Clamping device with increased damping and an arm-on-base shell configuration

Abstract

Tensioning device (200) for maintaining the tension of an endless drive member, comprising: a base comprising a base shell (202) which can be mounted stationary relative to a motor and has a peripheral wall (212) defining an arm pivot axis (Aa), an arm (204) having a radially outer arm surface (220) and a radially inner arm surface (222) defining a pulley axis (Ap) parallel to and offset from the arm pivot axis (Aa), a sleeve (208) arranged between the radially outer arm surface (220) and the peripheral wall (212) of the base shell (202), wherein the arm (204) is rotatably held in the base shell (202) by means of the sleeve (208), a pulley (203) having a radially inner pulley wall (230) rotatably mounted on the radially inner arm surface (222) for rotation about the pulley axis (Ap), and having a radially outer pulley wall (232) disposed radially outside the base shell (202) and engageable with an endless drive member, and a tension spring (206) arranged to bias the arm (204) in a first direction about the arm pivot axis (Aa), characterized in that a mounting wall (209) of the base shell (202) has a fastener through-opening (210) for receiving a mounting fastener (211), and wherein the radially inner pulley wall (230) defines an axially extending central opening (234) providing access to the fastener through-opening (210).

Description

Field of invention

[0001] The invention relates generally to the field of tensioning devices for endless drive links such as chains or timing belts. Background of the invention

[0002] Many engines in vehicles today use a timing belt to drive certain components that require specific synchronization with the rotation of the engine, such as the camshafts that control the opening and closing of the valves to the cylinders. Tensioners to maintain timing belt tension play an important role because a loss of tension in a timing belt can cause the timing belt to jump teeth on the pulleys to which it is connected. This leads to a loss of synchronization between components such as the valves and the engine. Such a loss of synchronization can cause catastrophic engine damage due to collision between the valves and pistons in engines with a freewheel design, and can also cause damage in engines without a freewheel design.

[0003] The state of the art can be found in DE 38 54 613 T2, US 2014 / 0 287 859 A1 and DE 202 20 527 U1.

[0004] A tensioner typically comprises a base mounted on the motor, an arm that can pivot relative to the base, and a spring that pivotally drives the arm relative to the belt. Damping the movement of the tensioner arm has been found to play an important role in ensuring that the tensioner remains in contact with the belt. Without adequate damping of the tensioner arm, sudden changes in belt tension can result in the arm not following the belt sufficiently, which in turn can lead to the aforementioned loss of belt tension. Various ways of achieving adequate damping have been proposed, but these usually require an expensive tensioner, which is disadvantageous. It would be advantageous to provide a tensioner with sufficient damping while still being cost-effective. Summary

[0005] To solve the problem described above, a clamping device with the features of claim 1 or a clamping device with the features of claim 7 is specified. Further advantageous embodiments are defined in the dependent claims.

[0006] In the following, the term "tension arm" will also be used simply as "arm." The feature of the base shell is used synonymously with "base." The tension spring can be a helical torsion spring and is referred to simply as a "spring" below.

[0007] According to a first aspect as claimed in claim 7, a tensioning device for maintaining the tension of an endless drive member in a belt-in-oil drive system is provided. The tensioning device comprises, among other things: a base having a base shell mountable to a stationary structure and having a peripheral wall defining an arm pivot axis; an arm having a radially inner arm surface and an endless drive member engagement surface engageable with an endless drive member; a sleeve disposed between the radially inner arm surface and the peripheral wall of the base shell; and a tension spring. The arm is held to the base shell by means of the sleeve. The tension spring is arranged to bias the arm in a first direction about the pivot arm axis.

[0008] According to another aspect of claim 1, a tensioning device for maintaining tension in an endless drive member is provided. The tensioning device comprises, among other things: a base having a base shell mountable to a stationary structure and having a peripheral wall defining an arm pivot axis; an arm having a radially outer arm surface and a radially inner arm surface defining a pulley axis parallel to and offset from the arm pivot axis; a sleeve disposed between the radially inner arm surface and the peripheral wall of the base shell; and a tension spring. The arm is held to the base shell by means of the sleeve. The tension spring is arranged to bias the arm in a first direction about the arm pivot axis.The tensioner further comprises a pulley having a radially inner pulley wall rotatably mounted on the radially inner arm surface for rotation about the pulley axis and having a radially outer pulley wall disposed radially outwardly of the base shell and engageable with an endless drive member.

