CN110546405A

CN110546405A - Timing belt tensioner with improved structure

Info

Publication number: CN110546405A
Application number: CN201880027266.1A
Authority: CN
Inventors: 米洛斯·巴廖佐维奇; 拉雷什·I·科姆沙; 弗拉维乌·V·丁卡
Original assignee: Litens Automotive Partnership
Current assignee: Litens Automotive Partnership
Priority date: 2017-10-04
Filing date: 2018-05-01
Publication date: 2019-12-06
Anticipated expiration: 2038-05-01
Also published as: CN110546405B

Abstract

in one aspect, a tensioner for an endless drive member is provided and includes a shaft and base unit, a tensioner arm, a pulley, and a tensioner spring. The shaft and base unit are mountable to be fixed relative to the engine and include fastener apertures for fasteners. The tensioner arm is pivotable relative to the shaft and the base unit about a tensioner arm axis. A pulley is rotatably mounted to the tensioner arm for rotation and is engageable with the endless drive member. The tensioner spring is positioned to urge the tensioner arm in a first direction relative to the shaft and the base unit. The tensioner spring includes a plurality of coils arranged in a generally helical manner about a longitudinal axis and radially spaced from one another and generally increasing in distance from the axis in a longitudinal direction.

Description

timing belt tensioner with improved structure

This application claims priority to U.S. provisional patent application No.62/491,469 filed on day 28, 2017 and U.S. provisional patent application No.62/568,097 filed on day 4, 2017, both of which are incorporated herein in their entirety.

Technical Field

The present disclosure relates to tensioners, and in particular to tensioners that operate to tension a synchronous endless drive member, such as a timing belt on an engine.

Background

Tensioners are known devices for maintaining tension in a belt (e.g., a timing belt) or other endless drive member that is driven by an engine and used to drive a particular component such as a camshaft. The tensioner generally includes a shaft and base unit mounted to the engine, a tensioner arm pivotable about a pivot axis relative to the base, a pulley mounted to the arm for engagement with the belt, and a spring acting between the base and the arm to drive the arm into the belt. The direction of entry into the belt (i.e., the direction in which the spring drives the arm) may be referred to as the direction toward the free arm position (i.e., toward the position that the tensioner arm would reach without the belt stopping the tensioner arm). This is the direction of decreasing spring potential energy. The tensioner arm typically moves in this direction when the belt tension decreases. The direction away from the belt (i.e., the direction against the biasing force of the spring) may be referred to as the direction toward the load stop position, and is the direction in which the spring potential energy increases. The tensioner arm typically moves in this direction as the belt tension increases. It is known that it is desirable to provide damping on a tensioner to assist the tensioner arm against being thrown off the belt (e.g., a timing belt) during a sudden increase in belt tension that may cause the tensioner arm to suddenly accelerate toward a load stop position. However, in at least some applications, it would be beneficial to provide a tensioner that is improved (e.g., more compact) as compared to some other tensioners.

disclosure of Invention

in one aspect, a tensioner for an endless drive member is provided. The tensioner includes a shaft and base unit mountable in fixed relation to the engine, a tensioner arm, a pulley, a bushing, and a tensioner spring. The shaft and base unit includes fastener apertures to allow fasteners to pass through to fixedly connect the shaft and base unit to the engine. The tensioner arm is pivotable relative to the shaft and the base unit about an arm pivot axis. The tensioner arm has a first axial arm end and a second axial arm end. The tensioner arm has a radially outer surface that includes a pulley bearing surface and that extends from the first axial arm end to the second axial arm end without any radial protrusions at all. The pulley is rotatably supported on a pulley support surface of the tensioner arm for rotation about a pulley axis that is offset relative to the tensioner arm axis, wherein the pulley is engageable with the endless drive member. The bushing is positioned radially between the shaft and base unit and the tensioner arm to radially support the tensioner arm on the shaft and base unit. The tensioner spring is positioned to urge the tensioner arm in a first direction about the tensioner arm axis.

in another aspect, a tensioner for an endless drive member is provided and includes a shaft and base unit mountable to be fixed relative to an engine, a tensioner arm, a pulley, a bushing, a tensioner spring, and a damping carrier. The shaft and base unit includes fastener apertures to allow fasteners to pass through to fixedly connect the shaft and base unit to the engine. The tensioner arm is pivotable relative to the shaft and the base unit about a tensioner arm axis. The pulley is rotatably mounted to the tensioner arm for rotation about a pulley axis that is offset relative to the tensioner arm axis. The pulley is engageable with an endless drive member. A bushing is positioned radially between the shaft and base unit and the tensioner arm to radially support the tensioner arm on the shaft and base unit. The tensioner spring is positioned to urge the tensioner arm in a first direction about the tensioner arm axis. The tensioner spring is a torsion spring having a first end and a second end and a plurality of coils located between the first end and the second end. The first and second ends are urged by the shaft and base unit and the tensioner arm, respectively, during torque transmission between the first and second ends so as to radially expand the coil. The damping carrier includes a spring end engagement slot positioned to retain the second spring end. The damping carrier also includes a radially inner damping surface thereon. The second spring end and the radially inner damping surface are oriented relative to each other such that a tangential force from the tensioner arm on the tensioner spring at the second spring end results in a reaction force on the shaft and the base unit on the radially inner damping surface, thereby creating frictional damping during movement of the tensioner arm relative to the shaft and the base unit about the arm pivot axis.

In yet another aspect, a tensioner for an endless drive member is provided and includes a shaft and base unit, a tensioner arm, a pulley, and a tensioner spring. The shaft and base unit can be mounted stationary relative to the engine. The shaft and base unit includes fastener apertures to allow fasteners to pass through to fixedly connect the shaft and base unit to the engine. The tensioner arm is pivotable relative to the shaft and the base unit about a tensioner arm axis. The pulley has an annular drive member engagement surface engageable with the annular drive member. The pulley can be rotatably mounted to the tensioner arm for rotation about a pulley axis that is offset from the tensioner arm axis by an offset distance that is less than a radius of the pulley at the endless drive member engaging surface. The tensioner spring is positioned to urge the tensioner arm in a first direction relative to the shaft and the base unit. The tensioner spring includes a plurality of coils spaced apart from one another by a coil-to-coil gap. The spacing between any two adjacent coils of the plurality of coils to enter the tensioner spring is less than the width of each coil of the plurality of coils so as to prevent the tensioner spring from tangling with another identical tensioner spring.

