Upper-part rotation speed-limiting device for rotary drilling rig

The utility model relates to a speed-limiting system adopting negative flow to control rotation of the upper part of the rotary drilling rig, which aims at providing a speed-limiting system capable of improving comfort of operation, quickly and precisely limiting rotation speed of the upper part and eliminating influence of load variation on rotation speed. The upper-part rotation speed-limiting device includes a hydraulically-controlled guiding handle, a negative flow piston pump, a negative flow multi-passage valve and a rotation motor. A negative feedback port FI of the negative flow multi-passage valve is communicated with a negative control port PI of the negative flow piston pump through a negative control feedback oil path. A hydraulic part which is capable of choosing is arranged on the negative control feedback oil path, and the hydraulic part comprises at least two oil inlet ports P3 and P4 and a work oil port A3. The inlet oil port P3 is communicated with the negative feedback port of the negative flow multi-passage valve FI, the work oil port A3 is communicated with the negative control port PI of the negative flow piston pump, P4 is communicated with a hydraulic source supplying a stable pressure Pi, and the work oil port A3 is communicated with an oil inlet port with a larger pressure chosen from the two oil inlet ports P3 and P4.