Force-limiting device for an aircraft landing gear shock absorber, and a shock absorber including such a device

A shock absorber for the landing gear of an aircraft, in particular of a helicopter, the shock absorber comprising a main body in which a rod-piston slides, including both a diaphragm hydraulic shock absorbing means that acts under normal conditions of use, and a two-chamber energy-absorbing means comprising one chamber containing gas at low pressure and another chamber containing gas at high pressure, which means acts during a crash landing, the shock absorber including a force-limiting device which comprises:

• a box fixed in the main body to form a partition for said main body, the bottom of said box co-operating with the end face of the rod-piston to delimit a hydraulic fluid chamber, and also being surmounted by a volume of hydraulic fluid which is adjacent to the low pressure chamber, said low pressure chamber also being delimited by a separator piston which also serves to delimit the adjacent high pressure chamber, said bottom further including a plurality of small throttling orifices;
• an annular valve member disposed around the diaphragm and enabling a large volume of hydraulic fluid to pass therethrough in a very short time when it is open;
• and
• a resilient return member holding the annular valve member in its closed position and allowing said valve member to open above a predetermined threshold in a very short time.