CA2593116C - Tensioner assembly with electronically controlled vibration clutch assembly - Google Patents

Abstract

A tensioner for use in a belt or chain drive system includes a base and a tensioner arm pivotally mounted to the base and movable between a load stop position and a free stop position. A spring biases the tensioner arm to move towards the free arm stop position. A clutch spring is associated with the base and tensioner arm. An electronic actuator, preferably an actuator comprising a shape memory alloy, is associated with the clutch spring for engaging and disengaging the clutch spring in relation to the base, whereby a stop position of the tensioner arm can be selectively fixed upon selective activation of the electronic actuator.

Description

TENSIONER ASSEMBLY WITH ELECTRONICALLY CONTROLLED
VIBRATION CLUTCH ASSEMBLY
Field of the Invention [0001] The invention relates to tensioners for belt drive systems, and more particularly to tensioners for belt drive systems capable of actuation to various positions.
Description of the Related Art

[0002] Typical belt tensioners are known in the art for use in automotive applications and are utilized to apply a steady uniform load to the belt or chain to maintain the applied belt tension on a slack slide of the belt drive above a minimum value required to drive various components attached to the belt system. Additionally, belt tensioners are utilized in a non-synchronized belt drive system to prevent belt slippage and power transmission loss.
Tensioners are commonly utilized in accessory drive systems, and timing belt or timing chain systems of an automobile.

[0003] Typical belt tensioners include a tensioner arm, which is fitted with an idler pulley that is applied to the belt. A radial bearing operably connects the idler pulley to the tensioner arm. The tensioner arm is rotatably mounted on a pivot pin that is fixedly mounted to the engine. The axis of rotation of the idler pulley is offset from the axis of rotation of the tensioner arm. A bushing is disposed about the pivot pin. A rotary spring is wrapped coaxially around the bearing pin and bushing for pretensioning the tensioner arm enabling the idler pulley to exert a predetermined force on the belt. In this manner, the force of the rotary spring applies a load to the belt to take up slack due to changes in the length of the belt or chain.

[0004] In a typical belt drive system, a primary drive pulley, such as an engine crankshaft pulley rotates to drive various accessory components associated with the belt system, for example, an alternator, water pump, power steering pump or air conditioning compressor. As the belt stretches under load, the coil spring must drive the tensioner arm farther into the belt to compensate for the longer belt length.

[0005] Variations in the belt tension occur when the driving pulley suddenly decelerates from a steady state condition while the other components continue rotating due to their own inherent inertia. In this situation, the accessory components become the primary drivers within the system resulting in changes in the tension within the belt. During this transitional REV A

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maximum travel position. This backward motion continues to a point corresponding to the tensioner arm position at which the torque output applied by the coil springs inside the tensioner equals or exceeds the equivalent load applied to the tensioner arm by the belt span.
If the torque output of the spring is significantly lower than the load applied by the belt span, the tensioner arm continues to travel until it reaches its mechanical load stop, possibly overstressing the coil spring inside the tensioner. Additionally, fluctuations in the tension within the belt can lead to belt flutter or belt skip resulting in damage to the other components of the belt drive system.
[0006] A tensioner has been proposed in WO 03/048606 wherein a clutch spring and a frictional brake are utilized to provide a travel limit for the tensioner arm.
This tensioner has a relatively large range of travel to take up a significant degree of belt flutter. However, the tensioner passively responds to belt movement to enable the braking or locking function.

[0007] Another tensioner is commercially available on an Alfa Romero 3.01 24 valve engine.
This tensioner provides a clutch spring that is operably connected between a bi-metallic strip and a tensioner arm. As the.temperature varies, the length of the strip varies proportionally.
This movement is coupled to the clutch spring to engage and disengage the spring. As the engine temperature increases, the clutch spring allows a greater degree of travel of the tensioner arm to take up the slack in the belt as it stretches with increasing temperature. The tensioner passively responds temperature to effect the braking or locking function.

[0008] There is therefore a need in the art for a tensioner capable of dynamic actuation or adjustment to various positions in response to transitional loading in the belt drive system, providing stability to the belt drive system.
Summary Of The Invention

[0009] A tensioner for use in a belt or chain drive system includes a base and a tensioner arm pivotally mounted to the base and movable between a load stop position and a free stop position. A spring biases the tensioner arm to move towards the free arm stop position. A
clutch spring is associated with the base and tensioner arm. An electronic actuator, preferably an actuator comprising a shape memory alloy, is associated with the clutch spring for engaging and disengaging the clutch spring in relation to the base, whereby a stop position of the tensioner arm can be selectively fixed upon selective activation of the electronic actuator.

