If the internal clutch mechanism is bad, the pulley may slip and fail to drive the alternator, or it may remain locked all the time — increasing noise, vibration and stress on the belt drive system. This type of pulley also has a one-way overrunning clutch inside the hub as well as an internal torsion spring to further dampen vibrations in the belt drive system. The spring acts like a shock absorber to cushion the hub. This reduces noise at idle and low engine speeds, and helps dampen harmonic vibrations at higher speeds.
If the clutch or spring inside the pulley has failed, the pulley may fail to drive the alternator, or it may create vibrations and noise. How can you identify these types of alternator pulleys? Solid pulleys typically slide onto the alternator shaft or are press-fit and held in place with a large bolt on the end of the shaft. Advertisement Some replacement alternators come with new pulleys already installed and some do not.
If an alternator with an OAP or OAD pulley is being replaced, and the replacement unit does not have a pulley installed, or it is a simple pulley and not the same type of OAP or OAD pulley, the original pulley can be removed from the old alternator and installed on the new unit — provided it is in good condition. However, on high-mileage vehicles, replacing the original OAP or OAD pulley with a new one is recommended to ensure trouble-free operation.
What happens if a replacement alternator does not have the same type of pulley as the original? The result will likely be noticeably higher NVH while driving.
The resulting vibrations are transmitted to the power-train drive elements. Naturally, this has an adverse effect on the noise development and the service life of the drive belt. With its overrunning clutch, the overrunning alternator pulley cancels out these vibrations and also enables the engine rpm to be quickly reduced in the event of sudden load changes. Alternator decoupler pulleys, as a special variant of the overrunning alternator pulley, also perform a damping function.
An overrunning alternator pulley essentially consists of the following components:. Due to the coupling function of the overrunning alternator pulley, the torque is only transmitted in one direction.
When the overrunning belt pulley is replaced, the V-ribbed belt and the tensioning pulleys and deflection rollers should also be replaced at the same time. People think alternators are easy to spin, this may be true when they are sitting on the counter at the auto parts store but in real life when alternators are mounted on the vehicle and turned on charging, they are very hard to turn, so they do not "free wheel" while charging on the vehicle.
As soon as you slow down your motor the alternator is under such charge load that the alternator itself will slow down the motor.
I reciently spoke with a customer that purchased a solid pulley conversion to replace his failed clutch pulley. He was quite upset in that the alternator works just fine but the clutch pulley failed and he couldn't find a clutch pulley for his alternator.
Solid pulleys do not have a clutch that can fail. They won't leave you stranded from a failed clutch. All rights reserved. Trade marks and trade names used for reference purpose only. Use of the OAP also enables more cost effective design of other components in the overall belt drive system. Volker Ploetz, senior manager of transmission components at Schaeffler Automotive, says: "The overrunning alternator pulley works in a similar way to the freewheeling of a bicycle pedal, whereby only the acceleration proportion of the crankshafts rotational irregularities is used to drive the alternator.
The advantages from this include more effective damping of belt oscillations, which means you no longer need idler pulleys or damping pulleys. You also get a reduction of tensioning forces and lengths, as well as improved noise behaviour, reduced belt width and increased system life.
The use of alternators with high inertia is also possible. In terms of assembly, the overrunning alternator pulley is easy to fit as no separate fasteners are required. The component was regarded early on as key for eliminating the rotational irregularities from the belt drive of the new generation of high torque, direct-injection diesel engines.
It is also now included in an extensive list of measures for optimising the fuel consumption of internal combustion engines. The Schaeffler Group currently manufactures more than different types of belt pulley with OAP and it hopes that its positive effect to engine design gets fair consideration by engineers in the future.
Structural design The overrunning alternator pulley consists of a pulley with an outside diameter suitable for using a poly-V belt, a one-way clutch unit with bearing supports, an inner ring and two seals. Following installation, an end cover is snapped onto the front of the alternator shaft to protect it from ambient media such as penetration of contamination like salt water deposits. A modular system has been developed for overrunning alternator pulleys to provide an economical and flexible solution for customer enquiries.
The one-way clutch unit and the seal components are standard parts.
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