In yet another aspect, a tensioner for an endless drive member is provided and includes a shaft and base unit, a tensioner arm, a pulley, and a tensioner spring. The shaft and base unit are mountable to be fixed relative to the engine and include fastener apertures to allow fasteners to pass therethrough to fixedly connect the shaft and base unit to the engine. The tensioner arm is pivotable relative to the shaft and the base unit about a tensioner arm axis. The pulley can be rotatably mounted to the tensioner arm for rotation about a pulley axis that is offset relative to the tensioner arm axis. The pulley is engageable with an endless drive member. The tensioner spring is positioned to urge the tensioner arm in a first direction relative to the shaft and the base unit. The tensioner spring includes a plurality of coils arranged in a generally helical manner about the longitudinal axis and radially spaced from one another and generally increasing in distance from the axis in the longitudinal direction.

in yet another aspect, a tensioner for an endless drive member is provided and includes a shaft and base unit, a tensioner arm, a pulley, and a tensioner spring. The shaft and base unit are mountable to be fixed relative to the engine and include fastener apertures to allow fasteners to pass therethrough to fixedly connect the shaft and base unit to the engine. The shaft and base unit includes a base and a shaft separate from the base and having the base mounted thereon. The shaft has an axis and has a first axial shaft end and a second axial shaft end. The shaft has a radially outer surface that includes the arm bearing surface and extends from the first axial shaft end to the second axial shaft end without any radial protrusions at all. The tensioner arm is pivotally supported on the arm support surface of the shaft for pivotal movement about a tensioner arm axis. A pulley is rotatably mounted to the tensioner arm for rotation about a pulley axis offset from the tensioner arm axis, wherein the pulley is engageable with the endless drive member. The tensioner spring is positioned to urge the tensioner arm in a first direction relative to the shaft and the base unit. The tensioner spring has a first end, a second end, and a plurality of coils between the first end and the second end. The first end is positioned to transmit torque with the base and the second end is positioned to transmit torque with the tensioner arm.

In yet another aspect, a tensioner for an endless drive member is provided and includes a shaft and base unit, a tensioner arm, a pulley, and a tensioner spring. The shaft and base unit are mountable to be fixed relative to the engine and include fastener apertures to allow fasteners to pass therethrough to fixedly connect the shaft and base unit to the engine. The shaft and base unit includes a base and a shaft separate from the base and having the base mounted thereon. The shaft has an axis and has a first axial shaft end and a second axial shaft end. The shaft has a radially outer surface that includes the arm bearing surface and extends from the first axial shaft end to the second axial shaft end without any radial protrusions at all. The tensioner arm is pivotally supported on the arm support surface of the shaft for pivotal movement about a tensioner arm axis. A pulley is rotatably mounted to the tensioner arm for rotation about a pulley axis offset from the tensioner arm axis, wherein the pulley is engageable with the endless drive member. The tensioner spring is positioned to urge the tensioner arm in a first direction relative to the shaft and the base unit. The tensioner spring includes a plurality of coils arranged about the longitudinal axis such that the coils are radially offset from each other and axially stacked on each other. The plurality of coils includes a radially outermost coil and at least one inner coil. The tensioner arm and at least one of the shaft and the base unit have spring limiting surfaces. As the tension in the endless drive member increases, the tensioner spring becomes progressively locked by the coils progressively expanding into engagement with each other and the radially outermost coils progressively expanding into engagement with the spring limiting surface.

in yet another aspect, a tensioner for an endless drive member is provided and includes a shaft and base unit, a tensioner arm, a pulley, and a tensioner spring. The shaft and base unit can be mounted stationary relative to the engine. The shaft and base unit includes fastener apertures to allow fasteners to pass through to fixedly connect the shaft and base unit to the engine. The tensioner arm is pivotable relative to the shaft and the base unit about a tensioner arm axis. A pulley is rotatably mounted to the tensioner arm for rotation about a pulley axis offset from the tensioner arm axis, wherein the pulley is engageable with the endless drive member. The tensioner spring is positioned to urge the tensioner arm in a first direction relative to the shaft and the base unit. The tensioner spring includes a plurality of coils arranged about the longitudinal axis such that the coils are radially offset from each other but axially stacked on each other. The plurality of coils includes a radially outermost coil and at least one inner coil. The tensioner arm and at least one of the shaft and the base unit have spring limiting surfaces. When the tension in the endless drive member increases to a selected tension, radial expansion of the plurality of coils is prevented by engagement of the plurality of coils with the at least one spring limiting surface.

in yet another aspect, a tensioner for an endless drive member is provided. The tensioner includes a shaft and base unit, a tensioner arm, a pulley, a tensioner spring, and a damping carrier. The shaft and base unit can be mounted stationary relative to the engine. The tensioner arm is pivotable relative to the shaft and the base unit about a tensioner arm axis. The pulley is rotatably mounted to the tensioner arm for rotation about a pulley axis that is offset relative to the tensioner arm axis. The pulley is engageable with an endless drive member. The tensioner spring is positioned to urge the tensioner arm in a first direction about the tensioner arm axis. The tensioner spring is positioned to urge the tensioner arm in a first direction about the tensioner arm axis. The tensioner spring is a torsion spring having first and second spring ends and a plurality of coils located between the first and second spring ends. The shaft and base unit are positioned to receive torque from the first spring end and the tensioner arm is positioned to receive torque from the second spring end. The damping carrier includes a spring end engagement slot that retains one of the first and second spring ends. The damping carrier also includes a first damping surface thereon. The first spring end, the second spring end and the first damping surface are positioned relative to each other such that the damping carrier pivots during force transfer between the tensioner arm and the shaft and base unit through the tensioner spring so as to drive the first damping surface into a complementary second damping surface on either of the tensioner arm and the shaft and base unit that receives torque from the other of the first spring end and the second spring end.

in yet another aspect, a method of assembling a shaft cover to a shaft for a tensioner is provided, the method comprising:

Providing a shaft having a cylindrical body, the shaft having a first axial shaft end and a second axial shaft end;

Providing a shaft cover;

Disposing a shaft cover over one of the first and second axial shaft ends, wherein the shaft cover has a plurality of staking apertures exposing the one of the first and second axial shaft ends, wherein the shaft cover further includes a staking shoulder positioned proximate to but spaced from the one of the first and second axial shaft ends toward the other of the first and second axial shaft ends;

inserting a staking protrusion into the staking aperture to engage the one of the first and second axial shaft ends; and

the one of the first and second axial shaft ends is deformed using the staking projection such that the one of the first and second axial shaft ends projects radially into the staking shoulder, thereby locking the shaft cap to the shaft.

In yet another aspect, a tensioner for an endless drive member is provided, the tensioner comprising: a shaft and base unit mountable to be fixed relative to an engine block; a tensioner arm pivotable about a tensioner arm axis relative to the shaft and the base unit; a pulley rotatably mounted to the tensioner arm for rotation about a pulley axis offset from the tensioner arm axis, wherein the pulley is engageable with an endless drive member, wherein the pulley has a swept volume; and a tensioner spring positioned to urge the tensioner arm in a first direction about a tensioner arm axis, wherein the tensioner spring is a torsion spring having a first spring end and a second spring end and a plurality of coils located between the first spring end and the second spring end, wherein a diameter of the plurality of coils decreases from one of the first spring end and the second spring end to the other of the first spring end and the second spring end, wherein one of the first spring end and the second spring end is positioned to transmit torque into the shaft and the base unit and the other of the first spring end and the second spring end is positioned to transmit torque into the tensioner arm, wherein the tensioner spring is positioned substantially entirely within a swept volume of the pulley.