[0009] According to another aspect, a tensioning device for a belt or chain is provided, the tensioning device comprising: a base shell that is stationary relative to the motor; a tension spring; an arm rotatably connected to the stationary base shell via the spring; a bearing installed in an opening in the arm that is eccentric to the radial center of the arm; a pulley for guiding the belt or chain, which is installed or locked to an inner race of the bearing; a sleeve placed between the outer diameter of the arm and the inner diameter of the base shell to provide the thrust surface and a frictional torque. A disc may be provided to act as a thrust surface between the arm and a device enclosing the assembly of the arm, sleeve, spring, and bearing in a chamber in the base shell (e.g., a device on the base shell).The spring resists rotation of the arm / bearing / pulley assembly in a load-stopping direction and forces rotation of the arm / bearing / pulley assembly in a free-arm direction opposite the load-stopping direction. The tensioning device may include a locking device that holds the arm / ball bearing / sleeve / thrust disc / spring assembly within the inner cylinder of the base shell. The locking device is attached to the base shell (press-fitted, swaged, welded, etc.).The tensioner configuration is chosen such that high peaks of fluctuating belt load induced by timing drive components are higher than the tensioner maximum hysteresis torque and low valleys of belt load are lower than the tensioner minimum hysteresis torque, but the combination of the spring torque, the friction torque of the sleeve and pulley (in embodiments where a pulley is present), and the moment of inertia of the tensioner assembly dynamically limits the tensioner arm oscillations to less than approximately + / - 10°.

[0010] According to another aspect, a tensioning device as mentioned above is provided, but wherein the pulley and the bearing are not provided and the arm itself has an engagement surface for direct engagement with the belt or chain. Brief description of the drawings

[0011] The above and other aspects of the invention will become more apparent from the following description with reference to the accompanying drawings. Fig. 1 is a view of an engine with a timing belt drive including a tensioner according to an embodiment of the present invention. Fig. 2 is a sectional view of the clamping device of Fig. 1. Fig. 3 is a plan view of the clamping device of Fig. 2. Fig. 4 is a sectional view of another variant of the clamping device of Fig. 2. Fig. 5 is a sectional view of another variant of the clamping device of Fig. 2. Fig. 6 is a sectional view of an engine with a timing belt drive including a tensioner according to another embodiment of the present invention. Fig. Figure 7 is a view of an engine with a timing belt drive including the tensioner of Fig. 6. Fig. Figure 8 is a sectional view of a variant of the clamping device of Fig. 6. Fig. 9 is a perspective view of the clamping device of Fig. 8. Fig. 10 is another perspective view of the clamping device of Fig. 8 without a pulley. Fig. Figure 11 is a graph showing the relationship between the torque applied by the clamping device and the angular position of the clamping arm. Fig. 12 is a perspective view of a variant of the clamping device of Fig. 8. Detailed description of exemplary embodiments

[0012] The following refers to Fig. 1, which shows a crankshaft 910 of an engine 913 for a vehicle (not shown). Note that the engine 913 is schematically shown as a simple rectangle, however, the engine 913 may have any suitable shape. The vehicle may be any suitable vehicle, such as a car, a truck, a van, a mini-van, a bus, an SUV, a military vehicle, a boat, etc. A timing belt 914 extends between a pulley 912 on a crankshaft 910 of the engine 913 and a pair of pulleys 904a and 904b on camshafts 905a and 905b to transmit rotational power from the crankshaft 910 to the camshafts 905a and 905b.

[0013] A tensioner 100 is mounted on the engine 913 between the crankshaft 910 and the camshaft 905a in embodiments where the timing belt is immersed in an oil bath (hereinafter referred to as a belt-in-oil arrangement). The tensioner 100 maintains the tension of the timing belt 914. An idler is shown at reference numeral 916 on a portion of the timing belt 914 between the camshaft 905b and the crankshaft 910.

[0014] As in Fig. 2, the clamping device 100 includes a base shell 102, an arm 104, a tension spring 106, and a sleeve 108. The base shell 102 may be mounted in any suitable manner such that it is stationary relative to the motor 913 (e.g., by directly mounting it to the motor 913). In one example, the base shell 102 may include a mounting wall 109 having a fastener through-opening 110 through which a clamping device mounting fastener 111 extends, holding the base shell 102 fixedly to the motor 913. The base shell 102 further includes a peripheral wall 112 at a radial periphery of the mounting wall 109. The peripheral wall 112 defines an arm pivot axis Aa.

