CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62/075,595 filed November 05, 2014, the contents of which are incorporated herein in their entirety.

FIELD

[0002] This disclosure relates to tensioners and in particular tensioners that operate to tension synchronous endless drive members such as a timing belt on an engine.

BACKGROUND

[0003] Tensioners are known devices for maintaining tension in belts (e.g. timing belts) or other endless drive members that are driven by an engine and that are used to drive certain components, such as camshafts. A tensioner typically includes a base that mounts to the engine, a tensioner arm that is pivotable with respect to the base about a pivot axis, a pulley that is mounted at a free end of the arm for engagement with the belt, and a spring that acts between the base and the arm to drive the arm into the belt. The direction into the belt (i.e. the direction in which the spring drives the arm) may be referred to as a direction towards a free arm position (i.e. towards a position that the tensioner arm would reach if no belt were present to stop it). This is a direction of lessening spring potential energy. The tensioner arm in general moves in this direction as the belt tension drops. The direction away from the belt (i.e. the direction against the biasing force of the spring) may be referred to as a direction towards a load stop position, and is a direction of increasing spring potential energy. The tensioner arm in general moves in this direction as the belt tension increases. It is generally desirable to prevent abrupt limiting of the movement of the arm in the load stop direction, so as to reduce sudden increases in stress in the components of the tensioner. SUMMARY

[0004] In an aspect, a tensioner for an endless drive member is provided, and includes a shaft and base unit, a tensioner arm, a pulley, a tensioner spring and a sleeve. The shaft and base unit is mountable to be stationary relative to an engine. The tensioner arm is pivotably mounted on the shaft and base unit for pivoting movement about an arm pivot axis. The pulley is rotatable on the tensioner arm about a pulley axis that is offset from the arm pivot axis. The pulley is engageable with an endless drive member. The tensioner spring is a helical torsion spring and is positioned to urge the tensioner arm in a free arm direction. The tensioner arm is urgable by the endless drive member in a load stop direction that is opposed to the free arm direction against urging by the tensioner spring. Movement of the tensioner arm in the load stop direction causes a dimension change in the tensioner spring in a first radial direction. The sleeve is fixed to one of the tensioner arm and the shaft and base unit and is radially engageable with the tensioner spring to limit dimensional change of the tensioner spring in the first radial direction. The sleeve has a plurality of axially extending ribs extending about a perimeter of the sleeve, which are circumferentially spaced from one another and which are all simultaneously progressively engageable with the tensioner spring between a first angular position and a second angular position at which the tensioner spring is prevented from further movement in the first radial direction, thereby preventing movement of the tensioner arm beyond the second angular position.

BRIEF DESCRIPTION OF THE DRAWINGS [0005] Figure 1 is a side view of an engine with a tensioner in accordance with an embodiment of the present invention; [0006] Figure 2 is an exploded perspective view of the tensioner shown in Figure

1 ;

[0007] Figure 3 is a sectional perspective view of the tensioner shown in Figure

1 ; [0008] Figure 4 is an upside down sectional perspective view of a sleeve that is part of the tensioner shown in Figure 1 ;

[0009] Figure 5 is a magnified sectional perspective view of a portion of the tensioner shown in Figure 1 ;

[0010] Figures 6a and 6b are sectional plan views a portion of the tensioner shown in Figure 1 , showing a tensioner arm in a first angular position and a second angular position respectively;

[0011] Figure 7 is a graph showing a tension/position curve for a prior art tensioner; and

[0012] Figure 8 is a graph showing a tension/position curve for the tensioner shown in Figure 1.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0013] A timing drive 10 for an engine 101 is shown in Figure 1 . The timing drive 10 includes a tensioner 100 in accordance with an embodiment of the present disclosure. The tensioner 100 is mounted to a stationary member such as the block of the engine 101 and is engaged with an endless drive member 103, which may be, for example, a timing belt, a timing chain, or any other suitable synchronous endless drive member. The endless drive member 103 transfers rotational power from a crankshaft 104 to a pair of camshafts 105a and 105b. [0014] An exploded view of the tensioner 100 is shown in Figure 2. The tensioner 100 includes a shaft and base unit 1 13, a tensioner arm 1 19, a tensioner pulley 120 and a tensioner spring 122. The shaft and base unit 1 13 is mountable to be stationary relative to the engine 101 and defines an arm pivot axis AA (Figure 3) for the tensioner arm 1 19. The shaft and base unit 1 13 includes a shaft 1 14 and a base 115 and may optionally further include an installation eccentric member 1 1 1 that is mountable in a mounting aperture 1 12 of the shaft 1 14 and cooperates with the wall 1 12a (Figure 3) of the mounting aperture 1 12 of the shaft 114 to define a fastener pass- through aperture 1 16 for receiving a tensioner mounting fastener 117. The base 115 may be fixedly mounted to the shaft 1 14 (e.g. by staking or any other suitable means). The tensioner mounting fastener 1 17 passes through the aperture 1 16 and threads into a receiving aperture 101 a in the block of the engine 101 to fixedly mount the shaft and base unit 1 13 thereto. A first rotational locking feature 1 15a (e.g. an axial projection) of the shaft and base unit 1 13 (shown in Figure 3 on the base 1 15) may engage snuggly into a second rotational locking feature (e.g. an axial receiving aperture 101 b on the block of the engine 101 to rotationally lock the shaft and base unit 1 13 when it is mounted to the engine 101.

