Timing belt tensioner

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.

FIELD OF THE INVENTION

The present invention relates to a tensioner for tensioning a flexible drive means, such as a timing belt, timing chain or the like, on an engine. More specifically, the present invention relates to a tensioner for a flexible drive means which can be installed on an engine in a relatively easy manner.

BACKGROUND OF THE INVENTION

Tensioners for flexible drive means, such as timing belts, timing chains and the like, are well known in the art. The tensioner includes a rotatable member, typically a roller or pulley, which is biased against the belt to maintain a substantially constant tension in the belt as the engine is operated. The pulley is pivotally mounted to the tensioner at a mounting point which is spaced from the axis about which the pulley rotates to create an eccentric about which the pulley can be moved to tension the belt. The difference between the pivotal mounting point and the axis of rotation for the pulley is typically referred to as the “arm” of the tensioner and a spring or other biasing means biases the pulley towards the belt to tension it.

As the forces applied to the belt by the engine can vary significantly as the engine operates, resulting in significant changes in the tension in the flexible drive member, the biasing force which biases the pulley of the tensioner against the belt must be relatively large. Tensioners thus typically include a spring having a relatively large spring force constant to bias the pulley against the belt.

A consideration in the design of tensioners is the angle, with respect to the arm, at which the belt contacts the pulley. Ideally, the contact force between the belt and the pulley should be orthogonal, or close to orthogonal to the arm to achieve proper tensioning as the effective biasing force created by the spring will vary significantly as the contact force angle approaches an angle where the force is inline with the arm, rather than orthogonal to it.

While the above considerations can be effectively dealt with in the design of the tensioner, it can be difficult to install the resulting tensioner on the engine, as taught by commonly assigned U.S. Pat. No. 5,919,107. Specifically, it can be difficult to mount the tensioner on the engine while positioning the arm of the tensioner to achieve the desired angle between the arm and the contact force between the belt and the pulley and while achieving the necessary preload on biasing spring.

Prior attempts to provide a tensioner which can be installed in a reasonable manner have included commonly assigned U.S. Pat. No. 6,149,542, which provides a tensioner with an operating eccentric and an installation eccentric. The installation eccentric is employed to move the tensioner to a position sufficiently far away from the belt to allow installation and routing of the belt. Once the belt is installed, the tensioner is moved along its installation eccentric to place the tensioner into the operating position after which the tensioner arm can move about the operating eccentric.

Typically, the movement of the tensioner along the installation eccentric during installation requires a two-handed operation on the part of the installer wherein the mounting bolt (or bolts) fastening the tensioner to the engine must be loosened with a first hand while the tensioner is moved through its installation eccentric to the desired operating position with the second hand. Once the desired operating position is obtained, the mounting bolt or bolts are fastened with the first hand while the tensioner is held at the operating position with the second hand. As is apparent, this can be an awkward and/or difficult operation to perform. However, even more problematic is the fact that, as the mounting bolt or bolts of tensioner must be loosened during the setting of the operating position, the tensioner can be tilted with respect to the face of the engine. Any such tilt will result in tensioner being set at an improper operating position which will not be apparent until the tensioner mounting bolt or bolts are tightened. In such a case, the installer must re-perform the installation operation until a correct operating position is obtained.

Prior art attempts to avoid installation difficulties have included tensioners with relatively expensive components such as one way clutch mechanisms in single eccentric long-arm tensioners.

It is desired to have a tensioner which is relatively easy to install and which avoids the need for relatively expensive components.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel tensioner for a belt which obviates or mitigates at least one disadvantage of the prior art.

According to a first aspect of the present invention, there is provided a tensioner for a belt on an engine. The tensioner has a pivot shaft having a central bore to receive a bolt to install the tensioner to the engine. A tensioner arm is rotatably mounted on the pivot shaft and has a cylindrical bearing mounting surface with its center located eccentrically with respect to the center of the pivot shaft. A rotatable member is rotatably mounted to the cylindrical bearing mounting surface. The rotatable member has an outer surface complementary to the surface of belt to be contacted. A spring is operable to bias the tensioner arm about the pivot shaft to move the rotatable member towards the belt to tension the belt. An adjustable stop means receives a stop member of the tensioner arm and defines a range through which the stop member, and thus the tensioner arm, can move during operation of the tensioner. The stop means is moveable by an installer of the tensioner after the tensioner has been installed on the engine to alter the angular position of the range of movement of the tensioner arm from a position suitable for installation of the tensioner to a position suitable for operation of the installed tensioner.

