Single-stage suspension system for bogie of low-floor tramcar

The invention discloses a primary suspension system for a bogie of a low-floor tramcar. The primary suspension system comprises a wheel pair, a framework and an axle box device, the axle box devices are arranged on axles of the wheel pairs and located on the inner sides of the wheels, and the two axle box devices on each wheel pair are symmetrically arranged along the longitudinal axis of the framework. An axle box body of the axle box device is provided with a first connecting end rotationally connected with an axle, a second connecting end arranged above the framework, and a connecting middle section; a primary suspension is formed between the second connecting end and the upper surface of the framework; one side of the axle box body is arranged in the wheel in an intrusive mode, and the other side of the axle box body obliquely extends from the first connecting end to the second connecting end, so that two opposite axle box devices on the axle are located on the longitudinal axis side of the framework to f