Chain or belt tensioner with a ratchet that deactivates

A tensioner for use with a chain or a belt comprising:

• a housing comprising a piston bore, a spool piston bore in fluid communication with the piston bore, and a housing shoulder between the piston bore and the spool piston bore;
• a piston having a plurality of grooves formed along at least a portion of an outer circumference of the piston, the piston being slidably received within the piston bore and forming a first pressure chamber within the piston bore;
• a piston spring biasing the piston in an outward direction from the housing;
• and
• a spool piston slidably received by the spool piston bore, biased in a first direction within the spool piston bore by a spool piston spring, the spool piston having a cutout of a length defined by a first spool piston shoulder and a second spool piston shoulder;
• an expandable circlip comprising a ring shaped body attached to a first leg and a second leg;
• the expandable circlip having an free state in which the ring shaped body is engaged with the plurality of grooves of the piston, and an expanded state in which when the first leg and the second leg are moved toward each other, the ring shaped body is expanded and disengaged from the plurality of grooves of the piston, the first leg and second leg of the expandable circlip being received within the cutout of the spool piston and the second leg contacting the housing shoulder;
• wherein when fluid is supplied from a second supply to a second pressure chamber in the spool piston bore at an end of the spool piston opposite the spool piston spring, pressure of the fluid in second pressure chamber biases the spool piston against the spool piston spring, and the first spool piston shoulder pushes the first leg of the expandable circlip towards the second leg, expanded the ring shaped body of the expandable circlip, disengaging the ring shaped body of the expandable circlip from the grooves on the outer circumference of the piston;
• such that the piston can move towards the housing and reduce chain load when fluid pressure is reduced in the first pressure chamber during engine shutdown.