Variable stiffness function through a check valve in a hydraulic

A hydraulic tensioner for an internal combustion engine for tensing a span of a chain or a belt comprising:

• a housing having a bore with a first open end in communication with a fluid input, and a second closed end;
• a hollow piston slidably received within the bore of the housing, the piston comprising a body having an open end and a closed end, a bottom surface at the open end, a top surface at the closed end, a fluid inlet between the open end and the closed end, and a hollow bore defining an internal reservoir in communication with the fluid input through the fluid inlet of the body of the piston;
• a hydraulic pressure chamber defined by the hollow bore of the body of the piston, and between the open end of the body of the piston and the second closed end of the bore of the housing;
• a piston spring received within the hydraulic pressure chamber for biasing the piston away from the second closed end of the bore of the housing;
• a check valve assembly received within the hollow bore of the body of the piston between the internal reservoir and the hydraulic pressure chamber, the check valve assembly comprising:
• a U-shaped retainer defining a cavity and having at least one retainer opening and axially extending flanges;
• a moveable member received within the cavity;
• a check valve spring received within the cavity and between the moveable member and the retainer;
• a valve seat having axially extending flanges and defining a seat opening, the valve seat nesting within the cavity of the retainer, such that the axially extending flanges of the valve seat are adjacent the axially extending flanges of the retainer;
• a check valve vent washer comprising:
• an outer circumference with a plurality of spaced apart legs and a plurality of openings;
• and
• an inner circumference in fluid communication with the outer circumference through the plurality of openings, the inner circumference comprising:
• a concentric interior well connecting the plurality of openings to a vent reservoir, a central ring defining a central hole in communication with the internal reservoir, the central ring comprising a vent groove connecting the vent reservoir to the central hole;
• wherein, in a first position, the moveable member is biased against the disk seat by the check valve spring, sealing the seat opening, preventing fluid from passing from the internal reservoir to the hydraulic pressure chamber and in a second position, the moveable member is biased against the check valve spring, such that fluid can flow from the internal reservoir to the hydraulic pressure chamber through the seat opening;
• wherein when the check valve assembly is in the first position, fluid from the high pressure chamber leaks into at least one of the plurality of openings, into the concentric interior well, into the internal reservoir to the vent groove and to the central hole in fluid communication with the internal reservoir.