More and more vehicles are rolling off the assembly line equipped with clutch and decoupler pulleys threaded on their alternators. There’s a good reason for that.
Today’s generation of high-output alternators place tremendous stress on the entire accessory drive system. Those alternators are also being mated to growing numbers of rough-idling, four-cylinder and diesel engines that exert even greater belt-speed changes on the entire system. And if that weren’t enough, car companies are decreasing engine idle speeds in order to increase fuel economy, which just adds more vibration and belt speed fluctuations to the mix. The end result? A whole lot of screeching, stretching, slipping and broken belts, dead batteries, and water pump and power-steering bearings that break down much too soon. Clutch, and particularly decoupler pulleys, go a long way to calming those vibrating tensioners and reducing drive belt wear and tear… but we’ve gone one better.
The CT Drives pulley is a patent pending system that provides the same benefits as both clutch and decoupler pulleys in a much simpler and more reliable design.
What’s more, the CT Drives Pulley is the only product on the market you can use as a direct swap and replacement for both clutch and decoupler pulleys.
Clutch and decoupler pulleys overrun or “freewheel” when the engine decelerates; this reduces strain on the drive belt. The downside is that this uncontrolled freewheeling also sends needle bearings in a clutch pulley spinning to extreme RPMs. The result? Excessive friction, heat and premature failure of rollers and springs.
Above: Extensive testing proves that the CT Drives pulley provides the same belt-calming benefits as a decoupler pulley in a simpler more reliable design.
Our research and testing prove that one can quiet belt-chirps and cancel out damaging speed fluctuations between the drive belt and alternator with a precise degree of overrun. In essence, the CT Drives pulley features just the right amount of overrun—enough to stop vibrations and reduce belt wear, but not enough to cause the worn bearings and springs you see in conventional clutch and decoupler pulleys.
Clutch pulleys do not accommodate abrupt increases in speed, as when combustion occurs, since they engage suddenly and attempt to accelerate the shaft rotation rapidly to match the increased belt velocity from each piston-firing event. Such repeated sudden engagement of the clutch with the pulley results in tensioner bounce, noise, high wear, and frequent failures, not only of the clutch itself, but also of the load surges on the FEAD (Front Engine Accessory Drive) component bearings and stretching serpentine belts.
The clutch mechanism in a starter drive, which is essentially what you find inside clutch pulleys, is designed to crank an engine for less than 5 seconds, then overrun freely for about another 5 seconds, then cool off for at least 20 seconds before the cycle re-starts. Even OE-caliber drive clutches are only expected to withstand this cycle about 50,000 times before failing.
Yet an alternator clutch pulley locks and releases 3 times per engine revolution at idle, or about 144,000 times per hour...with no rest period. When you compare these simple numbers, it becomes painfully obvious why clutch pulleys don’t last.
When they were introduced to the market, decoupler pulleys were a big step forward—they used a spring and friction-clutch mechanism to attenuate engine excitation frequencies. This system isolates the alternator from the drive belt and significantly reduces noise, vibration and wear.
In short, it was a good mouse trap, but we’ve made a better, more reliable one. It starts with our proprietary spring system.
Above: CT Drives springs are pulse-tuned for specific applications and engineered for extreme durability.
Conventional decouplers use a friction clutch and a steel coil spring, which have a tendency to failure from invisible fatigue cracks, corrosion, and heat stresses due to grease loss. We achieve the same belt and tensioner calming effects by using a simpler, proprietary and custom-formulated, high-temperature material spring. CT Drives springs never deform and can withstand continuous 130°C under hood temperatures with no lubrication and no loss in performance whatsoever.
The CT Drives springs and the alternator rotor comprise a spring - mass system which does have a resonant frequency. Yet, like decouplers, we designed our springs so that their resonant frequency is less than engine idle speed. So, in operation, the CT Drives pulley passes momentarily through resonance during the first partial revolution of the engine while it is being started, but never while the engine is running.
Like conventional decouplers, our springs are tuned for four, six and eight-cylinder applications and are, in a word, bullet proof.
Should the bearing in a CT Drives pulley actually fail, the pulley will still continue to transfer full torque so the alternator will charge the battery. No other product on the market can do the same. And when it comes time to eventually rebuild an alternator with a CT Drives pulley, servicing our pulley is as quick and simple as pressing out the end cap and replacing the springs. The CT Drives pulley is, hands-down, the easiest product of its kind to work with.
The CT Drives design is so effective and flexible that it can also be incorporated into V-Belt pulleys. No other active pulley design can do this. Imagine, an effective solution to your customer’s impossible to resolve V-Belt breakage issues… that is a simple drop-in fit into their current alternator?
In developing CT Drives we certainly undertook lots of lab testing. In fact, we developed custom test benches that accumulated over a million cycles as they ran 24/7 for months under repeated testing. But we know that bench testing is one thing; real world testing is something else entirely…which is why we’ve outfitted a large cab company, the same one that does OE fleet testing for one of the Big 3, with CT Drives pulleys.
You couldn’t dream up a more brutal testing ground. Constant stop and go traffic and pedal-to-metal gear shifts place extreme stress on drive belts and alternator pulleys. We’ve racked up over one hundred thousand miles under these conditions without a single failure.
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