Hydraulic shock absorber

A hydraulic shock absorber comprising:

• a cylinder assembly;
• a sealing head fixed to one end of the cylinder assembly;
• a piston assembly including a piston reciprocatively inserted into the cylinder assembly and a piston rod secured to the piston so as to pass through the sealing head;
• a foot valve assembly housed in the cylinder assembly near the other end thereof;
• a first chamber defined by the cylinder assembly, sealing head and piston;
• a second chamber defined by the cylinder assembly, piston and foot valve assembly;
• a third chamber defined by the foot valve assembly and the other end of the cylinder assembly;
• a damping oil filled in the first, second and third chambers;
• first undamping passage means formed in the piston assembly to establish communication between the first and second chambers;
• first check valve means for allowing the free flow of damping oil from the second chamber into the first chamber through the first undamping passage means when the piston rod enters the first chamber;
• first damping passage means formed in the piston assembly to provide communication between the first and second chambers, said first damping passage means including a first damping passage provided with a first opening-variable orifice and communicating at its one end with the first chamber, a second damping passage communicating at its one end with the other end of said first damping passage and a third damping passage provided with a first opening-fixed orifice, said third damping passage communicating at its one end with the other end of the first damping passage and at its other end with the second chamber;
• a first heat-sensitive valve unit for changing the opening area of the first opening-variable orifice as a function of the temperature of damping oil;
• said first heat-sensitive valve unit is manually adjustably coupled to the piston assembly so as to change the initial opening area of the first opening-variable orifice;
• second check valve means for allowing restricted flow of damping oil from the first chamber into the second chamber through the first and second damping passages when the first chamber has a higher pressure by a predetermined extent than the second chamber;
• second undamping passage means formed in the foot valve assembly to establish communication between the second and third chambers;
• third check valve means for allowing the free flow of damping oil from the third chamber into the second chamber through the second undamping passage means when the piston rod is withdrawn from the first chamber;
• second damping passage means formed in the foot valve assembly to provide communication between the second and third chambers, said second damping passage means including a fourth damping passage provided with a second opening-variable orifice and communicating at its one end with the second chamber, a fifth damping passage communicating at its one end with the other end of the fourth damping passage and at its other end with the third chamber, and a sixth damping passage provided with a second opening-fixed orifice, said sixth damping passage communicating at its one end with the other end of the fourth damping passage and at its other end with the third chamber;
• a second heat-sensitive valve unit for changing the opening area of the second opening-variable orifice as a function of the temperature of the damping oil;
• said second heat-sensitive valve unit is manually adjustably coupled to the foot valve assembly so as to change the initial opening area of the second opening variable orifice;
• fourth check valve means for allowing restricted flow of damping oil from the second chamber into the third chamber through the fourth and fifth damping passages when the second chamber has a higher pressure by a predetermined extent than the third chamber;
• and
• a reservoir filled with damping oil and communicating with the third chamber.