Electronic control auxiliary braking system of relay valve

The invention discloses an electronic control auxiliary braking system of a relay valve, which comprises an upper cover, a middle shell and a lower body which are sequentially connected from top to bottom; through holes which communicate with one another are formed in the upper cover, the middle shell and the lower body; a cavity is formed in the upper cover, the middle shell and the lower body; a linkage rod and a piston are arranged in the cavity from top to bottom, and a valve and an inner cover are arranged in the piston; the valve and the inner cover can move relative to each other and a middle spring is arranged outside the valve and the inner cover, the upper end and the lower end of the middle spring abut against the lower end of the valve and the lower end of the inner cover respectively, a lower cover is arranged on the lower portion of the lower body, a lower spring is arranged in the lower cover, and the upper end and the lower end of the lower spring abut against the lower end of the inner cover