[0015] The arm 104 includes a radially inner arm surface 114 and an endless drive member engagement surface 116 which is engageable with an endless drive member (e.g., a Fig. 1 shown belt 914 or a chain or any other suitable endless drive link).

[0016] The sleeve 108 is disposed between the radially inner arm surface 114 and the peripheral wall 112 of the base shell 102. The arm 104 is held to the base shell 102 by the sleeve 108.

[0017] The tension spring 106 is arranged to bias the arm 104 in a first direction about the arm pivot axis Aa.

[0018] During operation, the belt 914 is driven by the crankshaft pulley 912 in a selected direction (generally clockwise in the embodiment of Fig. 1). The tension spring 106 urges the arm 104 in a first rotational direction, also referred to as the "free arm direction," and drives the endless drive link engaging surface 116 into the belt 914.

[0019] Damping of this movement is provided by frictional engagement between sleeve 108 and the peripheral wall 112 of base shell 102. The damping torque provided by sleeve 108 is the damping force (i.e., frictional force Fd) multiplied by the moment arm of this force (i.e., the radial distance Dd between the direction line of damping force Fd and the arm pivot axis Aa).

[0020] It should be noted that in some prior art tensioners, the tension arm has a hub and the base shell includes an upwardly extending shaft. The tension arm hub is pivotally supported on the shaft of the base with a sleeve disposed therebetween to provide some damping. The hub, shaft, and sleeve all extend into the interior of the coil torsion spring, with the outer wall of the base shell defining a chamber in which the coil torsion spring is disposed. The damping force is exerted between the shaft and the hub of the arm, and accordingly, the torque resulting from the damping force is relatively small due to the associated relatively small moment arm.

[0021] In contrast, by utilizing the peripheral wall 112 of the base shell 102 to contain the pivoting movement of the arm 104 and positioning the sleeve 108 in association with the peripheral wall 112, the damping force achieved can be greater than that achievable with prior art clamps without significantly increasing the overall surface area of ​​the clamp compared to prior art clamps. In the illustrated embodiment, the sleeve 108 is disposed on the outside of the peripheral wall 112 and provides an even greater torque than if it were disposed on the inside of the wall 112.

[0022] In general, for any tensioner, a long arm length (defined as the distance between the belt engagement surface and the arm pivot axis) increases the torque exerted by the belt on the arm. However, a problem with some prior art tensioners is that it is difficult to create the amount of damping needed to properly control the tensioner's movements during a change in belt tension. If sufficient damping is not provided, the tensioner arm may not adequately follow the belt during a reduction in belt tension, resulting in a loss of belt tension sufficient to cause tooth skipping, which can lead to serious engine damage.To ensure adequate damping relative to the magnitude of the torque acting on the arm from the belt, some tensioner manufacturers keep the arm length relatively small. This limits the magnitude of the torque exerted by the belt on the arm by keeping the arm length (and therefore the moment arm contributing to the torque) small. However, a small arm length is disadvantageous because it implies that a larger angular range of arm movement is required to support a selected amount of movement in the belt. The larger the angular range of arm movement during operation, the greater the change in the geometry of the forces acting on the belt via the tensioner, making it more difficult to approximate an ideal response of the tensioner to changes in belt tension.

[0023] The base may include a cover member 118 that covers the open distal end 120 of the base shell 102 to prevent dust and dirt from entering the clamping device 100.

[0024] The arm 104 may comprise a central portion 119 that rests on a shoulder 123 of the base to axially retain the arm 104 and to set the axial position of the arm 104. The central portion 119 has an opening 121 (see Fig. 3) to receive one end at reference numeral 122 of the helical torsion spring 106. The other end 124 of the spring 106 can extend through an opening in the peripheral wall 112 of the base shell 102. A spring guide wall 126 can extend into the chamber 128 defined by the base shell 102. A fastener access opening 130 in the cover member 118 and an opening 131 in the central portion 119 of the arm 104 allow access to the mounting fastener 111 for assembly and removal of the clamping device 100.

[0025] In the arrangement shown, the damping torque provided by the tensioner 100 depends on the hub load acting on the arm 104. This is because the frictional force exerted between the arm 104, the peripheral wall 112, and the sleeve 108 depends on the normal force between them, which varies with the hub load.

