Patent Description:
Belt tensioners are generally well known devices that have been used previously in many belt-drive systems. It is conventional practice to use a tensioner to apply a constant belt-tensioning force, which compensates for increases in belt length due to wear and other factors. A common type of conventional belt tensioner has a fixed structure and a pivoted structure eccentrically mounted on the fixed structure by means of a pivot assembly, and the pivoted structure has a belt-engaging pulley rotationally mounted on it. A coil spring surrounds the pivot assembly and has its ends connected between the fixed and pivoted structures so as to bias the pivot structure in a belt take-up direction. As the pivoted structure moves from a position of minimum belt take-up to a position of maximum belt take-up, the spring biasing force decreases. Despite this varying spring force over the range of tensioner movement, substantially constant belt tension is maintained by the tensioner.

Various techniques are currently used to properly install timing belt tensioners on engines. One of the most commonly used techniques is to construct the tensioner with an eccentric adjusting member that forms part of the fixed structure; the eccentric adjusting member is rotated around the tensioner mounting bolt and thus moves the tensioner away from the belt (to allow the belt to be routed into the drive system) or towards the belt (to apply tension in the drive system). A typical installation procedure when using the current standard design includes mounting the tensioner on the engine with the eccentric member in the extreme position away from the belt, routing the belt into the drive system, rotating the eccentric member towards the belt until the tensioner reaches the nominal operating position, and locking the tensioner with the mounting bolt.

Representative of the art is <CIT> which discloses a tensioner for tensioning a flexible drive means, such as a timing belt or chain, includes a pulley to contact the belt. The pulley is mounted on a tensioner arm and the tensioner arm can be rotated about a pivot shaft mounted to the tensioner by a spring. The axis about which the pulley rotates is spaced from the axis of the rotation of the tensioner arm with respect to the pivot shaft and the spacing of these axes of rotation results in the pulley moving through an eccentric towards or away from the belt when the tensioner arm is rotated. A stop is used to limit the range of movement of the tensioner arm between a desired range of movement defined by a free arm stop and a backstop. The position of the stop is adjustable by an installer. The angular range of movement of the tensioner arm is adjustable from a position suitable for installation of the tensioner to a position suitable for operation of the installed tensioner. In one embodiment, the movement of the stop from the installation position to the nominal operating position also compensates the spring.

<CIT> discloses an eccentric tensioning device for tensioning the traction means of a drive. The tensioning device includes a track roller device, which has a running disk and a rolling bearing for supporting this disk, a work eccentric for supporting the track roller device so that it can be displaced in a radial direction relative to the axis of the rolling bearing through pivoting of the work eccentric, a torsion spring for pre-tensioning the work eccentric, and a fixing device for securing the work eccentric in a mounting position, in which the torsion spring is located in a pretensioned state. The fixing device can be brought into a released state during attachment of the eccentric tensioning device to a flange surface, in which the running disk is forced radially relative to the rotating axis of the rolling bearing against the associated traction means due to the work eccentric.

<CIT> discloses an eccentric pivot arm tensioner capable of automatic belt tensioning and operating range indexing during installation. The tensioner comprises a stop plate and cooperating lock plate, and a pivot arm having a pivot arm member that cooperatively engages a base plate member. In a transit mode, the pivot arm member temporarily engages the base plate member to put a torsion spring and thereby the pivot arm in a preloaded condition. The lock plate is engaged with the stop plate. As a mounting fastener is engaged into a mounting surface the pivot arm member is automatically disengaged from the base plate member by an axial movement of the pivot arm, thereby allowing the pivot arm to rotate and impart a torsion spring force to a belt. During the initial movement the lock plate remains engaged with the stop plate thereby causing the lock plate to rotate with the pivot arm, which automatically and properly indexes the pivot arm movement travel stop members with respect to the lock plate. As the fastener is fully torqued down, the lock plate is fully disengaged from the pivot arm and fixed in position.

What is needed is a tensioner having a first axial member extending from the pivot arm, the first axial member comprising a radially projecting portion adjacent to a radially receding portion, and the radially projecting portion engaging a radially projecting tab in a first pivot arm position and the radially receding portion cooperating with the radially projecting tab in a second pivot arm position. The present invention meets this need.

The present invention provides a tensioner as recited in claim <NUM>. Optional features are recited in the dependent claims.

Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention.

<FIG> is an exploded view. Tensioner <NUM> comprises a base <NUM>, pivot arm <NUM> and pulley <NUM>.

A torsion spring <NUM> is disposed between base <NUM> and pivot arm <NUM>. Pulley <NUM> is journalled to pivot arm <NUM> on a bearing <NUM>. Torsion spring <NUM> applies a load to the pivot arm which in turn applies a load to a belt (not shown).

Bushing <NUM> is disposed between pivot arm <NUM> and base shaft <NUM>.

Retainer <NUM> engages shaft <NUM>. Retainer <NUM> is held in place in shaft <NUM> by clip <NUM>. Clip <NUM> is engaged within groove <NUM>. When clip <NUM> is engaged with retainer <NUM> pivot arm <NUM> is axially retrained and torsion spring <NUM> is compressed.

Fastener <NUM> is used to mount the tensioner to a mounting surface such as an engine (not shown). Fastener <NUM> projects through retainer <NUM>. During installation fastener <NUM> presses down on retainer flange <NUM>, which in turn presses on pivot arm <NUM>, thereby urging pivot arm <NUM> to move axially relative to base <NUM>.

Pivot arm <NUM> pivots about shaft <NUM> on a bushing surface <NUM>.

Base <NUM> comprises a tab <NUM> which projects radially outward from pivot axis A-A.