Drawings

FIG. 1 is a front view of an engine having an endless drive arrangement including a tensioner according to an embodiment of the present disclosure including a first damping member and a second damping member;

FIG. 2 is an enlarged perspective view of the portion shown in FIG. 1;

FIGS. 3 and 4 are exploded perspective views of the tensioner shown in FIG. 1;

FIG. 5 is a side cross-sectional view of the tensioner shown in FIG. 1;

FIG. 6 is a side cross-sectional view of a spring that may be included in the tensioner shown in FIG. 1;

FIG. 7 is a perspective view of the spring shown in FIG. 6;

FIG. 8 is a prior art spring;

FIG. 9A is a perspective view of a shaft from a shaft and base unit that is part of the tensioner shown in FIG. 1;

FIG. 9B is a side cross-sectional view of the shaft shown in FIG. 9A;

FIG. 10A is a perspective view of a shaft cover from the shaft and base unit that is part of the tensioner shown in FIG. 1;

FIG. 10B is a side cross-sectional view of the axle cap shown in FIG. 10A;

FIG. 11 is a perspective view of a tensioner arm from the tensioner shown in FIG. 1;

FIG. 12 is a perspective view of a dampening carrier from the tensioner shown in FIG. 1;

FIG. 13 is a plan view of the dampening carrier shown in FIG. 12 and an alternative tensioner spring to the tensioner spring shown in FIG. 6; and

14-16 are plan views of tensioner springs that may be used in a tensioner that, in operation, radially expands with increased tension in an endless drive member;

FIG. 17 is a perspective view of the shaft and shaft cover;

FIG. 18 is a perspective view of the shaft and second cover;

Fig. 19A to 19C illustrate a method of riveting the shaft cover shown in fig. 17 to the shaft shown in fig. 17.

Detailed Description

A tensioner 100 according to an embodiment of the present disclosure is shown in fig. 1, and the tensioner 100 includes one or more of the following features: the one or more features reduce the overall height of the tensioner 100 as compared to not including any of these features, and the one or more features improve the manufacture of the tensioner 100. Tensioner 100 may be configured to maintain tension in endless drive member 103 on engine 101. The endless drive member 103 in the example shown in fig. 1 is a timing belt, however, the endless drive member 103 may be any other suitable synchronous endless drive member as follows: the synchronous ring drive member transmits rotary power from the crankshaft 104 of the engine 101 to one or more drive components, such as, for example, to a pair of camshafts 105a and 105 b. For convenience and readability, the endless drive member 103 may be referred to as a belt 103 or as a timing belt 103, however, it should be appreciated that any suitable endless drive member may be used.

fig. 2 is an enlarged perspective view of tensioner 100 itself. Fig. 3 and 4 are exploded perspective views of the tensioner 100. Fig. 5 is a cross-sectional view of tensioner 100.

The following describes an overview of components included in tensioner 100. Selected features will be described in greater detail after the summary is provided. Referring to fig. 2-5, tensioner 100 includes a shaft and base unit 114, a bushing 116, a tensioner arm 118, a pulley 120 that rotates on tensioner arm 118, a tensioner spring 122, and a damping carrier 124.

the shaft and base unit 114 may include a shaft 114a, a base 114b, and a shaft cover 114c that are separate from one another but integrally connected by any suitable method, such as, for example, by staking as described further below. The shaft and base unit 114 can be mounted in fixed relation to the engine 101 by any suitable method. For example, the shaft and base unit 114 can be mounted directly to an engine block as shown in fig. 1 via a threaded fastener 119, which threaded fastener 119 can be, for example, a bolt that passes through a fastener aperture 130 in the shaft and base unit 114 into the block of the engine 101. The fastener apertures 130 may be formed by a proximal fastener aperture portion 130a in the shaft 114a (fig. 6) and a distal fastener aperture portion 130b in the shaft cover 114 c. The shaft 114a (and the shaft and base unit 114 As a whole) also includes a central shaft axis As. As can be seen in fig. 5, the fastener apertures 130 themselves extend along a fastener aperture axis Af that is offset relative to the central shaft axis As. This offset allows the position of the shaft and base unit 114 to be adjusted during installation of the tensioner 100 onto the engine 101 (the shaft and base unit 114 is controlled to be proximate to the belt 103 by pivoting the shaft and base unit 114 towards or away from the belt 103).

the shaft having no radial projection

referring to fig. 9A and 9B, fig. 9A and 9B illustrate the shaft 114a from the shaft and base unit 114. In the illustrated embodiment, the shaft 114a has a first axial shaft end 170 and a second axial shaft end 172, and has a radially outer surface 174 that is completely free of any protrusions. In other words, the radially outer surface 174 does not have any shoulders or similar portions. The radially outer surface 174 includes an arm bearing surface shown at 175, which arm bearing surface 175 is the portion of the radially outer surface 174 that supports the tensioner arm 118. Thus, as opposed to prior art shaft and base units which must be fitted in a chuck on the machine to give them a suitable surface finish, the surface 174 can provide a suitable surface finish for engagement with the bushing 116 via the process of passing the surface 174 between the rollers. The surface finish helps to ensure that surface 174 is impregnated with the appropriate amount of polymer from the sleeve so that there is good sliding contact between surface 174 and sleeve 116.

In the illustrated embodiment, the shaft 114a includes an arm bearing portion 176 and a shaft bottom 178, the arm bearing portion 176 being cylindrical and having an arm bearing surface 175 thereon, the shaft bottom 178 being located at the first axial shaft end 170. The shaft bottom portion 178 has a proximal fastener aperture portion 130 a. The shaft 114a is open at a second axial shaft end 172. The shaft cover 114c (shown in fig. 10) covers the second axial shaft end 172 and includes a flange 180 and a distal fastener aperture portion 130 b. The shaft cover 114c is movable on the second axial shaft end 172 to a position where the distal fastener aperture portion 130b aligns with the proximal fastener aperture portion 130a to form the fastener aperture 130.

Shaft cover mounted to the inside of a pivot shaft

the shaft cover 114c includes an axial projection 186 having a radially outer locating surface 187 thereon, the radially outer locating surface 187 engaging a radially inner surface 188 of the shaft 114a at the open second axial shaft end 172.

the shaft cover 114c includes a tool receiving area 190, the tool receiving area 190 receiving the following tools: the tool allows the user to adjust the position of the shaft and base unit 114 relative to the engine 101, or in some embodiments, the position of the shaft cover 114c relative to the shaft 114 a.

The flange 180 axially retains the tensioner arm 118 on the shaft 114a and may therefore be referred to as an arm retaining portion 180. It can be seen that by positioning the shaft cover 114c using the inner surface 188 of the shaft 114a instead of the outer surface, the overall height of the tensioner 100 can be kept low. In contrast, if shaft cover 114c were positioned using radially outer surface 174 of shaft 114a, shaft cover 114c would have to include a portion that extends axially toward first axial shaft end 170 so as to have some axial overlap with radially outer surface 174 of shaft 114 a. If the arm 118 extends close to the second axial shaft end 172 in the example shown in the drawings, the shaft cover 114c will have an effect on the tensioner arm 118 itself. Therefore, to increase some clearance, the shaft 114a would have to be made taller, which would increase the overall height of the tensioner. In contrast, by positioning the shaft cover 114c on the radially inner surface 188 of the shaft 114a, the flange 180 itself retains the arm 118 and the shaft 114a can be kept shorter.

the tensioner arm 118 is pivotally mounted to the shaft 114a (or more generally to the shaft and base unit 114) for pivotal movement about an arm pivot axis, which is the central shaft axis As. The pivotal movement in the first direction D1 (fig. 1) may be referred to as movement in the free arm direction. The pivotal movement in the second direction D2 (fig. 1) may be referred to as movement in the load stop direction.

