Piston type air expansion shaft

The utility model discloses a piston type air expansion shaft which comprises a shaft sleeve and an inner shaft coaxially arranged in the shaft sleeve, pistons, air chambers and shaft heads are sequentially arranged at the two ends of the inner shaft outwards and wrapped by sealing rings to be arranged in the shaft sleeve, the pistons and the inner shaft can axially move in the shaft sleeve, and air nozzle assemblies capable of being connected with the outside are installed in the air chambers. The inner shaft is provided with a conical surface section in a circular truncated cone shape, an acute angle is formed between the outer conical surface of the conical surface section and the axis, a spring is arranged in a cross section open groove of the conical surface section, the two ends of the spring are fixedly connected with a pair of tensioning keys, and the tensioning keys are located in long grooves corresponding to the shaft sleeve and can move in the long grooves. The piston type air expansion shaft is e