Preferably, the stop means includes indicia to indicate when the tensioner arm and the stop means have been moved to the suitable operating position. In one embodiment, the tensioner includes a base and the spring has one end attached to the tensioner arm and the other end attached to the base.

According to a second embodiment, the spring has one end attached to the tensioner arm and the other end attached to the stop means, such that the tension in the spring is compensated for movement of the tensioner arm, as the stop means is moved.

DETAILED DESCRIPTION OF THE INVENTION

A tensioner in accordance with the present invention is indicated generally at20inFIG. 1. Tensioner20includes a base24, a tensioner arm28and a biasing spring32which acts between base24and tensioner arm28. One tang36of biasing spring32engages a slot40in base24while the other tang44engages a spring slot or hole at the top section of a bore48in tensioner arm28to bias tensioner arm28in the direction shown by arrow52.

As best seen inFIG. 2, tensioner arm28includes a central bore56and a pivot shaft60. Central bore56receives a bushing58. Pivot shaft60has a center bore62through which a bolt (not shown) is passed to fasten tensioner20to an engine. Bushing58allows tensioner arm28to rotate about pivot shaft60.

Tensioner20further includes a rotatable member64which is designed to engage the flexible drive means to be tensioned. In the embodiment of tensioner20illustrated in the Figures, the flexible drive means to be tensioned is a toothed belt and rotatable member64is a pulley that features a smooth outer surface which is intended to engage the outer surface of the toothed belt.

However, as will be apparent to those of skill in the art, the present invention is not limited to tensioners to engage the outer (smooth) surface of toothed belts. The present invention can be employed to engage the inner (toothed) surface of a toothed belt, to engage the inner or outer surface of a smooth belt and/or to engage the inner or outer surface of a chain. For each different configuration, tensioner20need only have the outer surface of rotatable member64shaped in a manner complementary to the particular surface of the particular flexible drive means to be tensioned. For example, if the flexible drive means to be tensioned is a chain drive, the outer surface of rotatable member64can be in the form of a sprocket with suitably sized and spaced teeth to engage the chain. Other configurations and shapes for the outer surface of rotatable member64will be apparent to those of skill in the art.

In the illustrated embodiment rotatable member64, best seen inFIG. 5, is a pulley and includes an integral bearing to allow pulley64to rotate with respect to tensioner arm28. Specifically, pulley64includes an inner race74, bearing balls and cages72and outer ring which are integrally formed with the above-mentioned smooth outer pulley surface of pulley64which engages the belt. Inner race74is fitted on cylindrical bearing mounting surface68of tensioner arm28thereby allowing the outer pulley surface to rotate about the centre axis70of bearing mounting surface68of tensioner arm28.

As will be apparent to those of skill in the art, pulley64need not be formed with an integral bearing and, instead, pulley64can comprise a pulley and any suitable separate bearing can be provided to act between cylindrical bearing mounting surface68and pulley64.

As is best seen inFIG. 3, the center axis70of bearing mounting surface68is spaced or offset from the center axis71of center bore56such that, as tensioner arm is rotated about pivot shaft60, bearing mounting surface68and pulley64will follow an eccentric path with respect to the center axis71of center bore56, thus moving pulley64towards or away from the flexible drive member to be tensioned.

A thrust washer80is provided between the upper surface of tensioner arm28and a flange84on pivot shaft60to handle axial loads between tensioner arm28and pivot shaft60.

The upper surface of tensioner arm28includes a stop pin92which extends upward from tensioner arm28, through thrust washer80and engages an arcuate slot96in a stop plate100. The range of the rotation of tensioner arm28about pivot shaft60is limited by stop pin92abutting one or the other end ends of slot96.

In the illustrated embodiment, end104of slot96is the “free arm” stop and limits the extent to which pulley64can move towards the belt to tension it and end108of slot96is the “backstop” which limits the extent to which tensioner arm28and pulley64can move away from the belt (clockwise in the illustrated embodiment) to the point where excessive dynamic vibrations of the drive system, or even tooth skip failure, could occur.

Stop plate100frictionally engages pivot shaft60with a frictional force such that during installation, as described below, stop plate100can be rotated by the installer about pivot shaft60, overcoming the frictional force, to alter the angular position of stop plate100relative to the stationary parts, such as pivot shaft60and base24of tensioner20, but the frictional force is sufficient to resist rotation of stop plate100about pivot shaft60during normal operation of engine it is installed on.

Pivot shaft60is connected to, preferably press fit into, base24such that sufficient frictional force is developed between base24and pivot shaft60to prevent rotational movement between pivot shaft60and base24during handling of the tensioner20.

