CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/736,793 filed December 13, 2012, the contents of which are incorporated herein in their entirety.

FIELD

[0002] This disclosure relates generally to the field of tensioners for an endless drive system, and more particularly to a tensioner for a timing belt system for a vehicle.

BACKGROUND

[0003] Tensioners are known for use in tensioning belts and the like that are driven by an engine in a vehicle. In general, tensioners for timing belts are relatively tall, however. As a result, a manufacturer that wants to revise the design of an engine with a chain drive to instead use a timing belt is in some instances unable to do so because there is too much added length to the engine assembly caused by the timing belt tensioner. It would be advantageous to provide a tensioner that can be used for timing belts (or other endless drive members) that has a reduced height. SUMMARY

[0004] In an aspect, a tensioner is provided for an endless drive member of a motor vehicle engine. The tensioner includes a pivot shaft having a basal end and a distal end, and defining a pivot shaft axis. The pivot shaft has a pivot shaft aperture therethrough. A tensioner arm is pivotally mounted on the pivot shaft for pivotal movement about the pivot shaft axis. A bearing is provided and has an inner surface mounted to the tensioner arm and having an outer surface. A pulley is mounted to the outer surface of the bearing so as to be rotatably supported on the tensioner arm for engaging the endless drive member. The pulley defines a pulley axis that is spaced from and generally parallel to the pivot shaft axis. A spring is positioned to urge the tensioner arm in a take-up direction. The bearing is closer to the basal end of the pivot shaft than is the spring. An installation shaft includes a guide portion that is rotatable within the pivot shaft aperture, and a head portion that engages the pivot shaft at least indirectly to hold the pivot shaft axially in place. The installation shaft has a fastener aperture for receiving a fastener for affixing the installation shaft and the pivot shaft axially and rotationally to a stationary structure. The fastener aperture defines a fastener axis that is offset from the pivot shaft axis.

[0005] Optionally the installation shaft has a recessed shoulder positioned for receiving a head of the fastener.

[0006] Optionally, the pivot shaft includes a head portion which contains a recessed distal-facing surface; the head portion of the installation shaft engages the distal-facing surface at least indirectly to hold the pivot shaft axially in place; and the head portion of the pivot shaft is in surrounding relationship to the head portion of the installation shaft such that the head portion of the installation shaft is at least partially recessed within the head portion of the pivot shaft.

[0007] Optionally, a top plate is provided that covers the spring; the top plate has a recess with a recessed shoulder, and is engaged with the pivot shaft; and the head portion of the installation shaft is at least partially recessed in the recess and holds the pivot shaft axially in place through engagement with the recessed shoulder of the top plate.

[0008] Optionally, the installation shaft has first and second tool-receiving apertures that are positioned to receive first and second tool ends to rotate the installation shaft about the pivot shaft axis; and the first and second tool receiving apertures are open channels along a radially outer face of the installation shaft.

BRIEF DESCRIPTION OF DRAWINGS

[0009] The foregoing and other aspects will be more readily appreciated having regard to the accompanying drawings, wherein:

[0010] Figure 1 is a plan view of an engine with an endless drive and a tensioner in accordance with an embodiment of the present invention;

[0011] Figure 2 is a perspective view of the tensioner shown in Figure 1 ;

[0012] Figure 3 is an exploded perspective view of the tensioner shown in Figure 1 ; [0013] Figure 4 is a sectional side view of the tensioner shown in Figure 1 ;

[0014] Figure 5 is another sectional side view of the tensioner shown in Figure 1 in comparison to a prior art tensioner;

[0015] Figure 6 is another sectional side view of the tensioner shown in Figure 1 showing an optional damping member;

[0016] Figure 7 is a sectional view of a variant of the tensioner shown in Figure 2; and

[0017] Figure 8 is another sectional side view of the variant shown in Figure 7, showing an optional damping member.

DETAILED DESCRIPTION OF EMBODIMENTS

[0018] Figure 1 is a plan view of an embodiment of a tensioner 10 usable for tensioning an endless drive member 11 that is part of an endless drive on a vehicle engine 913. The engine 913 is shown as a simple rectangle for illustrative purposes. It will be understood that the engine 913 may have any suitable shape.

[0019] The endless drive may use a pulley 912 on a crankshaft of the engine 913 to drive at least one component via the endless drive member 11. In the example shown a cam shaft pulley 916 is the component driven via the endless drive member 11. An idler 918 is also shown in engagement with the belt 11

[0020] The endless drive member 11 may be a timing belt, or it may be any other suitable type of endless drive member. [0021] Reference is made to Figures 2, 3 and 4 which show the tensioner 10 in greater detail. The tensioner 10 includes a pivot shaft 12, a base plate 13, a tensioner arm 14, a bushing 16, a bearing 18, a pulley 20, a tensioning spring 22, an installation shaft 24, a top plate 26 and a mounting fastener 28. The pivot shaft 12 is mountable to a stationary structure such as a first region on the frame or block of the engine 913 (Figure 4). For greater clarity, the stationary structure is the entirety of all suitable structural portions of the vehicle (or of the tensioner's environment in the case of a non-vehicular application) that is considered stationary for the purposes of mounting portions of the tensioner 10. In a vehicular application, this would correspond to the frame of the vehicle, the engine block and engine support frame, the vehicle body and any non-moving structural elements and components.