The arms having no radial projections

referring to fig. 11, tensioner arm 118 has a first axial arm end 196 and a second axial arm end 198, and further includes a radially outer surface 200, the radially outer surface 200 including a pulley bearing surface 202, and the radially outer surface 200 extending from the first axial arm end 196 to the second axial arm end 198 and being completely free of any radial protrusions. The tensioner arm 118 also includes a radially inner surface 203 that defines an arm pivot axis As.

the second axial arm end 198 is on an axial projection 199 having a first circumferential side 201, the first circumferential side 201 being a free arm stop engaging surface. The shaft cover 114c has a free arm stop 207 located thereon. Movement of the tensioner arm 118 in the first direction D1 (fig. 1) causes the free arm stop engagement surface to face the free arm stop.

Bushing 116 is present between radially inner surface 203 of tensioner arm 118 and arm bearing surface 175 and facilitates pivotal movement of tensioner arm 118 on the shaft and base unit 114. The bushing 116 may be made of any suitable material, such as Stanyl TW371 (which is a material based on nylon PA 46) and provided by DSM Engineering Plastics, inc (DSM Engineering Plastics, b.v.).

The pulley 120 is rotatably mounted to the tensioner arm 118 (e.g., via a bearing 121 or any other suitable means) for rotation about a pulley axis Ap that is offset relative to the arm pivot axis As by a selected offset distance: the offset distance is less than the radius of the pulley 120 at the endless drive member engaging surface 150 (shown at Rp). The pulley 120 has an annular drive member engaging surface 150 that engages the annular drive member 103. Pulley 120 is only one example of an endless drive member engagement member that can be mounted to tensioner arm 118 and that can engage endless drive member 103.

The bearings 121 may be provided by a plurality of rolling elements 121a (e.g., balls) and inner and outer races 121b and 121c, respectively. The inner race 121b may be a separate member that is typically provided on a bearing, however, the outer race 121c may be formed directly in the radially inner surface of the pulley 120. This reduces the number of parts that must be manufactured.

Riveting of shaft caps to shafts without projections

Referring to fig. 17, 18, 19A, and 19B, fig. 17, 18, 19A, and 19B illustrate an alternative embodiment of the shaft 114 a. In this alternative embodiment, the shaft 114a is riveted to a shaft cover, shown at 114 c. It can be seen that the shaft 114a has a cylindrical body 240 without axial projections. The shaft cover 114c has a plurality of staking apertures 242 about the periphery of the shaft 114a, the plurality of staking apertures 242 exposing the second axial shaft end 172. The shaft cap 114c also includes a staking shoulder 244 positioned proximate the second (distal) end 172 but spaced from the second (distal) end 172 toward the first (proximal) end 170. To assemble the shaft cover 114c to the shaft 114a, the shaft cover 114c is positioned on the second (distal) end 172 of the shaft 114 a. The staking protrusion 250 is inserted into the staking aperture 242 to engage the second end 172 of the shaft 114 a. The staking tabs 250 deform the second end 172 such that the second end 172 projects radially outward onto the staking shoulder 244, thereby locking the shaft cap 144c in place.

in some embodiments, the shaft cap 114c (fig. 20) has a staking shoulder 254 radially inward of the cylindrical body 240 of the shaft 114a, and the staking protrusion 250 deforms the second end 172 such that the second end 172 projects radially inward onto the staking shoulder 244. Thus, more broadly, the staking protrusion 250 may deform the second end 172 such that the second end 172 projects radially beyond the staking shoulder 244.

a bottom cover 114d is shown on the shaft 114a instead of providing a unitary member including a bottom. Bottom cap 114d includes an orifice portion 130 a.

tensioner spring to prevent tangling

Tensioner spring 122 is positioned to rotationally urge tensioner arm 118 to urge tensioner arm 118 in a first rotational direction (i.e., the free arm direction) to drive pulley 120 into timing belt 103, and belt 103 applies a force to pulley 120 against the urging of spring 122 to urge tensioner arm 118 in the load stop direction.

As shown in fig. 3-5, the tensioner spring 122 may be a helical torsion spring having a first end 122a and a second end 122 b. The spring 122 may comprise a plurality of coils 123, wherein a coil is a section of the spring 122 that extends over 360 degrees. In this example, referring to fig. 8B, the spring 122 has about three coils. The shaft and base unit 114 is positioned to receive torque from the first spring end 122a and the tensioner arm 118 is positioned to receive torque from the second spring end 122 b.

During manufacture of the tensioner, it is preferable for such manufacture to be performed automatically (i.e., by a machine rather than an assembly worker) in order to reduce the labor used to produce the tensioner. However, in prior art tensioners, it is difficult for the machine to grasp the tensioner spring from the case with such a spring for insertion into the tensioner because the springs have a tendency to tangle with each other while in the case. Accordingly, assembly workers sometimes manually grasp the spring from the case, unwrap the grasped spring if necessary and then insert the unwrapped spring into the tensioner, thus slowing production and increasing the manufacturing cost of the tensioner.

Referring to fig. 6, fig. 6 shows a cross-sectional view of the tensioner spring 122, in some embodiments, the spacing between any two adjacent coils of the plurality of coils 123 to enter the tensioner spring is less than the width of each coil of the plurality of coils 123 so as to prevent the tensioner spring from winding with another identical tensioner spring 122. The spacing between any two adjacent coils 123 to enter is shown at S. The width of the coil 123 of the spring 122 is shown as Wc. As can be seen, the spacing S is less than the width Wc. It will be appreciated that the spacing S is not the same as the gap between the coils 123. The gap between the coils 123 is the distance between the points on adjacent coils 123 that are closest to each other. For the spring 122 shown in fig. 6, the gap is shown at G. While it is useful to have the gap G smaller than the width of the coils, there is still a tendency for the coils on one spring to wedge a pair of adjacent coils intermittently onto the adjacent spring as the springs are urged toward each other, depending on the shape of the coils. If there are many "introducers" to the coil shape, the gap G may be small but the spacing S may be large, which may facilitate wedging apart of adjacent coils.

Based on the foregoing, it has been found that forming the springs such that the spacing S is less than the width Wc of the coils further helps to inhibit tangling between the springs, as exemplified by spring 122 (shown as 122' and 122 ", respectively) shown in fig. 6. In fig. 6, the identified spacing S is the maximum spacing S that exists for the spring 122. In other words, this is the worst case description. The width Wc is shown as the width of the coil 123 of the spring 122 "closest to the spacing S of the spring 122'. The width of the coils 123 of the springs 122 'and 122 "may be substantially constant, or the width of the coils 123 of the springs 122' and 122" may vary along the length of the spring 122.

It should be noted that there are other optional features of the springs 122 that help inhibit entanglement with adjacent springs 122. For example, it can be seen that the spring 122 is made of wire having a generally rectangular cross-sectional shape. Therefore, the size of the space S is relatively closer to the size of the gap G between the adjacent coils 123 than a spring made of a wire material having a circular cross-sectional shape.

