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How Important is Spring Technology?

BULLETIN NO. 433-0824 • DATE 11-2001

Spacing between the coils of a roundspring tensioner eliminates metal-to-metal contact, flex fatigue failure,noise, and contamination, whichoften causes a flat spring to “lockup” or seize the tensioner.

Flat spring designs trap dirt andgrit between the coils. Thesecontaminants wear away the Teflonseparator tape and can seize thetensioner. Rust is often an earlyindication that the tensioner needsto be replaced.

Heavy duty automatic belt tensioners are designedto absorb accessory drive vibrations that lead toexcessive belt wear and noise problems.

How does a belt tensioner reduce vibrations? Oneof the solutions is in the spring technology.

Aftermarket tensioners are available with eitherflat or round springs. Theoretically, the flat springis just as effective in providing a constant force as around spring.

Mechanically, however, there are major differencesthat affect performance and service life.

Fatigue failure: Flat springs have more stresspoints along the spring edges that can weaken andcrack, and lead to fatigue failure. Round springshave no stress points because spaces between thecoils eliminate metal-to-metal contact. They arealso quieter.

Contamination: Flat spring design is subject tofailure due to contamination when dirt and gritbecome trapped between the coils. The flat springwill eventually “lock up” or seize, resulting in lossof tension for the drive system. Round springs arenot affected by contamination because of thespacing between the coils.

Coil interference: The coils of a close-wrapped,flat spring rub against each other as they vibrate.This increases heat build-up which leads tocomponent wear and failure. Flat spring tensionersuse Teflon® tape as a lubricant to reduce frictionbetween coil surfaces. However, heat, friction andcontamination erode the tape over time. Roundsprings have no coil-to-coil contact. There is nofriction and no noise.

How Does A Damping MechanismIncrease Tensioner and Belt Service Life?

Gates patented damping mechanism

Heavy duty serpentine belt drive systems on dieselengines are subjected to violent pulsations andextreme shock loads.

Typical causes are on/off fan clutch systems thatabruptly start and stop, high output generators,accessory loads and engine startup and shutdown.

To reduce tensioner vibration and belt drivestability problems, Gates has developed a robustand patented damping system.

Gates Green Stripe® DriveAlign® automatic belttensioner is designed to resist extreme vibrationswhile providing stable damping.

During peak-to-peak vibration tests equivalent to400,000 road miles, the tensioner withstoodtorsional spikes at 20 cycles/second for three timeslonger than other aftermarket products.

The tensioner’s ability to absorb extreme vibrationmeans that it has high damping levels so thattensioner motion, and fatigue of the inner roundspring are reduced.

Here’s how it works. The damping mechanismfunctions like a shock absorber. The torsionalspring applies constant pressure to the dampingmechanism, which diminishes the oscillation of thetensioner arm.

Reducing the tensioner arm motion provides properbelt alignment and tension for improved driveefficiency and service life of all the drivecomponents, including bearings and pulleys. Thedamping mechanism also reduces belt vibration - orflutter - that is typical with diesel engines.

The end result is that Gates trouble-free DriveAligntensioners reduce accessory drive maintenance.

BULLETIN NO. 433-0826 • DATE 11-2001