Trucks for refrigerated food transport or air-conditioned buses require more and more electrical power, which in turn means that larger and larger alternators must be driven by the trucks Diesel engine.
Unfortunately, as the alternator increases in size, its inertia increases exponentially. This results in conflict between the high inertia generator trying to run smoothly at a fixed speed and the fidgety Diesel engine delivering nothing but torque peaks.
The victim of this incompatibility is usually the drive belt between the alternator and the Diesel crankshaft pulley. It stretches, swings and vibrates until drive to the alternator fails either by the belt jumping off both pulleys, or with the belt being shredded as it passes over the pulley flanges.
In any event, without alternator drive the bus or truck must soon stop until the drive is repaired.
‘Mr Angry’ soon appears either as one of the passengers stuck on a bus which is rapidly warming, or from the suppliers (or customers) of rapidly melting food on the truck.
STIEBER have designed an alternator pulley with an integrated overrunning clutch which helps to eliminate belt failure.
From the outside, it looks like an ordinary pulley, but inside the boss there is a bearing supported roller-ramp type overrunning clutch. Just like the freewheel on a bicycle the overrunning clutch transmits torque when the driven part tries to run slower than the driver. If the driven part tries to run faster than the driver it is free to do so.
Greased for life, the unit is maintenance free with centrifugal force keeping the lubricant where it is required - between the rollers and the outer race.
Typically, the overrunning clutch pulley is mounted on the alternator shaft and allows the alternator to overrun between the engine firing cycles.
The torque measured on an alternator shaft fitted with a standard pulley looks like an earth quake magnitude 7 on the Richter scale. With the overrunning clutch pulley fitted the torque curve is almost a flat line.
Technically, this is a demanding application. If for example the Diesel runs at 2000 rpm, the clutch must cope with 3 firings per engine rotation, or 6000 per minute.
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