Another optional feature is that the plurality of coils 123 are generally arranged in a generally helical manner about a longitudinal axis (shown with Aspr) and generally increase in distance from the axis Aspr in the longitudinal direction. In other words, the spring 122 has a generally conical shape. It should be noted that the conical shape itself reduces the possibility of tangling, since the gap G and the spacing S are generally in a radial direction, and thus penetration of the gap G or spacing S is achieved by a vertical force acting on the springs 122' and 122 ". It should be noted, however, that the shape of the coils 123 of the springs 122' and 122 "is generally helical (as shown in fig. 7). Thus, the arcs of the coils 123 inhibit penetration by the coils 123 of adjacent springs, which arcs are in opposite directions. In contrast to the generally conical shaped springs shown in the drawings, this is not the case for springs having a generally cylindrical shape.

In other words, during an increase in tension in endless drive member 103, tensioner arm 118 is positioned to move in a second direction D2 opposite first direction D1, and tensioner spring 122 is positioned to radially expand away from longitudinal axis Aspr or As in response to movement of tensioner arm 118 in second direction D2.

In some embodiments, another optional feature that helps prevent tangling between adjacent springs 122 is that the tensioner springs 122 do not have tangs, as shown in fig. 7. The spring 122 is sometimes referred to as an "open" spring in the sense that, during movement of the tensioner arm 118 in the load stop direction, the ends 122a and 122b of the spring abut only the shaft and base unit 114, the surface of the tensioner arm 118, and the curved portion of the spring 122, causing the coils 123 of the spring 122 to open radially. This is in contrast to closed springs, which are commonly used in some tensioners of the prior art, and which require that the ends of the spring have tangs that hook into corresponding grooves in the tensioner arm and shaft and base unit, and wherein the bent portion of the spring radially tightens the coils of the spring during movement of the tensioner arm 118 in the load stop direction.

When the spring is formed with a tang, there is a natural radius at the bend in the wire of the spring where the tang begins. An example of such a spring is shown at 160 in fig. 8. The spring 160 has a plurality of coils 161 and first and second ends with tangs thereon as shown at 162. At the start of the tang 162, the radius of the bend in the spring wire provides a relatively large spacing S and is therefore easily penetrated by coils from adjacent springs.

All of these aforementioned features of the spring 122 help to inhibit tangling of the spring 122 with an adjacent spring 122. Accordingly, the spring 122 may be more easily picked up from the magazine and inserted into the tensioner by a machine (e.g., an assembly robot), thereby facilitating automated assembly of the tensioner. It has been found that there is about a 1% entanglement rate in the testing of the spring 122, while other springs of the prior art have been found to have entanglement rates in excess of 80%.

damping carrier

A damping carrier 124 (fig. 12 and 13) retains the tensioner spring 122 and provides some of the damping that is present in the tensioner 100 (while other damping is provided by the friction fit between the tensioner arm 122 and the bushing 116). In this example, the damping carrier 124 includes a spring end engagement slot 204 positioned to retain the second spring end 122 b. Thus, the second spring end 122b transmits torque to the tensioner arm 118 through the wall 205 of the damping carrier 124. The wall 205 engages an arm torque transmitting surface 206 (fig. 13) on the tensioner arm 118. The arm torque transmission surface 206 may be provided on an axial protrusion 208 on the tensioner arm 118.

To provide damping, the damping carrier 124 includes a damping surface 210 thereon. In the example shown, the damping surface 210 is disposed on a radially inner surface 211 of the damping carrier 124. In the example shown, the damping surface 210 is disposed on the axial protrusion 212 and has an angular width of approximately 120 degrees, although other angular widths, such as angular widths greater than 120 degrees, may also be used. During the transmission of torque between the tensioner spring 122 and the tensioner arm 118 (shown in fig. 13), a force F is applied by the tensioner arm 118 (particularly from the torque transmission surface 206 on the axial protrusion 208) into the assembly of the spring 122 and the damping carrier 124. The direction of force F may be substantially tangential to spring 122 at second spring end 122 b. The force F results in a certain force being transferred from the first spring end 122a into the base 114 b. The force transferred into base 114b results in a reaction force, shown at F3, being transferred from base 114b into first spring end 122 a.

Based on the position and orientation of the forces F and F3 (and thus the position of the first and second ends 122a and 112b of the tensioner spring 122), the damping carrier 124 is pivoted about a carrier torque receiving surface, shown at 209, which carrier torque receiving surface 209 engages the torque transmitting surface 206 on the tensioner arm 118. This pivoting of the damping carrier 124 causes the damping surface 210 to engage a portion of the outer surface 174 of the shaft 114a, thereby causing damping to occur between the damping carrier 124 and the shaft 114 a. This portion of the outer surface 174 may be referred to as a damping surface 177. The damping surface 210 may be referred to as a first damping surface 210 and the damping surface 177 may be referred to as a second damping surface, in this embodiment, the damping surface 177 is on the shaft 114 a.

However, in an alternative embodiment, the first damping surface 210 is disposed on a radially outer surface of the damping carrier 124 and the second damping surface 177 is disposed on a radially inner surface of the shaft and base unit 114 (e.g., as part of a radially inner surface 222 (fig. 16) of an outer lip 223 of the base 114 b). In such an alternative embodiment, the damping carrier 124, tensioner spring 122 and tensioner arm 118 may be arranged such that pivoting of the damping carrier 124 drives the radially outer first damping surface 210 against the radially inner second damping surface 177, as shown in fig. 16.

in another alternative embodiment, the damping carrier 124 may be disposed at the first end 122a of the tensioner spring 122 instead of the second end 122 b. In such embodiments, the first damping surface 210 may be disposed on one of a radially inner or outer surface of the damping carrier 124, while the second damping surface 177 is disposed on a complementary surface of the tensioner arm 118.

based on the above, it can be said that the damping carrier 124 includes a spring end engagement groove (i.e., spring end engagement groove 204) that holds one of the first and second spring ends (122a, 122 b). The damping carrier 124 also includes a first damping surface 210 thereon, wherein the first spring end 122a, the second spring end 122b, and the first damping surface 210 are positioned relative to one another such that the damping carrier 124 pivots during force transfer between the tensioner arm 118 and the shaft and base unit 114 through the tensioner spring 122 so as to drive the first damping surface 210 into the tensioner arm 118 and a complementary second damping surface 177 on either of the shaft and base unit 114 that receives torque from the other of the first spring end 122a and the second spring end 122 b.