In a present embodiment of the invention, stop plate100frictionally engages, preferably by press fit, pivot shaft60to obtain an interference fit therebetween. The resulting frictional force produced between stop plate100and pivot shaft60is sufficiently large that the expected operating loads on tensioner arm28are insufficient to rotate stop plate100about pivot shaft60. However, the resulting frictional force can be overcome by the installer of tensioner20, by attaching a wrench or other tool to stop plate100and exerting force on stop plate100thereby.

It is contemplated that in some circumstances it may be desired to employ friction enhancers (such as Locktite™ or any other suitable material) between stop plate100and pivot shaft60.

A pair of tool holes102is provided in stop plate100to allow a tool with a complementary set of pins to engage tool holes102to rotate stop plate100as desired. As will be apparent to those of skill in the art, the present invention is not limited to the use of such a two-pin tool and any other suitable means by which an installer can rotate stop plate100can be employed.

When tensioner20is assembled at the factory, stop plate100can be rotationally positioned on pivot shaft60placing the tensioner in an install condition, such that stop pin92abuts end104(due to the biasing of spring32) of slot96positioning tensioner arm28and pulley64to have a minimum amount of offset relative to the base24. In this condition, the pulley can be positioned as far away from the expected position of the flexible belt as possible, enabling easy training of the belt about the pulley64. This allows tensioner20to be installed on an engine, with pulley64being free of the belt, by inserting a bolt through central bore62of pivot shaft60and torquing the bolt to a specified value. An index tab110extends from the bottom of base24and engages a complementary slot of groove on the engine to properly position tensioner20in a correct angular position on the engine.

Once tensioner20is fastened to the engine and the belt has been properly routed over all other elements of the drive system, the installer of tensioner20rotates stop plate100(clockwise in the illustrated embodiment) which allows spring32to rotate tensioner arm28about bushing58to move pulley64towards the belt.

As pulley64contacts the belt, the installer continues rotating stop plate100and end104of slot96moves away from stop pin92as the belt prevents further rotation of tensioner arm28and stop pin92. The installer continues to rotate stop plate100until stop pin92is aligned with indicia112provided on stop plate100. Indicia112, which can be a scored line, painted indicator or any other suitable indicia, is located at a predetermined position along slot96wherein tensioner arm28and pulley64are in a nominal position where ends104and108provide appropriate stops for the desired range of movement of tensioner arm28and pulley64during operation of the engine. The position of indicia112along slot96is predetermined at the factory, using well known techniques, for each different engine on which tensioner20is to be installed. At this nominal operating position the pulley can move towards, or away from, the belt within a range that is limited to the expected operating needs of the belt.

In many prior art tensioners, the tensioner could only be moved from an installation position to an operating position prior to the mounting bolts being torqued to the required fastening values, thus leading to the possible mis-adjustment of the tensioner due to a tilt of the tensioner with respect to the belt. In contrast, tensioner20is adjusted from the installation position to the operating position after tensioner20is completely mounted to the engine, with the mounting bolt torqued to the final value.

Further, unlike many prior art tensioners, adjustment of tensioner20is a one-handed operation, only requiring the rotation of stop plate100, with an amount of mechanical advantage via an appropriate tool, and is thus simpler and faster to perform that prior art tensioners that required the installer to simultaneously manipulate an operating range setting bolt and a mounting bolt.

Thus, unlike prior art tensioners, tensioner20can be simply and accurately installed without requiring expensive or complex components, such as one way clutches or the like.

Another embodiment of the present invention is illustrated inFIGS. 6 through 8. While tensioner20provides several advantages over prior art tensioners, if the range of movement of tensioner arm28between the installation position and the operating position is relatively large, it can be difficult to size spring32to provide the desired degree of control of the force being applied to the belt. This is due to the fact that the spring force of spring32is not constant, as it changes somewhat as spring32is wound and unwound. Accordingly, if spring32is wound and unwound to a relatively large extent as tensioner20is moved between the installation and operating positions, it can be difficult to ensure that spring32is properly tensioned to create the desired biasing force on tensioner arm28.

In the embodiment ofFIGS. 6 through 8, wherein like components to those of the embodiment shown inFIGS. 1 through 5are indicated with like reference numerals with an “a” appended.FIGS. 6 through 8show the assembly of a different base24aand stop plate200which is used with the remainder of the components of tensioner20, described above, wherein stop plate100and stop pin92are supplanted by the illustrated assembly. In this embodiment, the tension of spring32aremains relatively constant as tensioner arm28is moved between the installation position and the operating position.