[0022] The pivot shaft 12 has a basal end 30 (i.e. an end that is proximate the stationary structure to which the pivot shaft 12 is mounted) and a distal end 32 and defines a pivot shaft axis Aps (Figure 4). The base plate 13 is fixedly mounted to the basal end 30 of the pivot shaft 12 (e.g. by press-fit, staking, welding, glue or any other suitable means). The pivot shaft 12 has a pivot shaft aperture 34 therethrough in which the installation shaft 24 is positioned. The pivot shaft 12 has a recessed shoulder which provides a distal-facing surface 36, that is described further below.

[0023] The top plate 26 is fixedly connected to the pivot shaft 12 and covers the spring 22. In the embodiment shown, the top plate 26 rests on a shoulder 37 at the distal end 32 of the pivot shaft 12. The top plate 26 may be press-fit onto the shoulder 37 in some embodiments or may be fixedly connected to the pivot shaft 12 in any other way.

[0024] The tensioner arm 14 is pivotally mounted on the pivot shaft 12 for pivotal movement about the pivot shaft axis Aps.

[0025] The tensioner arm 14 has the bushing 16 on its radially inner surface to permit pivotal movement relative to the pivot shaft 12. Optionally, in some embodiments (such as the embodiment shown in Figure 5) a disc bushing 17 may be provided between the tensioner arm 14 and the base plate 13 to control the frictional engagement therebetween. The bushings 16 and 17 may be made from any suitable material such as DU.

[0026] The bearing 18 has an inner surface 38 and an outer surface 40. The bearing 18 is mounted via its inner surface 38 to the tensioner arm 14. In the embodiment shown the bearing 18 is a single-row ball bearing, having an inner race 18a (which has the inner surface 38 thereon), an outer race 18b (which has the outer surface 40 thereon) and a plurality of balls 18c. While this is advantageous in that it provides a low axial height, other types of bearing may alternatively be used.

[0027] The pulley 20 is mounted to the outer surface 40 of the bearing 18 so as to be rotatably supported on the tensioner arm 14 for engaging the endless drive member 1 1 (Figure 1). The pulley 20 defines a pulley axis Ap that is spaced from and extends generally parallel to the pivot shaft axis Aps. The pulley 20 may lack flanges as shown in Figures 2-4 and 6, or it may have flanges as shown in Figures 5, 7 and 8.

[0028] The tensioning spring 22 is positioned to urge the tensioner arm 14 in a take-up direction, which drives the arm 14 and pulley 20 into the belt 11. The tensioning spring 22 may be any suitable type of spring, such as, for example, a helical coil torsion spring. The spring 22 is shown as being made from a wire having a rectangular cross-sectional shape, however, it may have any other suitable cross-sectional shape such as a circular cross-sectional shape. For the purposes of this disclosure, the term 'rectangular' is to include shapes having four sides that are dimensionally equal, and a shape having four sides where two of the sides are longer than the other two sides. Put another way, the spring 22 may be made from a wire having a cross-sectional shape that is rectangular, having an axial dimension and a radial dimension, wherein the radial dimension is at least as large as the axial dimension. In other words, in embodiments wherein two of the sides of the cross-sectional shape are longer, the longer sides are the radial sides and the shorter sides are the axial sides.

[0029] Referring to Figure 4, the spring 22 is positioned in a chamber 43 that is defined between the top plate 26 and the tensioner arm 14. As shown in Figures 2, 4 and 6, the spring 22 has a first end 44 that is engaged with a drive surface (in this instance, a surface of a slot 46) in the top plate 26. As a result of the fixed connection between the top plate 26 and the pivot shaft 12, the first end 44 is operatively engaged with the pivot shaft 12. It will be noted that only a small segment of the spring 22 proximate the end 44 is shown in Figure 2 for simplicity. With reference to Figure 3, the spring 22 has a second end 48 that is engaged with a drive surface (in this instance a surface of a slot 50) in the tensioner arm 14. Thus, the second end 48 is operatively engaged with the tensionser arm 14.

[0030] In addition to urging the arm 14 in the take-up direction, the spring 22 may be in an axially compressed state in the chamber 43, and as a result it exerts an axial force on the tensioner arm 14 to keep the arm 14 axially fixed in position. In the embodiment shown, the axial position of the arm 14 is in engagement with the base plate 13. In such embodiments, the base plate 13 may have a coating thereon to reduce wear on it and/or on the arm 14 during pivotal movement of the arm 14.

