neutral steering position. In carousel mode, the wheels are oriented with their axes of rotation intersecting at a substantially common vertical axis within the the tractor unit body, so when the wheels are driven the tractor unit spins about this vertical axis. A load engagement mechanism is mounted pivotally on the tractor unit body about the vertical axis to allow counter rotation in an equal and opposite amount to the rotation of the tractor unit body in carousel mode, keeping the load fixed relative to the ground as the tractor unit spins.