Types and functions

For a more detailed explanation see http://www.drive-lines.com/index_clutches.html.

Different applications require different types of torque protection. When working properly, these devices can make a huge difference in production and efficiency. When worn or otherwise not working, they are akin to achors chained to your ankle.

As with PTO shafts in general, torque devices are generally misunderstood, under maintained, and abused. Some of these devices, such as radial pin clutches and overrunning devices, require minimum maintenance. Others, such as friction clutches, need a constant watch.

For the purposes of this article we will address the three most popular units.

FRICTION CLUTCHES:

All friction clutches depend on a series of layered discs bound together with a spring(s) that use the principal of friction to control the amount of torque transmitted. Although manufacturers stand by their laboratory established torque settings, we in the real world understand that the torque rating of any friction device is a fluctuating variable dependent upon many factors.

The biggest factor is how many times the clutch has "broken" (spun or slip). At some point the friction linings (discs) begin to loose material thus affecting the setting of the clutch. If the discs are not changed or the clutch is an adjustable one and is not tightened, eventually the unit will spin continuously.

On the other hand, if the clutch is over tightened or the discs have welded themselves together via electrolysis, it will never break and thus will not protect the equipment it was intended to.

There is nothing worse than a frozen clutch.

Each season at the very least friction clutches should be disassembled, cleaned, and reassembled. Any parts worn beyond a slight etching should be replaced. Discolored parts have been over heated and should also be replaced. Judging the condition of component parts requires experience and at that is a tricky business.

Concerning friction clutches we have a saying, "It's an art, not a science."

In spite of the difficulties and uncertainties, friction clutches do a wonderful job for what they are intended to do. (equipment protection)

Shear Bolt Yokes

Shear bolt yokes consist of two basic parts which share multiple ball bearings and may be turned independently of each other. A bolt then secures the parts to act as a shear. At a given torque, this bolt will break and must be replaced before proceeding with torque transmission. The given setting of a shear bolt may vary with the type of bolt used. (hardness) However, factory settings using factory bolts are very dependable.

More and more implements are utilizing the shear bolt as a means of protection. They are relatively cheap and serve as a last resort to avoid expensive equipment repairs. Almost no maintanence required. Grease after replacing bolt or once a season.

"Automatic" devices are available to do the same chore and will reset themselves when the RPM is brought to zero.

Overrunning Devices

Overrunning devices will deliver torque in one direction only. They are intended to protect tractors and powertrains from inertial loads and what we call "backlash". Whether there is a fan or a flywheel or simply the momentum of the equipment that may present danger to other components, these units will save the day.

In our opinion every tractor should have this feature built into its PTO BOX. Many implements would benefit by, and run more efficiently by incorporating overrunning protection. The life expectancy of the equipment may also improve using this type of protection.

Grease regularly.

This is one of the few technical innovations that is undersold.