Pivot arm <NUM> comprises an axial member <NUM>. Projecting member <NUM> extends in a direction parallel to the pivot axis A-A. Member <NUM> comprises a portion <NUM>. Portion <NUM> recedes radially outward. Portion <NUM> is disposed to cooperatively engage with tab <NUM> for a part of the rotation of pivot arm <NUM>. Member <NUM> further comprises projecting portion <NUM>. Projecting portion <NUM> projects radially inward toward A-A. Radially projecting portion <NUM> is adjacent to radially receding portion <NUM> away from A-A on member <NUM>.

In a first axial position of pivot arm <NUM>, projecting portion <NUM> is at the same position as and adjacent to tab <NUM>, wherein tab <NUM> acts as a stop for pivot arm <NUM> thereby preventing rotation of pivot arm <NUM> in a direction urged by torsion spring <NUM>. In a second axial position of pivot arm <NUM>, projecting portion <NUM> is moved out of alignment with tab <NUM> so that tab <NUM> does not act as a stop for pivot arm <NUM>, thereby allowing pivotal movement of pivot arm <NUM> by action of torsion spring <NUM>.

Base <NUM> comprises a base axial projection <NUM>. Base axial projection <NUM> extends parallel to axis A-A. Base axial projection <NUM> acts as a stop to limit the range of motion of pivot arm <NUM> during operation. Base axial projection <NUM> moves between stop surface <NUM> and stop surface <NUM>.

End <NUM> of spring <NUM> engages slot <NUM> in pivot arm <NUM>.

<FIG> is a cross-section of the tensioner. Clip <NUM> is engaged with retainer <NUM>. Clip <NUM> engages shoulder <NUM> within shaft <NUM>, which prevents retainer <NUM> from pulling out of shaft <NUM> due to the force of spring <NUM>. This in turn retains pivot arm <NUM> on shaft <NUM>. Pivot arm <NUM> has a limited range of axial movement on shaft <NUM>. Torsion spring <NUM> is in a partially compressed state with the tensioner in an assembled condition. A first dimension A1 extends from flange <NUM> to the bottom of base <NUM>.

Pivot axis A-A of pivot arm <NUM> is offset from and parallel to the rotational axis B-B of pulley <NUM>. Pulley <NUM> rotates about axis B-B on bearing <NUM>.

<FIG> is a perspective view of the tensioner. Projecting portion <NUM> is shown adjacent to and engaged with tab <NUM>. This configuration prevents pivot arm <NUM> from rotating with respect to base <NUM>. This is referred to as the un-installed state.

<FIG> is a detail of <FIG>. Projecting portion <NUM> contacts or bears upon tab <NUM> due to the torsional spring force of torsion spring <NUM>. This orientation restricts rotation of pivot arm <NUM>. This is also referred to as the un-installed condition. This configuration is realized with dimension A1.

<FIG> is a cross-section of the tensioner in <FIG>. Fastener <NUM> is engaged with hole <NUM> securing the tensioner to a mounting surface MS. As fastener <NUM> is fully installed, pivot arm <NUM> is pressed toward base <NUM>, whereby dimension A2 is realized. Dimension A2 is less than dimension A1. Retainer <NUM> is also displaced within shaft <NUM> toward base <NUM>. Fastener <NUM> may comprise a bolt, stud, pin or other suitable means.

<FIG> is a side view of the tensioner. As pivot arm <NUM> in a first pivot arm position moves toward base <NUM>, projecting portion <NUM> disengages from tab <NUM> in a second pivot arm position, thereby allowing pivot arm <NUM> to rotate into its installed position. Movement of the pivot arm from the first pivot arm position to the second pivot arm position is in the axial direction which is parallel to axis A-A. In the second pivot arm position alignment of receding portion <NUM> with tab <NUM> allows pivot arm <NUM> freedom of pivotal rotation of the pivot arm. This configuration is realized with dimension A2.

<FIG> is a detail of <FIG>. Tab <NUM> is shown in cooperative relation to receding portion <NUM>, which in turn allows freedom of pivotal rotation of pivot arm <NUM>.

<FIG> is a side view of the tensioner. Projecting portion <NUM> is shown disengaged from tab <NUM>. Pivot arm <NUM> is depicted in the operating position with dimension A2.

<FIG> is a detail of <FIG>. Tab <NUM> passes through receding portion <NUM> during operation.

Claim 1:
A tensioner (<NUM>) comprising:
a base (<NUM>) having a shaft (<NUM>) having a shoulder therein;
a pivot arm (<NUM>) pivotally engaged with the base (<NUM>) about a pivot axis (A-A) and having a pivot arm member (<NUM>);
a torsion spring (<NUM>) disposed between the pivot arm (<NUM>) and the base (<NUM>);
the base (<NUM>) comprising a base member (<NUM>) selectively engagable with the pivot arm member (<NUM>);
the pivot arm member (<NUM>) being selectively engaged with the base member (<NUM>) or disengaged from the base member (<NUM>) according to an axial position of the pivot arm (<NUM>); and
a retainer (<NUM>) engaged with the shaft (<NUM>), the retainer being held in place in the shaft (<NUM>) by a clip (<NUM>) engaged within a groove (<NUM>) on the retainer (<NUM>) wherein, when the clip (<NUM>) is engaged with the shoulder (<NUM>), the retainer is prevented from being pulled out of the shaft (<NUM>) by a force of the torsion spring (<NUM>), the pivot arm (<NUM>) is axially restrained, and the torsion spring (<NUM>) is partially compressed; and characterized by:
the pivot arm (<NUM>) having first and second stop surfaces (<NUM>, <NUM>); and
the base further comprising a base axial projection (<NUM>) extending parallel to the pivot axis (A-A) and movable between the first and second stop surfaces (<NUM>, <NUM>) to act as a stop to limit the range of motion of the pivot arm (<NUM>).