As can be seen in fig. 13, the second spring end 122b and the radially inner damping surface are oriented relative to each other such that a tangential force (e.g., a purely tangential force, or alternatively a tangential force that is a vector component of a non-tangential force) from the tensioner arm 118 on the tensioner spring 122 at the second spring end 122b generates a reaction force F2 on the radially inner damping surface 210 through the shaft and base unit 114, thereby generating frictional damping during movement of the tensioner arm 118 relative to the shaft and base unit 114 about the arm pivot axis As. The force F2 shown in FIG. 13 is shown as a point force, however the actual force F2 is a distributed force that is distributed over some or all of the angular width of the radially inner damping surface 210. The point force F2 shown in fig. 13 is a mathematical representation equivalent to a distributed force. A force F3 will be exerted on the tensioner spring 122 by the shaft and a drive surface 212 (fig. 4) on the base unit 114 (e.g., on an edge surface of the lip 223 on the base 114 b), the drive surface 212 engaging the first end 122a of the tensioner spring 122. Force F3 (fig. 13) may be tangent to tensioner spring 122 at first end 122 a.

gradual locking of springs

Fig. 14, 15A, 15B and 16 illustrate another aspect of the operation of the tensioner spring 122. More specifically, it can be seen that the coils 123 of the tensioner spring 122 are arranged about the longitudinal axis Aspr such that the coils 123 are radially offset from each other but axially overlap each other; in other words, the coils 123 of the spring 122 may be considered to have a generally helical arrangement, even when there is some axial offset between the coils 123 and 123. As described above, the plurality of coils 123 includes the radially outermost coil 123o and at least one inner coil 123 i. In the example shown in fig. 14, there are outer coils 123o, and there are 1.5 inner coils 123 i. One of the tensioner arm 118 and the shaft and base unit 114 has a spring limiting surface 222 thereon (e.g., on a lip 223). In the present example, as can be seen in fig. 5, the spring limiting surface 222 is shown as a radially inner surface of the base 114 b.

as seen in fig. 5 and 14, when there is a relatively low tension in the endless drive member 103 (fig. 1), the coils 123 may be spaced apart from each other and the outer coils may be spaced apart from the spring restraining surface 222.

As the tension in the endless drive member 103 (fig. 1) increases, the tensioner spring 122 is progressively locked by the coils 123 progressively expanding into engagement with each other and the radially outermost coils 123o progressively expanding into engagement with the spring limiting surface 222. In the illustrated embodiment, the outermost coil 123o is stretched into engagement with the spring restraining surface 222, the next innermost coil (shown as 123i 1) is stretched radially into engagement with the outermost coil 123o, and the still further innermost coil (which is a coil that is part of the coil shown as 123i 2) is stretched radially into engagement with coil 123i1, as shown in fig. 15B. The position shown in fig. 15B may be referred to as a load stop position. Fig. 15A shows an intermediate state in which the outermost coil 123o is stretched into engagement with the spring limiting surface 222.

the spring rate of tensioner spring 122 gradually increases due to the gradual engagement of coils 123 with each other and with spring limiting surface 222. Once all of the coils 123 are engaged with each other and with the restraining surface 222, the spring 122 provides a secure connection between the tensioner arm 118 and the shaft and base unit 114 (i.e., the spring 122 has virtually an infinite spring load rate). It should be noted that this is an improvement over tensioners where the spring is a helical coil spring (i.e., has a generally cylindrical overall shape). If such a tensioner employs a limiting surface, the spring will rapidly increase its spring load rate as it engages the limiting surface until the spring fully engages the limiting surface and provides a secure connection. The rapid increase in spring rate to infinity can lead to impact loads and ultimately to failure of some components of the tensioner.

Another feature to be noted in the tensioner 100 is that in some embodiments, such as the embodiment shown in the figures, the tensioner spring 122 acts as a load stop for the tensioner 100, in the sense that the spring 122 itself acts to limit travel of the tensioner arm 118 in the load-stop direction, because as described above, once the tensioner arm 118 has fully traveled, all of the coils 123 of the spring 122 engage each other and with the limiting surface 222, such that the spring 122 provides a secure connection between the tensioner arm 118 and the shaft and base unit 114, which in use, the shaft and base unit 114 itself is fixedly connected to a fixed structure, such as an engine block. In other words, when the tension in the endless drive member 103 increases to a selected tension, radial expansion of the plurality of coils 123 is prevented by engagement of the plurality of coils 123 with at least the spring limiting surface 222. In the present embodiment, when the tension in the endless drive member 103 is increased to a selected tension, radial expansion of the plurality of coils 123 is prevented by engagement of the plurality of coils 123 with each other and with the spring limiting surface 222.

Although the spring restraining surface 222 is disclosed as being a radially inner surface of the base 114b, it should be understood that the spring restraining surface 222 may alternatively be selected as any other surface, such as a radially outer surface of the shaft 114, a radially inner surface of the arm 118, or any other suitable location.

It should be noted that the frictional damping force is proportional to the force (and thus the torque) exerted by the tensioner arm 118 on the second spring end 122 b. This is different from the damping force provided by bushing 116, which is proportional to the radial force of tensioner arm 118 on bushing 116, which is in turn proportional to the hubload on pulley 120.

There is also a shaft indicia 182 (fig. 2) on the shaft cover 114c, the shaft indicia 182 in the illustrated example may be a notch on the flange 180. The tensioner arm 118 has an arm mark 184 located thereon at an axial end. Arm indicia 184 and shaft indicia 182 mate during installation of tensioner 100 on engine 101. More specifically, installation of tensioner 100 may proceed as follows:

Tensioner 100 is installed by passing fastener 119 through fastener aperture 130 and into an aperture in a member that is fixed relative to engine 101, such as an engine block. The fastener 119 is not initially fully tightened. Thus, the shaft and base unit 114 can be rotated while maintaining the tensioner arm 122 in a substantially constant position with the belt 103 (fig. 1) engaged with the pulley 120 to adjust the amount of preload present in the tensioner spring 122 when the engine 101 is shut down, which in turn adjusts the amount of tension present in the belt 103 (fig. 1). The shaft and base unit 114 is rotated until the shaft mark 182 is aligned with the arm mark 184. The fastener 119 is then tightened to hold the shaft and base unit 114 in that position. Thus, during use, when the engine 101 is shut down, the arm indicia 184 is aligned with the shaft indicia 182.

By providing a separate shaft cover 114c, the shaft 114a can be manufactured without any raised surface 174. In contrast, prior art shaft and base units typically have flange portions for retaining the tensioner. However, it is less expensive to manufacture the shaft 114a and the shaft cover 114c as separate elements that are mechanically connected via fasteners 119 (which fasteners 119 are required in any event to mount the tensioner 100 to the engine 101) than to manufacture a single shaft member with an integral flange.

It should be noted that in some embodiments, the pulley 120 has a swept volume V (i.e., the volume occupied), the pulley 120 being generally shaped as a thick disc and shown in side view in fig. 19A. In some embodiments, tensioner spring 122 is positioned substantially entirely within swept volume V of pulley 120 due to the generally conical shape of the spring.

the above-described embodiments are intended to be examples only, and variations and modifications thereof may be made by those skilled in the art.

Claims

1. A tensioner for an endless drive member, the tensioner comprising:

A shaft and base unit mountable to be fixed relative to an engine block;

A tensioner arm pivotable relative to the shaft and base unit about a tensioner arm axis;

A pulley rotatably mounted to the tensioner arm for rotation about a pulley axis offset from the tensioner arm axis, wherein the pulley is engageable with an endless drive member;

A tensioner spring positioned to urge the tensioner arm in a first direction about the tensioner arm axis, wherein the tensioner spring is a torsion spring having a first spring end and a second spring end and a plurality of coils between the first spring end and the second spring end, wherein the shaft and base unit are positioned to receive torque from the first spring end and the tensioner arm is positioned to receive torque from the second spring end; and

A damping carrier including a spring end engagement slot retaining one of the first and second spring ends, wherein the damping carrier further includes a first damping surface thereon, and wherein the first spring end, the second spring end, and the first damping surface are positioned relative to one another such that the damping carrier pivots during force transfer between the tensioner arm and the shaft and base unit through the tensioner spring so as to drive the first damping surface into a complementary second damping surface on either of the tensioner arm and the shaft and base unit that receives torque from the other of the first and second spring ends.

