In a ring-type tensioner, the ring is used to effect a ratcheting action, enabling the plunger to advance, but restricting retracting movement of the plunger. An annular portion of the ring is disposed in a circumferential groove formed in the wall of the plunger-accommodating hole, and a manipulating portion of the ring typically extends outward from the housing so that the ring can be expanded by a tool in the assembly or maintenance of the tensioner.
Typical ring type tensioners are disclosed in Japanese laid-open Patent Applications 2002-5249, published on Jan. 9, 2002 and 2001-146946, published on May 29, 2001.
In the maintenance of an engine, there are occasions in which it is necessary to release the tension in the engine timing chain. If tension in the chain is maintained by a ring-type tensioner, the plunger of the tensioner can be allowed to retract by expanding the elastic ring, using an expansion tool to effect relative movement of manipulation elements that protrude from the annular portion of the ring. Often, there is little working space in the vicinity of the tensioner when installed on an engine, and it is difficult to expand the ring using a conventional expansion tool. In addition it is frequently necessary to insert the expansion tool through a small access hole in a cover of an enclosure, such as a timing chain cover.
In the tensioner of Japanese Patent Application 2002-5249, parts of the ring cross each other, and a pinching tool is used to expand the ring. Not only is it difficult to reach the manipulation elements with the pinching tool, but it is also difficult to maintain the ring in its expanded condition using the pinching tool.
When the elastic ring is the type of ring in which the manipulation elements protrude from parts of the ring that do not cross each other, as in Japanese Patent Application 2001-146946, the ring is expanded by inserting a tool between the manipulation elements. A special, dedicated, manipulation tool is required. Moreover, because the positions of the manipulation elements may change due to rotation of the ring, it can be difficult to insert a manipulation tool between the pair of manipulation elements.
In the type of the tensioner in which the elastic ring is formed with parts that cross each other and has an asymmetric shape, as in Japanese Patent Application 2002-5249 for example, it is difficult to automate the manufacture of the ring, and difficult to supply the ring using a parts feeder especially because the ring tends to become entangled with other rings.
In addition, in a ring in which the parts from which the manipulation elements extend cross each other, the manipulation pieces can bend when the manipulation elements are pinched to expand the diameter of the ring, sometimes making it difficult to expand the ring to the extent required to release the plunger.
Accordingly, there is a need for a ring-type tensioner in which the plunger can be installed more easily and efficiently in the tensioner housing, and in which the plunger can be released more easily and efficiently for maintenance,
There is also a need for a ring-type tensioner in which the elastic ring can be installed more easily and efficiently into the tensioner housing.