Patent ID: 8197369

Claim:
A hydraulic tensioner having a pressure relief valve mechanism for an engine having engine stages, including at least an idle stage, normal operation stage, and chain resonance stage, the tensioner comprising: a plunger for pressing against a chain; a housing that has a plunger bore to slidably receive the plunger and that has a spool bore having at least one inner relief aperture in communication with the plunger bore and at least two outer relief apertures connecting the spool bore to an outside of the housing; a hydraulic chamber formed between the plunger bore and the plunger having an inlet for receiving fluid from a source of pressurized oil; and a spool valve comprising a spool that is slidably supported in the spool bore, the spool being moveable within the spool bore by oil pressure from the source of pressurized oil through the inlet, between at least three positions corresponding to the idle stage, the normal operation stage, and the chain resonance stage of the engine; wherein when the spool is in the position corresponding to the idle stage, the spool blocks fluid flow from the at least one inner relief apertures to the at least two outer relief apertures; wherein when the spool is in the position corresponding to the normal operation stage, one of the at least two outer relief apertures is in fluid communication with the at least one inner relief aperture through the spool bore, connecting the plunger bore to the outside of the housing; and wherein when the spool is in the position corresponding to the chain resonance stage, at least two outer relief apertures are in fluid communication with at least one inner relief aperture through the spool bore, connecting the plunger bore to the outside of the housing.