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Brief Description Of The Drawings

[0010] Figure 1 is schematic representation of an accessory drive system including alternator and air conditioning pulleys;

[0011] Figure 2 is a perspective assembly view of a first embodiment of a tensioner having an electronic actuator;

[0012] Figure 3 is a perspective view of a first embodiment of a tensioner having an electronic actuator;

[0013] Figure 4 are side views detailing the tensioner of the first embodiment in various positions;

[0014] Figure 5 is a schematic representation of an accessory drive system including an alternator that is utilized as a starter for an engine;

[0015] Figure 6 is a schematic representation of the accessory drive system when the alternator is starting the engine resulting in a reversal of the tension within the belt;

[0016] Figure 7 is a side sectional view a second embodiment of a tensioner having an electronic actuator;

[0017] Figure 8 is a side sectional view of a third embodiment of a tensioner having an electronic actuator;

[0018] Figure 9 is a perspective view of a fourth embodiment of a tensioner having an electronic actuator;

[0019] Figure 10 is a perspective view of a fifth embodiment of a tensioner having an electronic actuator;

[0020] Figure 11 is a side sectional view of the clutch mechanism of the electronic actuator according to the embodiment disclosed in Figure 10;

[0021] Figure 12 is a schematic representation of a open loop control of the tensioner of the present invention;

[0022] Figure 13 is a schematic representation of a closed loop control of the tensioner of the present invention;

[0023] Figure 14 is a perspective view of a fifth embodiment of the tensioner of the present invention; and

[0024] Figure 15 is a side elevational view of a sixth embodiment of the present invention.

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Detailed Description Of The Preferred Embodiments

[0025] Referring to Figure 1, there is shown a schematic representation of an accessory drive system 2 including a crankshaft pulley 5, alternator pulley 10, air conditioner pulley 15, and a tensioner 20 disposed between the crankshaft pulley 5 and alternator pulley 10. A belt 17 is wrapped about the pulleys for transferring rotational force between the pulleys. Such a representation is generic with respect to an accessory drive and may include other components commonly associated with accessory drive systems of automobiles.

[0026] As can be seen in Figure 1, the tensioner 20 is rotatable about a first axis of rotation from a free arm stop position 25 corresponding to the maximum inward position with respect .
to the belt 17. The tensioner 20 also includes a load stop position 30 at the opposite extreme of the tensioner travel denoting the maximum position the tensioner may move away with respect to the belt 17. Between the two extremes of the free arm stop 25 and load stop 30 positions is a nominal belt position 35 indicating the position of the tensioner 20 with respect to the belt 17 under steady state conditions.

[0027] Referring to Figures 2 and 3, there is shown a first embodiment of a tensioner 220 = having an electronic actuator 210, preferably a shape memory alloy actuator, according to the present invention. As can be seen, the tensioner 220 includes a body or base 205 having a circular ring or drum portion 215 extending there from. A spindle or pivot shaft 225 extends from the base 205 centrally or coaxially within the drum 215. A tensioner arm 230 and bushing 235 are disposed about the pivot shaft 225 and include a tensioner spring 240 disposed between the spring support 235 and tensioner arm 230. A clutch spring 245 is = staked or attached to the tensioner arm 230 at a first end 247 of the clutch spring 245 and retained by the drum 215 at a second end 249 of the clutch spring 245. The clutch spring 245 is disposed about the shaft 225 and drum 215. An inner surface 255 of the clutch spring 245 may engage an outer surface 260 of the drum 215 to prevent movement of the tensioner 220 by locking it in a desired position.

[0028] A pulley 265 is rotatably mounted about tensioner arm 230 and engages the belt or chain of a belt system. Pulley 265 rotates about a second axis that is parallel to and offset from the first axis of rotation of the tensioner arm 230.