[0026] Fig. Figure 4 shows another embodiment of the clamping device 100. In this embodiment, a shaft 140 is provided as part of the base shell 102. The shaft 140 extends upwardly through the openings 130 and 131 in the cover member 118 of the base and the central portion 119 of the arm 104. The mounting fastener 111 shown can be easily accessed from outside the clamping device 100 to simplify installation and removal of the clamping device 100. A gap is shown between the spring guide wall 126 and the shaft 140 to illustrate that in the illustrated embodiment, there is no frictional engagement between the arm 104 and the shaft 140, which is a distinguishing feature of the clamping device 100 from the prior art.

[0027] Fig. Figure 5 shows another embodiment of the clamping device 100 in which the spring guide wall 126 extends substantially along the entire axial length of the chamber 128 and a spring retainer 150 is provided around the guide wall 126. The spring 106 engages the spring retainer 150 during operation in a manner similar to the engagement between the spring and the spring retainer of Fig. 5 and Fig. 11 of PCT publication WO2014063228A1 to provide damping in addition to the damping on sleeve 108.

[0028] The following refers to Fig. 6, which shows a tensioner 200 according to another embodiment of the present invention. The tensioner 200 is configured for use with non-oil immersed belts (i.e., for dry belt environments). The tensioner 200 includes a base 202, an arm 204, a tension spring 206, a sleeve 208, a pulley 203, and a bearing 205. One difference between the tensioner 200 and the tensioner 100 is that the tensioner 200 includes a pulley and a bearing to allow rotation of the pulley relative to the arm, which is not necessary with the tensioner 100 because it is used in a belt-in-oil environment.

[0029] The base of the second embodiment may be similar to the base of the first embodiment and may have the form of a base shell having a mounting wall 209 with a fastener through-opening 210 for the passage of a mounting fastener 211 that holds the base shell 202 fixed to the motor 913 ( Fig. 7), and a peripheral wall 212 at a radial periphery of the mounting wall 209. The peripheral wall 212 defines an arm pivot axis Aa.

[0030] The arm 204 includes a radially outer arm surface 220 and a radially inner arm surface 222 defining a pulley axis Ap that is parallel and offset from the arm pivot axis Aa. The sleeve 208 is disposed between the radially outer arm surface 220 and the peripheral wall 212 of the base 202. The arm 204 is held in the base 202 by means of the sleeve 208. The pulley 203 includes a radially inner pulley wall 230 rotatably mounted on the radially inner arm surface 222 for rotation about the pulley axis Ap, and a radially outer pulley wall 232 disposed radially outward of the base 202 and connected to an endless drive member (e.g., the belt 914 of Fig. 7). The bearing 205 is arranged between the radially inner arm surface 222 and the radially inner pulley wall 230.

[0031] Tension spring 206 is arranged to bias arm 204 in a first direction (referred to as a free-arm direction) about arm pivot axis Aa to drive pulley 203 into belt 914. In the illustrated embodiment, tension spring 206 is disposed within base 202 in chamber 228 formed therein. Tension spring 206 may be a helical torsion spring similar to spring 106. A first end 240 of spring 206 engages base 202, while a second end 241 of spring 206 engages arm 204.

[0032] In the embodiment of Fig. 6, the radially inner pulley wall 230 defines an axially extending fastener access opening 234 that provides access for installing and removing the fastener 211. As best shown in Fig. 6, the eccentricity of the arm 204 may cause the fastener access opening 234 to be axially offset from the fastener 211 at most arm positions. Therefore, some movement of the arm 204 may be required to align them sufficiently to allow easy access.

[0033] The sleeve 208 in the embodiment of Fig. 6 acts to create a frictional force on the peripheral wall 212 of the base 202 and outside the diameter of the spring 206 to produce a large damping torque compared to the damping torque in some prior art clamping devices in which frictional damping is provided between a hub of the arm and a shaft in the base shell.

[0034] A thrust member 242 is provided at a distal end of the arm 204 and prevents metal-to-metal contact between the arm 204 and the base 202 during operation of the clamping device 200. A locking ring 244 is provided to hold the thrust disk 242 in position.

