Hydraulic hinge having rotatable shaft and linearly movable plug forming fluid chambers

A hydraulic hinge comprising:

• a cylinder having an inside diameter defining a front open end and a rear open end respectively sealed by a front cap and a rear cap;
• an elongated shaft rotatably inserted into said cylinder from the front open end thereof through a hole formed on said front cap to have a front portion of said shaft extend out of said cylinder;
• a circumferential space defined between the inside diameter of said cylinder and said shaft to be filled with a hydraulic fluid;
• a plug fit into said circumferential space to divide said circumferential space into a first chamber and a second chamber, said plug being secured to said shaft by securing means in such a way to be rotatable in unison with but linearly movable relative to said shaft and said plug being engageable with the inside diameter of said cylinder by engaging means in such a way to allow said plug to be movable relative to said cylinder so that when said shaft is rotated, said plug rotates therewith and linearly moves relative to said cylinder and said shaft to change sizes of said first and second chambers;
• a first fluid passage formed inside said shaft to provide a fluid communication between said first chamber and second chamber, said first fluid passage having such a cross-sectional dimension to allow the hydraulic fluid to flow between said first and second chambers at a first flow rate;
• a second fluid passage formed inside said shaft connecting between said first and second chambers, said second fluid passage having checking means mounted therein to prevent the hydraulic fluid from flowing from said first chamber into said second chamber and only allows the hydraulic fluid to flow from said second chamber to said first chamber at a second flow rate greater than said first flow rate;
• and
• when said shaft is rotated along a first angular direction, said plug moves inside said circumferential space relative to said cylinder in a first linear direction to reduce the size of said first chamber and increase the size of said second chamber so as to force the hydraulic fluid to flow from said first chamber to said second chamber at the first flow rate and thus controlling said shaft to rotate at a first rotational speed;
• and when said shaft is rotated along a second angular direction, opposite to the first angular direction, said plug moves inside said circumferential space relative to said cylinder in a second linear direction, opposite to the first linear direction, to increase the size of said first chamber and reduce the size of said second chamber so as to force the hydraulic fluid to flow from said first chamber to said second chamber at the second flow rate and thus controlling said shaft to rotate at a second rotational speed which is greater than the first rotational speed due to the fact that the second flow rate is greater than the first flow rate.