[0029] Attached to the body or base 205 is a T-shaped pivot member or arm 270 disposed about a pivot pin 275 for pivotal movement between an engaged position and a disengaged position. The second end 249 of the clutch spring 245 is attached or staked to ,a first branch 277 of the pivot member 270. A return spring 257 is attached to a second branch 279 of the REV A

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arm 270 for biasing the clutch spring 245 to a disengaged position relative to the drum 215, as will be discussed in more detail below. A third branch 281 of the arm 270 includes the electronic actuator 210 of the present invention. The electronic actuator 210 comprises a shape memory alloy wire 212 attached at a first end 214 to the third branch 281 of the arm 270 and a second end 216 attached to the body portion 205 of the tensioner 220.

[0030] The shape memory alloy wire 212 contracts or lengthens in response to a change in temperature. In a preferred aspect, the shape memory alloy wire 212 contracts in response to a change in temperature. In a preferred aspect, a current may be applied to the shape memory alloy wire 212 rapidly raising the temperature of the wire 212 causing actuation or movement of the Arm 270 about the pivot pin 275. In this manner, the second end 249 of the clutch spring 245 is manipulated to cause engagement of the inner surface 255 of the clutch spring 245 with the outer surface 260 of the drum 215. The coils or wraps of the clutch spring contract increasing frictional engagement thereby, preventing movement of the tensioner 220 and locking it in a desired position.

[0031] Also included in the first embodiment is a stop or pin 285 positioned adjacent to the arm 270 preventing movement of the arm 270 beyond a desired position.

[0032] In a preferred aspect of the present invention, the shape memory alloy wire 212 may comprise nitinol or flexinol SMA materials. Typical SMA materials contract or expand when undergoing a phase transformation, resulting in a length change of from 4 to 10 percent at the transition temperature of the SMA material. However, a specified wire 212 of a given composition and shape can contract or expand to a specified distance within tight tolerance controls. Preferably, flexinol is utilized by the present invention as it has advantageous fatigue properties allowing for greater numbers of cycles to be performed before failure of a wire. Preferably, the flexinol wire does not undergo a phase change causing contraction of the wire below a temperature of 200 C. In this manner, the wire 212 will not be affected by ambient temperature changes under the hood of an engine compartment.

[0033] While the electronic actuator. 210 has been described as comprising an element of wire, it is to be understood that other elements such as strips, bars, or tubes may also be utilized by the present invention. The temperature of the shape memory alloy wire 212 can be kept within a designated range to prevent overheating of the wire 212.

[0034] A hall effect sensor (not shown) may be positioned proximate the shape memory alloy wire 212 to monitor the current within the wire 212. The current can be associated with a temperature, such that adjustment of the current will maintain the temperature within a REV A

