Hydraulic tensioner

A chain tensioner comprising:

• a housing;
• a plunger-accommodating hole formed in the housing, the plunger accommodating hole having a bottom at one end thereof and an opening at an end thereof opposite from said bottom;
• a plunger having a hollow interior, the plunger being slidable in the plunger-accommodating hole, along a plunger-accommodating hole axis, and protruding from said plunger-accommodating hole through said opening for maintaining tension in a traveling transmission chain;
• a high-pressure oil chamber formed by the housing and the hollow interior of the plunger;
• a check valve unit arranged to allow oil to flow into the high pressure oil chamber while blocking reverse flow of oil from the high-pressure oil chamber;
• a plunger-biasing spring within the high-pressure oil chamber urging the plunger in a protruding direction;
• and
• a deaeration mechanism provided adjacent the bottom of the plunger-accommodating hole for bleeding air from the high-pressure oil chamber to the exterior of the housing;
• the deaeration mechanism comprising;
• a threaded hole formed in the housing, said threaded hole having an outer end opening in an outer surface of the housing and an inner end opening in the high pressure oil chamber, and extending from said outer end opening to said inner end opening along a hole axis parallel to said plunger-accommodating hole axis, the threads of the hole having an axially outward facing flank and an axially inward facing flank;
• a deaeration regulating screw having a head and being threaded into the threaded hole, the screw also having threads with an axially outward facing flank and an axially inward facing flank;
• and
• a deaeration regulating washer positioned against a part of said outer surface of the housing surrounding said outer end opening of the threaded hole;
• wherein the deaeration regulating washer is a spring washer arranged to exert a force on the screw urging the screw in an outward direction from said threaded hole;
• wherein a helical orifice providing fluid communication between the high pressure oil chamber and the exterior of the housing is formed by a clearance between the axially inward facing flank of the screw threads and the axially outward facing flank of the threads of the threaded hole;
• and
• wherein a deaeration guide groove is formed in said part of said outer surface of the housing surrounding the outer end opening of the threaded hole, said deaeration guide groove extending from an air-receiving end at which the deaeration guide groove meets said helical orifice to an air exit end remote from said helical orifice, said air exit end being disposed at a level above the level of said air-receiving end, and said deaeration guide groove providing a path for the flow of air, bled from the high pressure oil chamber through the helical orifice, past the washer to the exterior of the housing.