[0015] The installation eccentric member 1 1 1 is movable over a range of rotational positions in the mounting aperture 112. Movement of the installation eccentric member 1 1 1 to different rotational positions within the mounting aperture 1 12 moves the outer surface 1 14a of the shaft 1 14 relative to the receiving aperture 1 18 on the engine 101 , thereby providing some adjustment to the position of the tensioner arm 1 19. In some embodiments, the installation eccentric member 11 1 may be omitted in which case the base 1 15 may be mounted (e.g. by staking) to the shaft 1 14. [0016] The tensioner arm 1 19 is pivotably mounted on the shaft 1 14 for pivoting movement about the arm pivot axis AA. A bushing 123 may be provided between the tensioner arm 1 19 and the outer surface 1 14a of the shaft 114 to control the amount of friction present pivoting of the tensioner arm 1 19. The bushing 123 may be made from any suitable material such as a suitable nylon and may optionally be impregnated with a material such as Teflon™.

[0017] The pulley 120 is rotatably mounted to the tensioner arm 1 19 (e.g. by means of a ball bearing 121 ) for rotation about a pulley axis AP (Figure 3) that is offset from the arm pivot axis AA. The pulley 120 is engageable with the endless drive member 103 (Figure 1 ).

[0018] A thrust member 125 may be provided and axially supports the components of the tensioner 100 at a distal end of the shaft 1 14.

[0019] Referring to Figure 2, the shaft and base unit 1 13 (the base 1 15 in this particular example) includes a first spring end locking feature 126 (e.g. a slot) that receives and locks a first tang at the first end 128 of the tensioner spring 122 to the shaft and base unit 1 13. The tensioner arm 1 19 includes a second spring end locking feature 130 (e.g. a slot) that receives and locks a second tang at the second end 132 of the tensioner spring 122 to the tensioner arm 1 19. [0020] The tensioner spring 122 may be a helical torsion spring and is positioned to urge the tensioner arm 1 19 in a free arm direction FA (shown in Figure 2). The tensioner arm 1 19 is urgable by the endless drive member 101 (i.e. by engagement of the endless drive member 103 with the pulley 120) in a load stop direction LS (Figure 1 ) that is opposed to the free arm direction FA against urging by the tensioner spring 122. Movement of the tensioner arm 122 in the load stop direction LS causes a dimension change in the tensioner spring in a first radial direction RD1 (shown in Figure 5). In the example shown, the first radial direction RD1 is radially inwardly.

[0021] A sleeve 140 that is fixed to one of the tensioner arm 1 19 and the shaft and base unit 1 13 is used to progressively lock the tensioner spring 122 to limit movement of the tensioner arm 119 relative to the shaft and base unit 1 13. In the embodiment shown the sleeve 140 is fixed to the tensioner arm 119 (e.g. by means of an adhesive). The sleeve 140 is radially engageable with the tensioner spring 122 to limit dimensional change of the tensioner spring 122 in the first radial direction RD1 when the tensioner arm 1 19 is beyond a selected angular position relative to the shaft and base unit 1 13. In some embodiments, the sleeve 140 is configured to provide a gradual or progressive engagement with the tensioner spring 1 19 so that the amount of resistance to movement of the arm 1 19 increases progressively until the spring 1 19 is stopped from any further radial shrinkage, which stops the arm 1 19 from any further rotation in the load stop direction LS. In the embodiment shown, this progressive locking of the arm 1 19 is provided by a plurality of axially extending ribs 142, which are circumferentially spaced on the outer surface 144 (Figure 4) of the sleeve 140 in the example embodiment shown. In the example embodiment shown, there are six ribs 142 which are equally spaced about the perimeter of the sleeve 140, however, any other suitable number of ribs 142 and any other suitable (equal or unequal) spacing may be provided between them. The ribs 142 are all simultaneously progressively engageable with the tensioner spring 122 between a first angular position (shown at P1 in Figure 6a) and a second angular position shown at P2 in Figure 6a) at which the tensioner spring 1 19 is prevented from further movement in the first radial direction RD1 , thereby preventing movement of the tensioner arm 1 19 beyond the second angular position P2.

[0022] The progressive engagement provides effectively a progressive amount of interference between the outer diameter of the sleeve 140 at the ribs 142 and the inner diameter of the spring 122. The spaces between the ribs 142 permit the effective inner diameter of the spring 122 to decrease to a level that is smaller than the outer diameter of the sleeve 140 at the ribs 142. At the first angular position P1 , which may be, for example, about 70 degrees from a free arm position PFA of the tensioner arm 119 (Figure 6a), the ribs 142 all simultaneously engage the spring 122 and progressively engage the tensioner spring 122 between the first angular position P1 and the second angular position P2 at which the tensioner spring 122 is prevented from further movement in the first radial direction RD1 , thereby preventing movement of the tensioner arm 1 19 beyond the second angular position P2. The second angular position P2 may be, for example about 100 degrees from a free arm position PFA, thereby providing an angular range over which the progressive engagement occurs between the first and second positions of about 30 degrees. The effective amount of interference may be about 0mm of interference at the first angular position (about 70 degrees from position PFA), about 0.16mm of interference at a first intermediate position (e.g. about 80 degrees from position PFA), about 0.32mm of interference at a second intermediate position (e.g. about 90 degrees from position PFA), and about 0.5mm of interference at the second angular position.

[0023] The material of the sleeve 140 may be any suitable material such as a suitable nylon. The spring 122 may be any suitable material such as a suitable steel.

[0024] Figures 7 and 8 show an example tension/position curve 200 for a prior art tensioner (Figure 7) and an example tension/position curve 202 for the tensioner 100 (Figure 8). As can be seen towards the right of the curve 202, the tension builds up gradually and progressively once the arm 1 19 reaches the first angular position PL

[0025] The above-described embodiments are intended to be examples only, and alterations and modifications may be carried out to those embodiments by those of skill in the art.