Pulley encased tensioner and system

Abstract: A tensioner (20) with a pulley (18) rotatably mounted to a pivot arm (32) that is biased with a compression spring (34). The pulley (18) is generally tube-pan shaped and defines an annular space (44) where the compression spring (34) is located. A belt drive system of the automotive camshaft type that includes the tensioner for maintaining operative belt tension.

Description: The invention relates to a tensioner for an endless power transmission member such as an endless belt, chain or the like as defined in the first part of claim 1. A tensioner of this type is described in US-A-4 696 663. This spring type tensioner biases the position of a pivot arm to which a pulley is rotatably mounted. While the tensioner of the invention may be used in various applications for tensioning an endless power transmission member, it is particularly useful as a compact tensioner in limited space applications for controlling tension of a toothed belt as associated with automotive camshaft drive systems. In an automotive camshaft drive system, a toothed or synchronous belt is entrained around pulleys that include at least two toothed pulleys. One of the pulleys is a crank pulley and the other is a camshaft pulley. An idler pulley such as a backside idler pulley may be pressed against the backside of the belt to effect an installed belt tension. Many automotive drive systems use a fixed idler pulley of the eccentric type where the eccentric pivot for the pulley lies radially inward of a bearing such as radially inward of the inner race of a ball type bearing. Since the pivot is radially inward of the bearing rotational surface, the bearings must be quite large to effect some amount of eccentricity for take up for tensioning a slacked belt. While a fixed eccentric type pulley does not introduce tension changes because of an angular positioning of a pivot arm because the eccentric is fixed, it does introduce another type of tension problem. The problem with a fixed eccentric type pulley is that there is a change in the belt drive pulley center distance between a cold engine such as usually occurs during engine start-up and in a warm or thermally expanded engine such as occurs during normal engine operating temperatures. Thus, the thermal effect is to increase belt tension with engine temperature increases, and conversely, decrease belt tension with decreases in engine temperature. A self-adjusting belt tensioner can overcome such changes in the thermal affect between a hot engine and a cold engine. An example of a self-adjusting timing belt tensioner is disclosed in U.S. Patent No. 4,917,655. This tensioner being of the eccentric type with its pivot radially inward of the bearing surface, has the same disadvantage as a fixed eccentric type pulley and that is it requires a very large bearing. Typically, large bearings are usually more expensive than smaller bearings. Also, in such self adjusting eccentric type tensioners, the length of the pivot arm effecting eccentricity is quite small. The short pivot arm length may limit the amount of available "take-up" and also introduce geometric force effects. Large angle changes of a short pivot arm must somehow be accounted for or balanced (e.g., with changing spring loads) for controlling belt tension. U.S. Patent Nos. 4,551,120 and 4,696,663 offer solutions to the short pivot arm of eccentric type tensioners by providing a longer pivot arm length. This is accomplished by locating the pivot radially outward of the pulley bearing surface. While such tensioners are compact, they are designed for front end accessory drive systems instead of timing belt systems and they have an axial length along the pivot axis which is quite deep. Such tensioners use a helically wound torsional spring to bias the positioning of the pivot arm. A housing for containing the torsional spring accounts for a large axial length. The axial length would make them unsuitable for some automotive belt tensioning applications because of insufficient space. Another type of belt tensioner is disclosed in US-A- 5098347, US-A- 5152721, US-A- 5141475 and US-A- 5045031. In these disclosures, the tensioners have a suitable axial length or depth for some automotive camshaft drive configurations, but their design introduces some geometric problems that may prevent them from being used in other applications. In both of the tensioners, the pulley is recessed in the tensioner structure to an extent that it is at least partially surrounded by projections of the tensioner's structure. Such projections must be avoided by a belt as it is entrained around the tensioner pulley and other pulleys of the belt drives. The projections may substantially limit the applications for such tensioners because of space limitations of an automotive engine. Summary of the Invention In accordance with the invention as defined in claim 1, a tensioner is provided that is useful in conjunction with belt drive systems and is particularly useful in a toothed belt or synchronous belt drive system such as an automotive camshaft drive. Such belt drives are often referred to as timing belt drives. The belt tensioner of the invention is of the pivot type with a pivot arm pivotably mounted with a pivot to a base structure, and a pulley rotatably mounted to the pivot arm for engaging a belt. The pulley has generally a "tube-pan" configuration where it is open on an axial side to an annular space. A portion of the pivot protrudes into the annular