Specifically,FIG. 6shows a base24awhich includes a stop plate200. In the illustrated embodiment, stop plate200is press fit to a central upraised cylindrical boss204to form an interference fit which produces a frictional force between stop plate200and boss204to inhibit rotation of stop plate200about boss204. As was the case with the embodiment discussed above, it is contemplated that in some circumstances it may be desired to employ friction enhancers between stop plate200and boss204. Pivot shaft60is received in the interior of boss204.

As will be apparent to those of skill in the art, stop plate200can be frictionally mounted to base24ain a variety of manners and the present invention is not limited to the attachment of stop plate200via a cylindrical boss204. It is also contemplated that stop plate200can be directly attached to pivot shaft60, rather than to base24a.

Stop plate200includes a slot208which receives tang36aof spring32aand base24aincludes a elongated slot in its outer wall through which tang36aextends and which allows tang36ato be rotated with stop plate200, as described below. Stop plate200further includes a feature to allow the installer to rotate stop plate200during the installation process. In the illustrated embodiment, this feature is in the form of an adjustment arm212which extends outwardly through another slot in the exterior wall of base24abut the present invention is not limited to such an adjustment arm212and any other suitable mechanism for rotating stop plate212, as will occur to those of skill in the art, can be employed.

As will be apparent, tensioner20is assembled at the factory with stop plate200in an installation position, as illustrated inFIG. 6. In this position, free arm stop216abuts abutment surface224and tensioner arm28awill be in its installation position being located at the farthest distance from the belt to allow for installation. As was the case with the previous embodiment, tensioner20is mounted to the engine with a bolt through the central bore62aof pivot shaft60aand the bolt is torqued to a specified value.

Once tensioner20has been properly mounted to the engine, the installer moves adjustment arm212in a counterclockwise direction (in the illustrated configuration) using any suitable tool, moving stop plate200to the position illustrated inFIG. 7where tensioner arm28a, together with pulley64(not shown) are moved towards the belt until pulley64contacts the belt. The frictional force between stop plate200and boss204is large enough to inhibit rotation of stop plate200during normal operation of tensioner20but can be overcome by the installer during installation.

The installer continues to move adjustment arm212in a counterclockwise direction until adjustment arm212is aligned with an indicia (not shown) on tensioner arm28awhich indicates that tensioner arm28ais in its nominal operating position, illustrated inFIG. 8. As shown inFIG. 8, abutment surfaces224and228are located at about the mid-point between free arm stop216and backstop220. As will be apparent, the installation and setting of this embodiment of tensioner20is quite similar to that of the embodiment described with respect toFIGS. 1 through 5.

However, unlike the embodiment ofFIGS. 1 through 5, in the embodiment illustrated inFIGS. 6 through 8, tang36aof spring32amoves together with stop plate200thus compensating for the fact that spring tang44a, attached to tensioner arm28a, is also rotated counterclockwise during the installation process. As will be apparent to those of skill in the art, while the provision of this compensation is presently preferred, it is not necessary and the embodiment ofFIGS. 6 through 8can have spring tang36aattached to base24a. For example, in the case that spring tang36ais attached to stop plate200, it is possible to omit base24afrom tensioner20aand to frictionally connect stop plate200to pivot shaft60a. In this case, it is preferable, but not absolutely necessary, to provide a feature on stop plate200to allow the installer to align tensioner20to the correct angular installation position prior to tightening the mounting bolt.

In the embodiment of the present invention illustrated inFIGS. 6 through 8, tensioner arm28aand pulley64attached to it, are held in an installation position, away from the belt, by stop plate200. It is contemplated that some engine designs may not provide enough space for adjustment arm212to be rotated sufficiently from the installation position to the operating position. In such a case, it is possible to rotate tensioner arm28aso that backstop220approaches abutment surface228of stop plate200and to lock tensioner arm28ain this position by an installation pin (not shown) which prevents relative movement between tensioner arm28aand stop plate200. Such installation pins are known to those of skill in the art and are employed with various prior art tensioners.

The location of the installation pin on tensioner20ais preferably selected such that it will be easy for the installer to remove the pin after the belt and/or tensioner20ahas been installed. As an example, the installation pin could be installed through a hole in tensioner arm28a, similar to hole48shown inFIGS. 1 and 2. After going through the hole in the tensioner arm28a, the pin must further engage in a hole or slot-type feature either in stop plate200or base24aor both. After removing the installation pin the installer continues the installation process, as described above, by rotating adjustment arm212in the same way as previously described.

The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.