2. A tensioner as claimed in claim 1, wherein the first spring end, the second spring end, and the first damping surface are positioned relative to each other such that a moment that causes the damping carrier to pivot relative to the tensioner arm and the complementary second damping surface is on the shaft and base unit.

3. A tensioner as claimed in claim 1, wherein the first damping surface is a radially inner damping surface of the damping carrier.

4. the tensioner of claim 3 wherein the radially inner damping surface is positioned radially inward of at least one of the coils.

5. The tensioner of claim 1 further comprising a bushing positioned radially between the shaft and base unit and the tensioner arm to radially support the tensioner arm on the shaft and base unit.

6. A tensioner as claimed in claim 1, wherein the first and second ends are urged by the shaft and base unit and the tensioner arm, respectively, during transmission of torque between the first and second ends so as to radially expand the coil.

7. The tensioner of claim 1 wherein the first damping surface is circumferentially spaced from both the first spring end and the second spring end.

8. A tensioner as claimed in claim 1, wherein at least a portion of the first damping surface is circumferentially 90 degrees from the second spring end.

9. A tensioner as claimed in claim 1, wherein the tensioner spring is a coil spring that includes a plurality of coils that are radially offset from one another.

10. A method of assembling a shaft cover onto a shaft for a tensioner, the method comprising:

Providing a shaft cover;

Disposing the shaft cap on one of the first and second axial shaft ends, wherein the shaft cap has a plurality of staking apertures exposing the one of the first and second axial shaft ends, wherein the shaft cap further includes a staking shoulder positioned proximate to but spaced from the one of the first and second axial shaft ends toward the other of the first and second axial shaft ends;

deforming the one of the first and second axial shaft ends using the staking projection such that the one of the first and second axial shaft ends projects radially over the staking shoulder, thereby locking the shaft cap to the shaft.

11. the method of claim 10, wherein the deforming step includes deforming the one of the first and second axial shaft ends using the staking protrusion such that the one of the first and second axial shaft ends projects radially outward onto the staking shoulder, thereby locking the shaft cap to the shaft.

12. A tensioner for an endless drive member, the tensioner comprising:

A shaft and base unit mountable to be fixed relative to an engine block;

A pulley rotatably mounted to the tensioner arm for rotation about a pulley axis offset from the tensioner arm axis, wherein the pulley is engageable with the endless drive member, wherein the pulley has a swept volume; and

A tensioner spring positioned to urge the tensioner arm in a first direction about the tensioner arm axis, wherein the tensioner spring is a torsion spring having a first spring end and a second spring end and a plurality of coils between the first spring end and the second spring end, wherein a diameter of the plurality of coils decreases from one of the first and second spring ends to the other of the first and second spring ends, wherein one of the first and second spring ends is positioned to transmit torque into the shaft and base unit, and the other of the first and second spring ends is positioned to transmit torque into the tensioner arm, wherein the tensioner spring is positioned substantially entirely within the swept volume of the pulley.

13. A tensioner for an endless drive member, the tensioner comprising:

A shaft and base unit mountable to be fixed relative to an engine, wherein the shaft and base unit includes fastener apertures to allow fasteners to pass through to fixedly connect the shaft and base unit to the engine;

A pulley rotatably mounted to the tensioner arm for rotation about a pulley axis offset from the tensioner arm axis, wherein the pulley is engageable with the endless drive member;

a tensioner spring positioned to urge the tensioner arm in a first direction relative to the shaft and base unit, wherein the tensioner spring comprises a plurality of coils arranged about a longitudinal axis such that the coils are radially offset from each other but axially stacked on each other, wherein the plurality of coils comprises a radially outermost coil and at least one inner coil;

wherein the tensioner arm and one of the shaft and base unit have spring limiting surfaces, and wherein radial expansion of the plurality of coils is prevented by engagement of the plurality of coils with at least the spring limiting surfaces when the tension in the endless drive member increases to a selected tension.

14. A tensioner as claimed in claim 13, wherein when the tension in the endless drive member increases to the selected tension, radial expansion of the plurality of coils is prevented by engagement of the plurality of coils with each other and with the spring limiting surface.

15. a tensioner for an endless drive member, the tensioner comprising:

wherein the tensioner arm and one of the shaft and base unit have spring limiting surfaces, and wherein the tensioner spring is progressively locked as the tension in the endless drive member increases by the coils progressively expanding into engagement with each other and the radially outermost coils progressively expanding into engagement with the spring limiting surfaces.

16. a tensioner for an endless drive member, the tensioner comprising:

A shaft and base unit mountable to be fixed relative to an engine, wherein the shaft and base unit includes a fastener aperture to allow a fastener to pass through to fixedly connect the shaft and base unit to the engine, and wherein the shaft and base unit includes a base and a shaft separate from the base and having the base mounted thereon, wherein the shaft has an axis and has a first axial shaft end and a second axial shaft end, wherein the shaft has a radially outer surface that includes an arm support surface and that extends from the first axial shaft end to the second axial shaft end without any radial projection at all;

a tensioner arm pivotally supported on the arm support surface of the shaft for pivotal movement about a tensioner arm axis;

A pulley rotatably mounted to the tensioner arm for rotation about a pulley axis offset from the tensioner arm axis, wherein the pulley is engageable with an endless drive member; and

a tensioner spring positioned to urge the tensioner arm in a first direction relative to the shaft and base unit, wherein the tensioner spring has a first end, a second end, and a plurality of coils between the first end and the second end, wherein the first end is positioned to transmit torque with the base and the second end is positioned to transmit torque with the tensioner arm.

17. a tensioner as claimed in claim 16, wherein the tensioner arm is pivotally supported on the radially outer surface of the shaft via a bushing that is supported directly on the radially outer surface of the shaft.

18. A tensioner as claimed in claim 16, wherein the shaft includes an arm support portion that is cylindrical and has the arm support surface thereon and a shaft bottom that is located at the first axial shaft end, wherein the shaft bottom has a proximal fastener aperture portion, and wherein the shaft is open at the second axial shaft end, wherein the shaft and base unit further includes a shaft cover that covers the second axial shaft end and includes an arm retaining portion that axially retains the tensioner arm on the shaft, and the shaft cover includes a distal fastener aperture portion and is movable over the second axial shaft end of the shaft to a position where the distal fastener aperture portion aligns with the proximal fastener aperture portion to form the fastener aperture, wherein the shaft has a radially inner locating surface at the second axial shaft end, and wherein the shaft cap has a radially outer locating surface that engages the radially inner locating surface on the shaft to locate the distal fastener aperture portion relative to the proximal fastener aperture portion.

19. The tensioner of claim 16 wherein the shaft cap has a free arm stop thereon and wherein the second axial arm end is on an axial projection having a first circumferential side that is a free arm stop engagement surface, wherein movement of the tensioner arm in the first direction causes the free arm stop engagement surface to face the free arm stop.

20. a tensioner as claimed in claim 19, wherein the tensioner arm has an arm mark on the tensioner arm at the second axial arm end, and wherein the shaft cover has a shaft mark on the shaft cover, wherein, during use, when the engine is off, the arm mark is aligned with the shaft mark.

