Bottom-hole impact-rotation stepping combined unloading rock-breaking efficient drilling system and method thereof

A bottom-hole impact-rotation stepping combined unloading rock-breaking efficient drilling system, comprising:

• a cylindrically-structured housing;
• wherein a drive assembly, a universal joint, a transmission shaft and a rotational impact assembly sequentially connected along an axial direction are disposed in the housing;
• an end of the rotational impact assembly is provided with a drill bit;
• an outer wall surface of the transmission shaft and an inner wall surface of the housing are rotatably connected;
• the rotational impact assembly comprises a rotational transmission assembly for conveying a rotational power to the drill bit and an impact assembly for providing a high frequency axial impact power to the drill bit;
• an end of the rotational transmission assembly is connected with the transmission shaft and the other end is connected with the drill bit;
• when the rotational transmission assembly rotates along with the transmission shaft, the impact assembly applies a high frequency impact force along a drilling axial direction to the rotational transmission assembly;
• an annular drill bit is disposed at an outer end of a drill bit body of the drill bit;
• a central drill bit is slidably disposed on an inner ring end surface of the annular drill bit;
• a drill bit inner cavity is disposed inside the drill bit, and a force applying assembly for axially pressing out the central drill bit outwardly is disposed inside the drill bit inner cavity;
• an inwardly-recessed cylindrical region is formed between a head end of the annular drill bit and a head end of the central drill bit.