[0031] During engagement of the pulley 20 with the belt 11 (Figure 1) the tensioner arm 14 is in a state of flexure and therefore applies a tensioning force on the belt 11 via the arm 14 and pulley 20. During events where the belt tension increases, the arm 14 is rotated in a load stop direction (counterclockwise in the view shown in Figure 2), which increases the amount of flexure of the spring 22 and which therefore increases the biasing force of the spring 22 on the arm 14 in the take-up direction (clockwise in the view shown in Figure 2).

[0032] The installation shaft 24 is rotatably mounted within the pivot shaft 12 (by way of a guide portion 51 that extends within the pivot shaft aperture 34), and is rotatable about the pivot shaft axis Aps. The installation shaft 24 has a fastener aperture 52 for receiving the fastener 28 for affixing the pivot shaft 12 to the stationary structure 913, and for preventing relative rotational movement between the installation shaft 24 and the pivot shaft 12. The fastener aperture 52 defines a fastener axis (shown in Figure 4 by axis Af) that is offset from the pivot shaft axis Aps. As a result, prior to tightening down the fastener 28, the installation shaft 24 can be pivoted about the fastener axis Af so as to permit adjustment of the position of the pivot shaft 12 and therefore the pivot shaft axis Aps, which is the pivot axis for the tensioner arm 14. Then, once the fastener 28 is tightened down fully, the installation shaft 24 is fixed in position along with the pivot shaft 12, thereby fixing the position of the pivot shaft axis Aps. To fix the position of the installation shaft 24 and the pivot shaft 12 with the fastener 28, the fastener 28 bears upon the installation shaft 24, and the installation shaft 24 in turn bears upon the pivot shaft 12. More specifically, the fastener 28 has a head portion 56 that bears on a shoulder 54 on the installation shaft 24 and further includes a body portion 58 that passes through the fastener aperture 52 and engages (e.g. by threaded engagement) a mounting aperture in the stationary structure 913. The installation shaft 24 in turn has a head portion 60 that at least indirectly bears upon the distal- facing surface 36 so that upon tightening of the fastener 28, both the installation shaft 24 and the pivot shaft 12 are fixed rotationally and axially to the stationary structure 913. In the example shown in Figure 4, the head portion 60 bears directly on the surface 36. In the example shown in Figure 7, the head portion 60 bears indirectly on the surface 36 through engagement with a shoulder on the top plate 26, which is described further below. [0033] The tensioner arm 14 remains pivotably movable on the pivot shaft after tightening of the fastener 28 so that the arm 14 can respond (by the urging of the spring 22) to changes in tension in the belt 11.

[0034] The fastener 28 may be a socket head bolt or any other suitable type of fastener. Preferably the fastener is a threaded fastener for engaging a threaded aperture in the stationary structure.

[0035] A feature of the tensioner 10 is that that the bearing 18 is closer than the spring 22 to the basal end 30 of the pivot shaft 12. This is an opposite arrangement to some timing belt tensioners which have the spring positioned closer to the basal end than is the bearing. By positioning the spring 22 towards the distal end 32 of the pivot shaft, there is room to recess the head portion 60 of the installation shaft 24 into the region in the middle of the spring 18, which is wider than the inner diameter of the bearing 18. Furthermore, the head portion 60 of the installation shaft 24 is sufficiently large that the shoulder 54 on the installation shaft 24 against which the fastener 28 bears may itself be recessed into the installation shaft 24, as shown in Figure 4. The shoulder 54 may be sufficiently recessed that the head 56 of the fastener 28 does not extend farther distally than a distal surface (shown at 62) of the installation shaft 24. In other words, the head 56 of the fastener 28 is completely sunken in a fastener head-receiving portion 64 of the fastener aperture 54.

[0036] With these advantageous features, it has been found that some examples of the tensioner 10 may be 25mm tall, (i.e. 25mm axially from the mounting surface on which the tensioner 10 is mounted). Some examples of the tensioner 10 may be even shorter axially. Its compact size lends itself to certain applications. For example, in some cases a vehicle manufacturer wants the freedom to use a timing chain drive for the camshafts of an engine, but wants to retain the flexibility of turning to a belt-in-oil design if desired, with relatively little redesign of the engine. By using the tensioner 10, a belt-in-oil system can replace a chain drive system while fitting inside the timing chain cover, eliminating the need for a costly redesign of the cover. Using a typical tensioner shown at 800 in Figure 5 however, there may not be enough room to fit such a tensioner in the interior of the timing chain cover, while still permitting the engine to fit within the space allotted for it underhood in a vehicle.