21. The tensioner of claim 16 wherein the pulley is a unitary member having a radially inner surface that is a first ball-engaging surface, and wherein the tensioner further comprises:

an inner race press-fit onto the pulley support surface and including a radially outer surface as a second ball engaging surface; and

a plurality of balls rotatably supporting the pulley on the inner race.

22. A tensioner as claimed in claim 16, further comprising a damping carrier including a spring end engagement slot positioned to retain the second spring end, wherein the damping carrier further includes a radially inner damping surface thereon, and wherein the second spring end and the radially inner damping surface are positioned such that a tangential force on the second spring end during the transmission of torque moves the damping carrier to frictionally engage the radially inner damping surface with the shaft and base unit or in an increased frictional engagement with the shaft and base unit.

23. A tensioner as claimed in claim 16, wherein the plurality of coils are spaced apart from one another by a coil-to-coil gap, and wherein a spacing between any two adjacent coils of the plurality of coils to enter the tensioner spring is less than a width of each coil of the plurality of coils so as to prevent the tensioner spring from tangling with another identical tensioner spring.

24. a tensioner as claimed in claim 16, wherein the plurality of coils are arranged in a generally helical manner about a longitudinal axis and are radially spaced from one another and generally increase in distance from the axis in the longitudinal direction.

25. A tensioner for an endless drive member, the tensioner comprising:

a tensioner arm pivotable about an arm pivot axis relative to the shaft and base unit, wherein the tensioner arm has a first axial arm end and a second axial arm end, wherein the tensioner arm has a radially outer surface that includes a pulley bearing surface and extends from the first axial arm end to the second axial arm end without any radial protrusions at all;

a pulley rotatably supported on the pulley support surface of the tensioner arm for rotation about a pulley axis offset from the tensioner arm axis, wherein the pulley is engageable with an endless drive member;

A bushing positioned radially between the shaft and base unit and the tensioner arm to radially support the tensioner arm on the shaft and base unit; and

A tensioner spring positioned to urge the tensioner arm in a first direction about the tensioner arm axis.

26. a tensioner as claimed in claim 25, wherein the shaft and base unit includes a base and a shaft separate from the base and having the base mounted thereon, wherein the shaft has an axis and has a first axial shaft end and a second axial shaft end, wherein the shaft has a radially outer surface that includes an arm bearing surface and that extends from the first axial shaft end to the second axial shaft end without any radial protrusions at all,

And wherein the tensioner spring has a first end, a second end, and a plurality of coils between the first end and the second end, wherein the first end is positioned to transmit torque with the base and the second end is positioned to transmit torque with the tensioner arm.

27. A tensioner as claimed in claim 26, wherein the tensioner arm is pivotally supported on the shaft via a bushing that is directly supported on the arm support surface.

28. a tensioner as claimed in claim 26, wherein the shaft includes an arm support portion that is cylindrical and has the arm support surface thereon and a shaft bottom that is located at the first axial shaft end, wherein the shaft bottom has a proximal fastener aperture portion, and wherein the shaft is open at the second axial shaft end, wherein the shaft and base unit further includes a shaft cover that covers the second axial shaft end and includes an arm retaining portion that axially retains the tensioner arm on the shaft, and the shaft cover includes a distal fastener aperture portion and is movable over the second axial shaft end of the shaft to a position where the distal fastener aperture portion aligns with the proximal fastener aperture portion to form the fastener aperture, wherein the shaft has a radially inner locating surface at the second axial shaft end, and wherein the shaft cap has a radially outer locating surface that engages the radially inner locating surface on the shaft to locate the distal fastener aperture portion relative to the proximal fastener aperture portion.

29. A tensioner as claimed in claim 28, wherein the shaft cap has a free arm stop thereon, and wherein the second axial arm end is on an axial projection having a first circumferential side that is a free arm stop engagement surface, wherein movement of the tensioner arm in the first direction causes the free arm stop engagement surface to face the free arm stop.

30. a tensioner as claimed in claim 28, wherein the tensioner arm has an arm mark on the tensioner arm at the second axial arm end, and wherein the shaft cover has a shaft mark on the shaft cover, wherein, during use, when the engine is off, the arm mark is aligned with the shaft mark.

31. The tensioner of claim 25 wherein the pulley is a unitary member having a radially inner surface that is a first ball-engaging surface, and wherein the tensioner further comprises:

a plurality of balls rotatably supporting the pulley on the inner race.

32. A tensioner as claimed in claim 25, further comprising a damping carrier including a spring end engagement slot positioned to retain the second spring end, wherein the damping carrier further includes a radially inner damping surface thereon, and wherein the second spring end and the radially inner damping surface are oriented relative to each other such that a tangential force from the tensioner arm on the tensioner spring at the second spring end results in a reaction force on the radially inner damping surface by the shaft and base unit, thereby creating frictional damping during movement of the tensioner arm relative to the shaft and base unit about the arm pivot axis.

33. A tensioner as claimed in claim 25, wherein the plurality of coils are spaced apart from one another by a coil-to-coil gap, and wherein a spacing between any two adjacent coils of the plurality of coils to enter the tensioner spring is less than a width of each coil of the plurality of coils so as to prevent the tensioner spring from tangling with another identical tensioner spring.

34. A tensioner as claimed in claim 25, wherein the plurality of coils are arranged in a generally helical manner about a longitudinal axis and are radially spaced from one another and generally increase in distance from the axis in the longitudinal direction.

35. a tensioner for an endless drive member, the tensioner comprising:

A pulley having an endless drive member engagement surface engageable with an endless drive member, wherein the pulley is rotatably mounted to the tensioner arm for rotation about a pulley axis that is offset from the tensioner arm axis by an offset distance that is less than a radius of the pulley at the endless drive member engagement surface; and

A tensioner spring positioned to urge the tensioner arm in a first direction relative to the shaft and base unit, wherein the tensioner spring comprises a plurality of coils spaced apart from each other by a coil-to-coil gap, and wherein a spacing between any two adjacent coils of the plurality of coils to enter the tensioner spring is less than a width of each coil of the plurality of coils so as to prevent the tensioner spring from tangling with another identical tensioner spring.

36. a tensioner as claimed in claim 35, wherein the tensioner spring is made of wire having a substantially rectangular cross-sectional shape.

37. a tensioner as claimed in claim 35, wherein the plurality of coils are arranged in a generally helical manner about a longitudinal axis and generally increase in distance from the axis in the longitudinal direction.

38. The tensioner of claim 35 wherein the tensioner spring is tang-free.

39. a tensioner as claimed in claim 35, wherein the tensioner arm is positioned to move in a second direction opposite the first direction during an increase in tension in the endless drive member, and wherein the tensioner spring is positioned to radially expand away from the longitudinal axis in response to movement of the tensioner arm in the second direction.

40. A tensioner for an endless drive member, the tensioner comprising:

A tensioner spring positioned to urge the tensioner arm in a first direction relative to the shaft and base unit, wherein the tensioner spring comprises a plurality of coils arranged in a generally helical manner about a longitudinal axis and radially spaced from one another and generally increasing in distance from the axis in the longitudinal direction.