[0035] Fig. Figure 8 shows a variant of the clamping device 200 in which the base 202 contains a shell 260 which faces the motor 913 with its opening and arms 262 ( Fig. 9) which have openings for mounting the base 202 to the motor 913. The base 202 further comprises a locking ring 264 which is fixed to the locking ring 244 of Fig. 6 opposite axial end of the base 202. The locking ring 264 holds the spring 206 in the chamber in the base 202. Furthermore, a pusher member 242 is provided at a distal end of the arm 204 to prevent metal-to-metal contact between the arm 206 and the base 202.

[0036] In the variant of Fig. 8, the pulley 203 includes an axial end wall 270 extending between the radially inner and radially outer pulley walls 230 and 232, and at least one axial end wall opening. In the example shown, the pulley 203 has four axial end wall openings 272 (see Fig. 9). The pulley 203 can be rotated to an installation position at which the at least one axial end wall opening 272 is aligned with a tool engagement feature 274 (such as a hexagonal opening for receiving an Allen wrench) of the arm 204 and with a first locking pin receiving opening 276 on the base 202, which in turn is aligned with a second locking pin receiving opening 278 on the arm 204. A locking pin 280 can be inserted through the at least one axial end wall opening 272, through one 276 of the first and second locking pin receiving openings, and into the other 278 of the first and second locking pin receiving openings to lock the arm 204 and the base 202 at a selected angular position relative to each other.

[0037] Fig. Figure 10 shows the tensioning device without selected components such as the pulley. As shown in Fig. 10, first and second load-stop interfaces 282 and 284 are provided, respectively, on the base 202 and the arm 204, which cooperate to define a load-stop position for the tensioner 200, which is the position of maximum possible pivoting of the arm resulting from the high tension of the belt 914. First and second free-arm interfaces 286 and 288 are provided, respectively, on the base 202 and the arm 204, which cooperate to define a free-arm position for the tensioner 200, which is the position of maximum allowable pivoting of the arm 204 resulting from the preload force of the spring 206. An alternative configuration for the interfaces 282, 284, 286, and 288 is shown in Fig. 12. In this variant, a pin 291, which is pressed into a tongue extending axially from the arm 204, has interfaces 284 and 288. The pin 291 extends through a slot 293 in the base 202, the ends of which act as interfaces 282 and 286.

[0038] If, as in Fig. 10, the locking pin 280 (which may also be referred to as an installation pin) is installed, the arm 204 is in the load stop position, which keeps the arm 204 out of the way when the tensioner 200 is installed on an engine in which the belt 914 is already installed.

[0039] Fig. Figure 11 shows two hysteresis curves 300 and 302 that represent examples of the torque exerted on the tension arm 204, which drives the pulley 203 into the belt 914. Curve 300 represents the torque on the arm 204 when the friction coefficient on the sleeve 208 is 0.07; and curve 302 represents the torque on the arm 204 when the friction coefficient on the sleeve 208 is 0.15. It should be clear that the upper portions (300a and 302a) of curves 300 and 302 represent the tension arm torque when the arm 204 moves to the load stop position. The lower portions (300b and 302b) represent the tension arm torque when the arm 204 moves to the free arm stop position.

[0040] Hysteresis curves 300 and 302 show that when the friction coefficient increases by a factor of approximately 2, the clamp arm torque remains relatively stable during movement of arm 204 in the free-arm direction, while the torque increases by approximately 50% during movement of arm 204 in the load-stop direction. This is advantageous because, in situations where the friction coefficient is greater than that originally designed for clamp 200, the lower part of the clamp arm torque curve remains stable. In contrast, in some prior art clamps, such as clamps using a spring to apply force to a friction member that contributes to the damping torque, a change in the friction coefficient can result in a large increase in the upper part of the torque curve and also a large decrease in the lower part of the torque curve.

[0041] It is therefore clear that the minimum torque exerted by arm 204 remains relatively stable even with large changes in the coefficient of friction on the damping member (e.g., sleeve 208). The same applies to the minimum torque exerted by arm 104 with large changes in the coefficient of friction on damping member 108. Furthermore, it is clear that the damping magnitude in tensioners 100 and 200 is based on the hub load, as described above. Thus, as the hub load decreases, the damping torque decreases, thereby assisting the action of spring 206 (and 106) to drive arm 204 (or 104) into belt 914.

[0042] By ensuring that the minimum torque exerted by the arm 904 remains relatively stable under many conditions, the risk of a drag effect is reduced, which in turn means that the risk of the tension of the belt 914 dropping to zero, which could lead to tooth skipping and consequent damage to the belt and the motor 913, is reduced.