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desired range. The hall effect sensor may be integrated with a connector associated with the shape memory alloy wire 212 or positioned in proximity to the wire 212.
[00351 Referring to Figure 4, in operation, the tensioner 220, as shown in Figure 4a, is generally in an open or movable position in which the clutch spring 245 does not contact the outer surface 260 of the drum 215 significantly allowing the tensioner 220 to move and operate in a normal condition, as shown in Figure 4b. In Figures 4a and b, the return spring 257 biases the clutch spring 245 to the open position. Referring to Figure 4c, when the electronic actuator 210 is engaged by applying a current from an energy source, preferably through a controller, the wire 212 contracts, pivoting the arm 270 about its pivot pin 275 against the biasing force of the return spring 257. The second end 249 of the clutch wire 212 is then moved, contracting the coils of the clutch spring 245 to engage the outer surface 260 of the drum 215. When the clutch spring 245 engages the outer surface 260, the tensioner 220 is locked to prevent movement of the tensioner 220 away from or towards a belt or chain in a drive system.
100361 The element of shape memory alloy wire 212 of actuator 210 may be controlled by various techniques, including open and closed loop systems, shown in Figures 12 and 13, respectively. One property of the electronic actuator 210 advantageous for rapid control is its rapid response to a signal input comprising an electrical current, thereby rapidly changing the length of the wire 212. In this manner, the electronic actuator 210 acts as a digital on/off switch, as opposed to an analog switch, which changes over time in response to an input.
100371 The electronic actuator 210 may be controlled by open loop mapping various conditions of known instability in the belt system, by an engine control unit 231. For example, various conditions can be monitored within an engine, such as engine speed (RPM) that would trigger application of a current to the shape memory alloy wire 212. Other conditions present in the components of the belt system can also be monitored and utilized as an indication that impending resonance or instabilities are present or about to occur, thereby, triggering the electronic actuator 210. In this manner, a system can be analyzed to preprogram actuation of the electronic actuator, when certain conditions exist.
[0038] Alternatively, a position sensor 232 may be utilized to determine a position of the tensioner arm. By monitoring the relative position of the tensioner arm 230, an engine control unit 231 can determine when oscillations are sufficient to justify activation of the electronic actuator 210 to lock the tensioner arm 230 in position. A feedback loop including the positional sensor incorporated above and the electronic actuator 210 can provide for real = 703556CA
time adjustment of the position of the tensioner 220 such that the tensioner 220 can be locked and unlocked in response to various parameters.
[00391 Referring to Figures 7 and 8, there are shown second and third embodiments of the tensioner similar to that of the first embodiment. The second and third embodiments also utilize an element of shape memory alloy wire 212 with various minor differences. In Figure 7, the shape memory alloy wire 212 is wound around a pivot 300 prior to attachment to the pawl or arm 270. In this manner, various mechanical advantages and layouts can be accommodated. Also, in Figure 5, the return spring 257 is replaced with a spring clip 305 for biasing the arm 270 to maintain the clutch spring 245 in an open position.
While the preferred embodiments of the tensioner have been described as having the clutch spring 245 in the open position under steady state conditions, the clutch spring could be locked under normal conditions such that the shape memory alloy actuator 210 must be triggered to disengage the clutch spring 245 allowing movement of the tensioner with respect to the belt.
100401 With reference to Figure 8, the shape memory alloy wire 212 is shown pivoting about a different pivot point 300 than the second embodiment of Figure 7 prior to engagement with the arm 270. The return spring of the third embodiment is a clock spring 310 as opposed to the coil spring 257 and spring clip 305 of the first and second embodiments.
100411 Figure 9 details a fourth embodiment of the present invention, in which the electronic actuator 210 comprises the tensioner spring 240'. In this embodiment, the tensioner spring 240' is made out of a shape memory alloy material, which contracts in response to a change in temperature, preferably caused, by a current passed through the wire. In this embodiment, the tensioner spring 240' can change its overall length to engage the bushing 235 thereby preventing movement of the tensioner 220 with respect to a belt drive system.
Alternatively, the clutch spring 245, as shown in Figure 4, may be made of a shape memory alloy material, such that the length of the clutch spring can be changed upon the application of current to the wire 212.
[0042] Referring to Figures 10, 11 and 14, there is shown a fifth embodiment of a tensioner 520 having an electronic actuator, preferably a shape memory alloy actuator 510, of the present invention. A pivot member 505 is rotatably mounted and has a tab 507 extending there from is disposed about a shaft 525. The electronic actuator 510 comprises a shape memory alloy wire 512 wrapped around the rotational member 505, such that application of a current over the wire directly moves the rotational member 505 to various positions. A clutch spring 545 is associated with the tab 509 of the rotational member 505.
Movement of the rotational member 505 causes the tab 509 to interact with the clutch spring 545 to engage and = 703556CA
disengage the clutch spring 545, as previously described with respect to the first embodiment.
Another tab 507 is attached to the rotational member for preventing movement of the tensioner beyond a desired distance. A return spring 537 comprising a clock spring biases the rotational member 505 such that the clutch spring 545 is biased towards an open position.
100431 In this embodiment, the shape memory alloy wire 512 contracts, shortening its overall length, causing rotation of the rotational member 505, which in turn causes movement of the clutch spring 545 to lock the tensioner 520 in a desired position. The rotational member 505 may include screws or channels 550 formed on the outer surface 555 of the rotational member 505. The shape memory alloy wire 512 is disposed within the channel 550 and wrapped around the rotational member 505 providing additional engagement of the wire 512 with the outer surface 555 of rotational member 505, as well as preventing damage to the wire 512.
