Variable-cylinder-diameter brake master cylinder of electric three-wheel passenger car

The invention provides a variable-cylinder-diameter brake master pump of an electric three-wheeled passenger car, which comprises a master pump cylinder body, a piston, a return spring for applying acting force to the piston and an oil can, a small-diameter cylinder body front cavity, a large-diameter cylinder body rear cavity, a cylinder body oil outlet, a cylinder body front cavity oil port and a cylinder body rear cavity oil port are arranged in the master pump cylinder body, the cylinder body oil outlet is arranged at the cylinder body front cavity, and the cylinder body rear cavity oil port is arranged at the cylinder body rear cavity oil port. The cylinder body front cavity oil port and the cylinder body rear cavity oil port are communicated with each other and are respectively communicated with the corresponding cylinder body front cavity and the corresponding cylinder body rear cavity; the piston comprises a piston body, a cylinder body front cavity piston matched with the cylinder body front cavity a