[0043] It should be noted that the Fig.The tensioner configuration shown in Figures 6-10 offers several advantages. For example, because arm 204 is located outside bearing 205 and pulley 203 rotates on the inside of bearing 205, wear on the bearing is significantly lower because the bearing's rolling elements (e.g., balls) roll at a lower speed than in a case where pulley 203 is located on the outside. The lower speed also results in less heat than in other configurations, which in turn contributes to a longer bearing life.

[0044] And although the arm 204 is disposed outside the bearing 205, the arm 204 is relatively light and occupies relatively little axial space. This is because the arm 204 itself is generally annular, yet there is eccentricity between the inner surface 222 and the outer surface 220. In contrast, the arms of some prior art tensioners can be quite heavy, thereby increasing their inertia and reducing their responsiveness to changes in belt tension. This light weight improves the responsiveness of the arm 204 to changes in belt tension.

[0045] The configuration of arm 204, pulley 203, and base 202 contributes to a relatively small axial height of tensioner 200. It has been found that by sizing chamber 228 with a 6.5 mm space for spring 206 and using an 8 mm wide 6003 ball bearing, the entire tensioner 200 can have an axial height of approximately 21.5 mm and, in some embodiments, can have an eccentricity (i.e., a distance between the pulley axis Ap and the arm pivot axis Aa) of 3 mm and, in other embodiments, 5 mm or more. The damping torque generated at sleeve 208 may be sufficient to support an eccentricity of 25 mm in some cases.

[0046] By providing a greater damping force, the arm length of arm 104 or 204 can be greater than prior art arms, resulting in a relatively smaller angular movement for arm 104 or 204 to support a selected set of belt tensioning conditions. The smaller angular movement of arm 204 allows a "flatter" (i.e., less parabolic) torque curve for spring 206, resulting in generally more constant belt tension during operation of engine 913. The high peaks of belt load induced by belt-engaging components such as crankshaft belt 912 are higher than the maximum torque of any hysteresis curve that may be applied to tensioner 200 (e.g., curve 300); and the low valleys of belt load are lower than the minimum torque of the applicable hysteresis curve to induce movement of arm 204.During operation of motor 913, torques outside the hysteresis curve of tensioner 200 induce movement of arm 204. The combination of spring torque and friction torque (from sleeve 208 and other friction elements such as pusher 242), as well as the inertia of arm 204 and arm-mounted components such as pulley 203 and bearing 205, if present, dynamically limit the oscillations of arm 204 to less than a selected value, such as + / - 10 degrees. In some embodiments, the selected value may be dynamically less than + / - 2 degrees. This advantageously contributes to the flatter torque curve for spring 206 noted above.

[0047] In the embodiments described herein, the arm 104 or 204 can generally be constructed of steel or aluminum. The base can also be constructed of steel or aluminum. The sleeve 108 or 208 can be constructed of nylon, a PTFE-containing material, or PTFE itself, depending on the required damping force and wear resistance.

[0048] Generally, when the sleeve is disposed between the arm and a base to provide damping, the sleeve may be locked against rotation with the arm, thus creating friction with the base, locked at the base, thus creating friction with the arm, or locked at neither of these parts, thus allowing friction to be created with the arm and / or the base. However, in each of these cases, the frictional force is generally provided at the peripheral wall of the base.

[0049] It is clear that the clamping device 200 can be operated without a spring retainer, without a pivot shaft, and without an installation shaft (a shaft for setting a starting position of the arm relative to the base), all of which are relatively expensive components to manufacture, to reduce the manufacturing cost of the clamping device 200. Furthermore, a large damping size is provided even when the diameter of the bearing 205 remains small. The non-bearing-related advantages also apply to the clamping device 100.

[0050] When referring generally to pulley 203 herein, the term "pulley" should be interpreted broadly, including rotating elements with or without teeth configured to engage the smooth side of a toothed belt, the toothed side of a toothed belt, or a chain. The engagement between a pulley and a belt or chain can be either synchronous (i.e., teeth on the pulley engage teeth on the belt or holes in the chain) or asynchronous (the pulley has a smooth engagement surface for engagement with either side of the belt or chain).

[0051] It should be apparent to those skilled in the art that various modifications may be made to the embodiments described herein without departing from the scope of the invention as defined by the following claims. However, the scope of protection is determined by the claims.

