Shock absorbing method and apparatus

An apparatus for damping reactive displacement oscillations of a sprung mass in a system including a spring shock absorber interposed between the sprung mass and an unsprung mass, wherein such oscillations occur in response to an impact force applied to the unsprung mass and transmitted to the sprung mass through the spring shock absorber, comprising:

• controllable damping means for providing a first damping mode having a first damping coefficient and for providing a second damping mode having a second damping coefficient that is substantially greater than said first damping coefficient;
• sensing means for sensing the application of an impact force to the unsprung mass;
• and
• control means for initially causing said damping means to assume said first damping mode and for responding to said sensing means for causing said damping means to assume said second damping mode after a time delay from said application of an impact force to the unsprung mass, said control means including a delay means for causing the duration of said time delay to substantially equal the time interval required for the sprung mass to complete a first cycle of its reactive displacement oscillations.

In an aircraft landing gear shock strut of the type including a cylinder and a piston in which the piston is arranged for reciprocation in the cylinder between extended and compressed positions, and pneumatic spring means responsive to the reciprocation of the piston in the cylinder for developing a spring force urging the piston towards its extended position, and hydraulic means for damping the reciprocation of the piston in the cylinder, the combination therewith comprising:

• sensing means for sensing an initial displacement of said piston from its extended position toward its compressed position in reaction to touchdown of a landing aircraft, said sensing means including means for producing an electrical timing signal indicating the time of said initial displacement;
• fluid control means for providing first and second damping modes in association with said hydraulic means, said first mode providing a first predetermined damping coefficient and said second mode providing a second predetermined damping coefficient that is substantially greater in value than said first predetermined damping coefficient;
• and
• timing control means including signal delay means for delaying said timing signal by a predetermined time delay and causing said fluid control means to initially assume said first mode and for responding to said timing signal after it has been delayed by said delay means for causing said fluid control means to assume said second mode after said predetermined time delay, said predetermined time delay provided by said delay means being substantially equal the time interval that is defined by the duration of a first reactive cycle of compression and reextension of said piston in said cylinder in response to an impact force associated with the touchdown of the landing aircraft.

In a method of absorbing the impact of a force, abruptly applied to a mass, by interposing a spring between the applied force and the mass such that the spring undergoes oscillatory displacement in reaction to the abruptly applied force and wherein the amplitude of such displacement decays with time, the improvement comprising:

• sensing the application of said applied force;
• initially damping the displacement of the spring with a damping coefficient that has a first predetermined value;
• after a predetermined time delay from the step of sensing, damping the displacement of the spring with a damping coefficient that has a second predetermined value that is greater than the first value;
• and,
• said time delay being substantially equal to the time interval that is defined by the time duration required for the spring to complete a first cycle of said oscillatory displacement.