[00441 Referring to Figure 15, a sixth embodiment of the present invention is illustrated. In this embodiment, the electronic actuator 610 is preferably a solenoid, the length of which can be selectively controlled by applying predetermined amounts of electricity.
100451 Through the use of an electronic actuator, the tensioner 20 can be selectively fixed or locked to any position between the free arm stop 25 and load stop positions 30 and locked into position. By locking the tensioner 20 in a specific position, the tensioner 20 would act as fixed idler pulley providing a set tension to the belt 17 of the belt drive system 2. The fixed position allows the belt drive system 2 to maintain stability during transitional periods produced by oscillations in belt tension.
100461 In another aspect of the present invention, a tensioner 20 having an electronic actuator may be utilized in a belt drive system using an alternator as a starter for an engine. In this application, as shown in Figure 5, the accessory drive system may be utilized as a starter for an engine, negating the need for a separate starter motor. As can be seen in Figure 5, the accessory drive system 102 includes a crankshaft pulley 105, a starter /alternator pulley 110, a power steering pulley 115, an idler pulley 122, and an air conditioner pulley 125. A belt 117 is positioned around the pulleys for transferring torque from the crankshaft pulley 105 to the accessory pulleys. A belt tensioner 120 is positioned on the slack side 140 of the belt 117 between the starter/alternator 110 and crankshaft 105 pulleys. The belt tensioner 120 is movable from a free arm stop position 145 to a load stop 150 position. Under normal operation, the crankshaft pulley 105 operates as the driving member of the accessory drive system 102 providing torque to the various accessory pulleys. During normal operation, the tight side 142 of the belt 117 is positioned between the air compressor pulley 125 and ' =
crankshaft pulley 105 with a slack side 140 of the belt 117 being positioned between the alternator/starter 110 and the crankshaft 105 pulleys. However, when the alternator is utilized as a starter, as shown in Figure 6, the alternator pulley 110 would become the primary drive pulley resulting in a reversal of the tension within the belt spans wherein the span between the crankshaft 105 and alternator/starter 110 pulleys would become the tight sPan 142 and the span between the alternator/starter 110 and power steering 115 pulleys would become the slack span 140. Under such a load condition, the tensioner 120 would normally move in a direction away from the belt 117 towards its load stop position 150.
However, through the use of an electronic actuator, the belt tensioner 120 can be adjusted or locked in position towards its free stop position 145 to provide a constant tension on the belt 117 to prevent slack in the belt from causing oscillations within the system or uncontrolled belt slippage and belt traction loss, potentially causing damage to the system. In this manner, the belt tensioner 120 provides stability to the system against oscillations and belt slippage generated by the reversal of the tight and slack spans. In a preferred aspect of the present invention, the tensioner 120 will move towards the free arm stop position 145 prior to engaging the alternator/starter assuring maintenance of sufficient belt tension to absorb belt stretch and torsional oscillations within the system. Once the engine has started running, the tensioner is released and allowed to operate normally.
10047] A tensioner 20 having an electronic actuator may also be utilized by the present invention as an anti-belt tooth skip mechanism. Belt tooth skip typically occurs when a belt or chain of a belt system becomes too long for the drive system, allowing the tooth profile of the belt or chain to rise to a sufficient height to escape the corresponding pocket or recess within the sprocket or pulley designed to hold the belt captive. Under normal operating conditions, the function of a tensioner 20 of a timing belt or timing chain system is to apply sufficient load to a slack side of the belt or chain so as to prevent rise of the belt teeth above a certain threshold of the tooth profile of the sprocket or pulley. However, in situations where the belt rises above the profile, belt tooth skip can occur such that the belt or chain loses grip and skips backward a tooth on the drive pulley relative to its correct position. In such a situation, severe damage to various components can occur. Again, a tensioner 20 having an electronic actuator can be utilized to move the tensioner 20 with respect to the belt or otherwise lock the tensioner 20 into position thereby taking up the slack within a belt or chain to prevent belt tooth skip.
[0048] In another aspect of the present invention, a tensioner 20 having an electronic actuator, preferably a shape memory alloy actuator, can be utilized to prevent ratcheting = 703556CA
. .
within a tensioner 20. Accessory drive tensioners and timing belt tensioners are often equipped with pneumatic or hydraulic dampers or springs to provide resistance to tensioner arm motion when the tensioner arm is forced away from the belt during high periods of torsional activity and system inertia. Pneumatic and hydraulic dampers generally dissipate significantly more energy than frictional tensioners. The primary disadvantage of pneumatic and hydraulic tensioners, however, is their tendency to get permanently "pumped up" over time as they are forced in a direction away from the belt, in response to transitional loads within the belt span. As the tensioner load "pumps up", or ratchets upward, the resulting tension applied to the belt increases as a result. As a result of the increased tension, the applied load to the various components within the system increases reducing the overall life of the belt, as well as pulleys, bearings, and other mechanisms within the system. However, the increased belt tension can be utilized to provide stability to the system under transitional loads. Again, a tensioner 20 having an electronic actuator could be utilized to adjust the tensioner 20 or lock the tensioner 20 in a fixed position preventing movement away from the belt. Such an adjustment would allow for movement of the tensioner arm towards the free arm position into the belt in response to various belt inputs, but would prevent movement of the tensioner arm away from the belt. In this manner, the tensioner having the electronic actuator allows the tensioner to take advantage of the high belt loads induced by the natural ratcheting action of the tensioner arm against the locked position. However, unlike prior art tensioners, the higher belt loads can be released upon command by an engine control computer to prevent buildup of applied tension within the belt when a higher belt system tension is no longer required to provide stability to the system in response to a disturbance or period of high torsional activity.