[0037] Figure 5 shows both the tensioner 10 and the prior art tensioner 800 aligned on a common reference plane P (e.g. as if mounted to the same engine block) to illustrate the differences in their relative axial heights. Both tensioners 10 and 800 are shown as the same scale.

[0038] The tensioner 10 may further include a damping element 70, shown in the partial sectional view in Figure 6. The damping element 70 may be fixed rotationally to the top plate 26 (and therefore to the pivot shaft 12), by way of projections 72 on the damping element that engage apertures 74 in the top plate 26. During operation of the tensioner 10, frictional damping takes place between the radially inner surface (shown at 76) of the damping member 70 and the tensioner arm 14 as the tensioner arm 14 moves relative to the damping member 70. Furthermore, as the tensioner arm 14 moves and increases the amount of flexure in the spring 22, the coils of the spring 22 constrict to urge the damping member 70 into increased frictional engagement with the arm 14. Thus the damping force varies with the position of the arm 14.

[0039] In some embodiments, the damping member 70 may be collapsible radially so as to permit a greater amount of frictional contact with the tensioner arm 14 than a damping member that is not collapsible radially. To provide collapsibility, the damping member 70 may be generally C-shaped, or it may have a construction that is similar to the damping structure described in PCT publication no WO2013/059929, the contents of which are incorporated herein in their entirety.

[0040] Referring to Figure 2, the installation shaft 24 includes two tool- receiving apertures 94a and 94b which are spaced from each other on the distal surface 62 of the installation shaft 24. The tool-receiving apertures 94a and 94b are positioned to receive ends 96a and 96b of a tool 96 that can be used to apply a torque to the installation shaft 24 to adjust the rotational position thereof. It can be seen that the apertures 94a and 94b are positioned at the peripheral edge of the installation shaft 24 such that they are open channels that extend axially on a radially outer face 97 (best seen in Figure 3) of the installation shaft 24. In the embodiment shown they are defined in part by the installation shaft 24 and in part by the pivot shaft 12. This permits them to be spaced as far apart as possible so as to provide as much room as possible to situate the recess 64 for the head 56 of the fastener 28. [0041] The pivot shaft 12 for the tensioner 0 shown in Figures 2-6 includes a head portion shown at 80, which contains a recessed shoulder which is the distal-facing surface 36. The head portion 80 is in surrounding relationship to the head portion 60 of the installation shaft 24 such that the head portion 60 of the installation shaft 24 is at least partially recessed within the head portion 80 of the pivot shaft 12. In the embodiment shown, the head portion 60 is fully recessed within the head portion 80.

[0042] Reference is made to Figure 7 which shows a variant of the tensioner shown in Figures 2-6. A difference between the tensioner 10 shown in Figure 7 and the tensioner 10 in Figures 2-6 is that the pivot shaft 12 in Figure 7 no longer has the head portion 80. Instead, the top plate 26 includes a recess 82 which includes a circumferential wall 84 and a radial wall 86. The radial wall 86 sits on the distal-facing surface 36 of the pivot shaft 12 and is press-fit (or rotationally fixedly mounted in any other suitable way) onto the radially outer surface of the pivot shaft 12. The radial wall 86 also provides a recessed shoulder 88 on which the head portion 60 of the installation shaft 24 rests and transfers the axial clamping force of the fastener 28 to the pivot shaft 12. Thus, in this embodiment, the head portion 60 of the installation shaft 24 holds the pivot shaft 12 axially in place, through engagement with the recessed shoulder 88 of the top plate 26. As can be seen in Figure 7, the head portion 60 of the installation shaft 24 is at least partially recessed in the recess 82 and holds the pivot shaft 12 axially in place through engagement with the recessed shoulder 88 of the top plate 26. [0043] The embodiment shown in Figure 7 may also include a damping member 70, as shown in Figure 8. The damping member 70 in this embodiment includes one or more projections 90 which engage apertures 92 in the tensioner arm 14 so that the damping member 70 is rotationally fixed to the tensioner arm 14. A radially inner surface 76 of the damping member 70 frictionally engages an engagement surface on the circumferential wall 84 of the top plate 26 which is stationary during operation of the tensioner 10, thereby providing a damping force during pivotal movement of the tensioner arm 14. As in the embodiment shown in Figure 6, the damping force may be based on the amount of tensioning force (and therefore the degree of constriction) that is present in the spring 22, thereby making the damping force vary based on arm position.

[0044] Embodiments have been described wherein the tensioner has two features, namely a first feature, which is an installation shaft that has a head that is recessed at least partially into a recess in the top plate or into a head portion in the pivot shaft, and a second feature, which is that the installation shaft also includes a recess itself for receiving the head of the fastener. It will be noted that some embodiments of the invention may have either one of these two features independent of whether it has the other.

[0045] Those skilled in the art will appreciate that a variety of modifications may be made to the embodiments described herein without departing from the fair meaning of the accompanying claims.