Claims

[1] Tensioning device (200) for maintaining the tension of an endless drive member, comprising: a base comprising a base shell (202) which can be mounted stationary relative to a motor and has a peripheral wall (212) defining an arm pivot axis (Aa), an arm (204) having a radially outer arm surface (220) and a radially inner arm surface (222) defining a pulley axis (Ap) parallel to and offset from the arm pivot axis (Aa), a sleeve (208) arranged between the radially outer arm surface (220) and the peripheral wall (212) of the base shell (202), wherein the arm (204) is rotatably held in the base shell (202) by means of the sleeve (208), a pulley (203) having a radially inner pulley wall (230) rotatably mounted on the radially inner arm surface (222) for rotation about the pulley axis (Ap), and having a radially outer pulley wall (232) disposed radially outside the base shell (202) and engageable with an endless drive member, and a tension spring (206) arranged to bias the arm (204) in a first direction about the arm pivot axis (Aa), characterized by in that a mounting wall (209) of the base shell (202) has a fastener through-opening (210) for receiving a mounting fastener (211), and wherein the radially inner pulley wall (230) defines an axially extending central opening (234) providing access to the fastener through-opening (210). [2] Tensioning device (200) according to claim 1, wherein the tension spring (206) is arranged in the base shell (202). [3] Tensioning device (200) according to claim 1 or 2, wherein the tension spring (206) is a helical torsion spring. [4] A clamping device according to any one of the preceding claims, wherein the arm (204) is generally annular. [5] A tensioning device according to any one of the preceding claims, wherein the sleeve (208) provides a damping torque which depends on a force exerted on the arm (204) by the endless drive member. [6] A tensioning device according to any one of the preceding claims, wherein the damping torque provided by the arm (204) is such that an increase in the coefficient of friction on the sleeve (208) results in a drop of less than 25 percent of a minimum torque exerted by the tensioning arm (204) on the endless drive member during operation. [7] A tensioning device (100) for maintaining the tension of an endless drive member in a belt-in-oil drive system, comprising: a base comprising a base shell (102) which can be mounted stationary relative to the motor and has a peripheral wall (112) defining an arm pivot axis (Aa), an arm (104) having a radially inner arm surface (114) and an endless drive member engagement surface engageable with an endless drive member, a sleeve (108) arranged between the radially inner arm surface (114) and the peripheral wall (112) of the base shell (102), the arm (104) being rotatably held on the base shell (102) by means of the sleeve (108), and a tension spring (106) arranged to bias the arm (104) in a first direction about the arm pivot axis (Aa), wherein a mounting wall of the base shell (102) has a fastener through-opening (110) for receiving a mounting fastener (111), and wherein the clamping device (100) has a cover member (118) covering an open end of the base shell (102) and defining an axially extending fastener access opening (130) providing access to the fastener through-opening (110). [8] The tensioning device (200) of any one of claims 1 to 6, further comprising a bearing (205) between the radially inner arm surface (222) and the radially inner pulley wall (230). [9] Tensioning device (100) according to claim 7, wherein the tension spring (106) is a helical torsion spring. [10] A tensioning device (200) according to any one of claims 1 to 6 or 8, wherein the pulley (203) comprises an axial end wall (270) extending between the radially inner and radially outer pulley walls (230, 232) and at least one axial end wall opening (272), wherein the pulley (203) can be rotated to an installation position at which the at least one axial end wall opening (272) is aligned with a tool engagement means (274) of the arm (204) and with a first locking pin receiving opening (276) on the base shell (202), which in turn is aligned with a second locking pin receiving opening (278) on the arm (204), and wherein the tensioning device (200) further comprises a locking pin (280) extending through the at least one axial end wall opening (272), through one of the first and second locking pin receiving openings (276, 278) and into the other of the first and second locking pin receiving openings (276, 278),to lock the arm (204) and the base shell (202) at a selected angular position relative to each other., [11] A tensioning device (100) according to any one of claims 7 or 9, wherein the sleeve provides a damping torque that depends on a force exerted on the arm (104) by the endless drive member (108). [12] A tensioning device (100) according to any one of claims 7, 9 or 11, wherein the damping torque provided by the arm (104) is such that an increase in the coefficient of friction on the sleeve (108) results in a drop of less than 25 percent of a minimum torque exerted by the tensioning arm (104) on the endless drive member during operation.

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