space. A compression spring is interpositioned between a base structure and the pivot arm in such a manner to bias movement of the pivot arm. In accordance with the invention, part of the base structure and part of the pivot arm protrude into the annular space and the compression spring is interpositioned between such portions. At least part of a compression spring is also disposed in the annular space which gives the pulley a low or shallow axial profile in comparison to prior art tensioners. An advantage of the invention is that the pulley is not recessed relative to other component parts of the tensioner. Another advantage of the invention is that the pulley substantially encases a portion of the spring and pivot to effect a shallow tensioner profile while also providing shielding. Another advantage of the invention over prior art eccentric type tensioners is that a relatively smaller diameter and therefore economical bearing may be used (in comparison to eccentric type tensioners) while also obtaining a substantially longer pivot arm. An object of the invention is to locate at least a portion of the compression spring in the annular space of the pulley such that the spring is positioned generally chordally relative to the pulley. These and other objects or advantages of the invention will be apparent after reviewing the drawings and description thereof wherein: Fig. 1 is a schematic front view of a drive system that includes a belt entrained around pulleys and a tensioner of the invention; Fig. 2 is a view taken along the line 2-2 of Fig. 1 showing a side view of the tensioner excluding the belt; Fig. 3 is an enlarged cross-sectional view taken along the line 3-3 of Fig. 4; Fig. 4 is a cross-sectional view taken along the line 4-4 of Fig. 3; Fig. 5 is a partial cross-sectional view taken along the line 5-5 of Fig. 3 and further includes a superimposed partial cross-section of a pulley to show relative positioning of elements. Description of Preferred Embodiments While various features of the tensioner and belt drive system are best described in conjunction with a synchronous belt drive (timing belt drive) for an automotive engine, features of the invention may also be used in other belt tensioning applications such as for automotive front-end accessory drives. Referring to Fig. 1, a synchronous belt drive system 10 is shown with a toothed belt 12 entrained and tensioned around toothed pulleys. The illustrated drive system is a camshaft drive of the automotive type that includes at least one toothed cam pulley 14, a crank pulley 16 and a tensioning pulley 18 of a tensioner 20 of the invention. The tensioner may be held in position by means of fasteners such as cap screws 22 which fasten the tensioner to an engine 24 (only partially shown). As best shown in Fig. 2, the tensioner has a shallow axial depth or length and the pulley need not be recessed within other structural component parts of the tensioner. The tensioner design permits substantially 360 degrees access to the pulley which offers a variety of opportunities for designing various means for attaching the tensioner to an engine without creating obstructions that would interfere with a power transmission belt. Referring to Figs. 3-5, the belt tensioner 20 is of the spring bias type and includes a base structure 26 that may optionally include ears 28, 30 as a means for attaching the tensioner, a pivot arm 32 and a spring 34 biased between the base structure and pivot arm. The pivot arm 32 is pivotably mounted to the base structure by means of a pivot 36 and an optional, self-lubricating polymeric sleeve-type bearing or bushing 38 that may include a thrust cap or bearing 40. The pulley 18 is rotatably mounted to the pivot arm such as by means of a ball bearing 42. The pulley has generally a "tube-pan" configuration that opens on an axial side to an annular space 44. The base structure has a portion such as a post 46 that protrudes into the annular space and defines a means such as a boss 48 with a slot 50 for receiving an end of the spring 34 that includes a diametrically oriented tab. The pivot arm has a lever arm LV with a portion 52 that protrudes into the annular space 44 and includes a means such as a boss 54 with a slot 56 for receiving an end portion of the spring 34. The spring is a compression spring that is sized to at least partially, and more preferably substantially fit in the annular space. The spring is interpositioned between the post 46 of the base structure and portion of the pivot arm such that it is oriented substantially chordally relative to the pulley and is interconnected between the spring mounting means 48, 54. The spring is mounted to the base structure and pivot arm so that the spring articulates with movements of the pivot arm 32 and the moment arm LV varies in length with articulated movements of the spring in a manner as described in US-A-5045031. The moment arm shortens with a shortening of length of the compression spring and lengthens with a lengthening of the compression spring as the pivot arm is pivoted. A damping system or means 58 is included for inhibiting movement of the pivot arm 32 and hence the pulley against the belt when the tensioner is in use. The damping means 58 includes a leg or lever extension 60 providing a damping portion of the pivot arm 32, a damping spring 62, a portion 64 of the base structure, and two pads of friction material 66, 68. The second pad of friction material 68 is optional. The pivot arm 32 and base portion 64 are