Claims (17)

Claims:

1. A tensioner for use in a belt or chain drive system comprising:
a base;
a tensioner arm pivotally mounted on the base, said tensioner arm movable between load stop position and a free stop position;
a tensioner spring biasing said tensioner arm to move towards the free stop position;
a pulley rotatably mounted on said tensioner arm, said pulley having an axis of rotation offset from an axis of rotation of said tensioner arm;
a clutch spring associated with the base and connected to said tensioner arm;
an electronic actuator associated with the clutch spring for engaging and disengaging the clutch spring, whereby the tensioner arm is selectively fixed in response to electrical inputs to said electronic actuator.

2. A tensioner as set forth in claim 1, said base has a drum and said clutch spring is wrapped about said drum.

3. A tensioner as set forth in claim 2, wherein said tensioner further comprises a pivot member pivotally mounted on said base, said pivot member extending between said clutch spring and said electronic actuator.

4. A tensioner as set forth in claim 3, wherein said pivot member is biased to urge said clutch spring to disengage from said drum.

5. A tensioner as set forth in claim 4, wherein when said clutch spring is disengaged, said clutch spring is urged to unwrap from said drum enabling free movement of said tensioner arm and when said clutch spring is engaged, said clutch spring is urged to wrap about said drum, limiting movement of said tensioner arm.

6. A tensioner as set forth in claim 1, wherein said electronic actuator comprises an element of shape memory alloy.

7. A tensioner as set forth in claim 6, wherein said element is selected from a group comprising: wire, strip, bar and tube.

8. A tensioner as set forth in claim 6, wherein said shape memory alloy is nitinol or flexinol.

9. A tensioner as set forth in claim 1, wherein said electronic actuator is a solenoid.

10. A tensioner as set forth in claim 1, further comprising, a controller configured to generate said electrical inputs for said electronic actuator to activate and deactivate said electronic actuator.

11. A tensioner as set forth in claim 10, wherein said electrical inputs are responsive to predetermined engine conditions.

17. A tensioner as set forth in claim 11, wherein said engine conditions are selected from a group comprising: engine speed, accessory drive component status, vehicle gear selection, and tensioner arm position.

13. A tensioner for use in a belt or chain drive system comprising:
a base;
a tensioner arm pivotally mounted on the base, said tensioner arm movable between load stop position and a free stop position;
a tensioner spring biasing said tensioner arm to move towards the free stop position;
and a pulley rotatably mounted on said tensioner arm, said pulley having an axis of rotation offset from an axis of rotation of said tensioner arm;
whereby said tensioner spring is made of a shape memory alloy responsive to electrical inputs to selectively fix said tensioner arm in place.

14. A tensioner as set forth in claim 13, further comprising a controller configured to generate said electrical inputs for said tensioner spring.

15. A tensioner as set forth in claim 14, wherein said electrical inputs are responsive to predetermined engine conditions.

16. A tensioner as set forth in claim 15, wherein said engine conditions are selected from a group comprising: engine speed, accessory drive component status, vehicle gear selection, and tensioner arm position.

17. A method of starting an engine having a starter/generator coupled to the engine by an endless drive belt and an electronic tensioner engaging said belt maintaining a desired amount of tension in said belt, comprising the steps of:
providing an electrical input to said electronic tensioner to lock said electronic tensioner to provide a constant tension on the belt;
providing an electrical input to said starter/generator to drive the endless belt; and releasing said electronic tensioner once the engine has started running.