Excitation device for automatic injection pen

The utility model relates to an excitation device for an automatic injection pen. The excitation device comprises a shell, a needle hiding sleeve, an inner sleeve and a piston assembly, the hidden needle sleeve is installed in the shell in a sliding mode. A lower spring sleeve is fixed on the inner side of the lower part of the needle hiding sleeve; a lower spring clamping hook protruding inwards is arranged on the upper portion of the lower spring sleeve. The inner sleeve is mounted in the needle hiding sleeve in a sliding manner; a sliding groove is formed in the outer side of the lower portion of the inner sleeve, and the lower spring clamping hook is clamped in the sliding groove. A narrowing spring is arranged between the lower part of the inner sleeve and the lower spring sleeve; a medicine pushing spring is arranged on the outer side of a spring supporting part of the piston assembly and is pressed against the top of the inner side of the inner sleeve in a pre-compression mode. According to the automat