Vehicle, power system, braking system and braking method

The invention discloses a vehicle, a power system, a braking system and a braking method. The brake system comprises a relay valve, an electric control unit and a gas circuit control part, the relay valve further comprises an air hole e, an air hole f and an air chamber F besides parts such as a valve element, a valve rod, four air holes a-d, five air chambers A-E, an air cylinder and a vehicle brake air chamber. The air hole f is connected with the air chamber F, the air hole e is connected with the air storage cylinder through the air hole d, and the air path control part is provided with an air port I connected with the air hole f, an air port II connected with the air hole e and an air port III for exhausting air outwards. The electric control unit can automatically control the on-off state of the air port I, the air port II and the air port III according to a preset electric signal, so that the flowing direction of compressed air inside and outside the relay valve is adjusted, and the braking force on wh