cupped to clear the pulley and are nested together juxtaposed each other in the annular space 44. A portion 70 of the pivot arm 32 protrudes into the annular space 44 and preferably has a planar surface portion 72. Similarly, the base portion 64 has planar surface portions 74, 76 that engage flat or planar surfaces of the pad(s) of friction material 66, 68. Each pad of friction material 66, 68 is preferably in the form of a washer which is sandwiched between a planar surface of the portion 70 and the portion 64. A pin type fastener such as a threaded bolt 78 extends through a slot or elongated aperture 80 of the base portion 74 and fastens to the pivot arm portion 70. The bolt 78 retains one end of the spring and is carried by the pivot arm as it arcuately moves about the pivot 36. The fastener 78 also functions to retain the pivot arm 32 to the base structure 26. The or each pad of friction material 66, 68 may be oblong in shape or circular to provide a sufficiently large surface for damping to take place by friction surface sliding. The friction material may be of any chosen type but it optionally may be in the form of a polymeric material such as nylon that sold under the trade mark DELRIN which exhibits a starting (static) friction that is less than its sliding (dynamic) friction. The convenience, the base structure of Figs. 4 and 5 are shown in vertical alignment so that the relative positioning of the compression spring 34, bearing 42 and damping means 58 may be seen to be preferably aligned with each other in a substantially constant plane. Such alignment minimizes forces which must be carried by the parts as it eliminates loads that could be introduced by couples due to offsetting of the components. To illustrate the compactness of the tensioner of the invention, a tensioner was constructed with a pulley having a diameter of 104mm and an axial face width of 36mm. Yet the tensioner had a total axial length of only 56mm. The short axial length was possible by using a compression spring having a diameter of 19mm and a nominal compressed length of 32mm. The spring was chordally fitted within the annular space of the generally tube-pan shaped pulley. Thus, the ratio of the tensioner axial length to pulley diameter is only .54. When installed in a belt drive system, the tensioner operates to maintain a tension of 36.29kg (801b) within a design tolerance of plus or minus 10 per cent. It will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Claims: A tensioner for tensioning a flexible power transmission member (12) and of the type with a base structure (26), a pivot arm (32) pivotably mounted with a pivot (36) to the base structure (26), pulley means (18) rotatably mounted to the pivot arm (32) for engaging the power transmission member (12) and having a generally tube-pan configuration that opens on an axial side to an annular space (44), a portion of the pivot (36) protruding into the annular space (44), a spring means (34) between the base structure (26) and pivot arm (32) for biasing the pivot arm (32), and means (58) for damping movement of the pivot arm, characterised in that the pivot arm (32) has a first lever arm (LV) with a portion (52) that protrudes into the annular space (44) and defines a first means (54,56) for connecting the spring means (34), the base structure (26) has a portion (46) that protrudes into the annular space (44) and defines a second means (48, 50) for connecting the spring means (34), and in that the spring means (34) is a compression spring (34) oriented substantially chordally relative to the pulley (18) and at least partially disposed in the annular space (44) and interconnected between the first (54,56) and second connecting means (48,50). The tensioner as claimed in claim 1, wherein the spring (34) is disposed in the annular space (44). The tensioner as claimed in claim 1 or 2, wherein the means (58) for damping movement of the pivot arm is characterised in that the pivot arm (32) has a second lever arm (60) with a damping portion (70) having a substantially planar surface portion (72) that protrudes into the annular space (44), the base structure (26) has a damping portion (64) with at least one substantially planar surface portion (76) that protrudes into the annular space (44) juxtaposed the pivot arm damping portion (70), a layer of friction material (66) is interpositioned between the pivot arm damping portion (70) and the base structure damping portion (64), and spring means (62) is provided for biasing the pivot arm damping portion (70), the base structure damping portion (64) and the friction material (66) into contact with each other to effect damping. The tensioner as claimed in claim 3, wherein the base structure damping portion (64) has a slotted aperture (80) therein, the layer of friction material (64) has an aperture aligned with the slotted aperture (80), the pivot arm damping portion (70) has a substantially planar surface (72) and wherein a pin (78) extends through the slotted aperture (80) and aperture in the layer of friction material (66), and wherein a compression spring (62) is positioned around and retained by the pin (78) and biases the pivot arm damping portion (70), the layer of friction material (66) and the base structure damping portion (64) against each other.

Inventors: DEC ANDRZEJ, THOMEY HENRY W, DEC, ANDRZEJ, THOMEY, HENRY W.
Applicants: GATES POWER DRIVE PROD INC, GATES POWER DRIVE PRODUCTS, INC.
Application year: 1991
Main classification: F16H7
IPC codes: F16H7