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;
• the rotational transmission assembly and the transmission shaft are coaxially disposed and an inner wall surface of one end of the rotational transmission assembly and an outer wall surface of the transmission shaft are axially and slidably connected, the other end of the rotational transmission assembly is connected with the drill bit;
• an annular space is formed between a middle portion of the rotational transmission assembly and the housing;
• the impact assembly comprises an impact ring located inside the annular space, and an outer wall surface of the impact ring and an inner wall surface of the housing are axially and slidably connected;
• one circle of first impact ratchets are uniformly disposed circumferentially on an end surface of the impact ring facing toward the drill bit;
• a plurality of impact springs are uniformly disposed circumferentially on an end surface of the impact ring away from the drill bit, and the other ends of the impact springs are connected with the housing;
• second impact ratchets cooperating with the first impact ratchets are disposed on an end surface of the rotational transmission assembly facing toward the impact ring;
• the end surface of the impact ring provided with the first impact ratchets is provided with a first impact portion;
• the end surface of the rotational transmission assembly provided with the second impact ratchets is provided with a second impact portion capable of cooperating with the first impact portion;
• during a process of rotation of the rotational transmission assembly along with the transmission shaft, when an end surface of the first impact portion of the impact ring and an end surface of the second impact portion of the rotational transmission assembly are mutually attached, ratchet tops of the first impact ratchets do not reach ratchet roots of the second impact ratchets and ratchet tops of the second impact ratchets do not reach ratchet roots of the first impact ratchets.