Pressure cap for cooling system having variable opening pressure

A pressure cap for a cooling system having variable opening pressure, which is applied to the cooling system for circulating cooling water to radiate heat generated by an engine of a vehicle, and maintains an inside pressure of the cooling system in a predetermined range, the pressure cap structure comprising:

• a positive pressure spring mounted in a valve body, and operated to connect the cooling system to an outside when the inside pressure of the cooling system rises;
• and
• a shape memory polymer restored to an initial shape thereof when reaching a predetermined temperature, and mounted between the positive pressure spring and a spring guard supporting the positive pressure spring,
• a cover member mounted to directly cover an end of the shape memory polymer, wherein the cover member is assembled into the spring guard,
• wherein the shape memory polymer is extended before reaching a boiling temperature of the cooling water and compressed from the initial shape of extension when reaching the boiling temperature of the cooling water, and
• wherein shape memory polymer is injection-molded in a state where a lower portion of the positive pressure spring is inserted into a body of the shape memory polymer.