Why Use a Torque Limiter? A jam-up in a machine, conveyor, etc. causes the rotating components of the drive-train to stop suddenly. When this occurs, the inertia of these components will transmit a torque that is several times higher than the normal operating torque. As a result, the weakest component in the drive can be damaged or broken.

Basic Principle: American Autogard Torque Limiters employ the basic ball-dent principle. American Autogard has, through long experience, developed a highly sophisticated design from this basically simple principle. This design, together with the highest quality materials and workmanship, provides reliable, accurate overload protection.

Normal Operation: Torque is transmitted through balls seated in detents in the opposing faces of two plates, one of which is connected to the driving member [motor or gearbox output shaft, etc.] and the other to the driven member [sprocket, sheave, timing pulley, jack-shaft]. The plates are held against the balls by a spring load or air pressure, which can be adjusted to provide required torque.

Overload Condition: Autogard provides a positive drive until the torque reaches the pre-set value. At this point the tendency of the balls is to roll from the detents to overcome the thrust of the spring load or air pressure. The balls then force the plates apart and roll free, providing a smooth, instantaneous and complete disengagement of the drive. The plates are through-hardened alloy steel, insuring low wear, long life and constant torque setting.

All of Autogard Torque Limiters utilize the above principle. The specific construction of each, however, is modified with respect to the manner in which it runs during disengagement and the manner in which it is reset.

A reliable torque limiter should provide:

1. Adjustable over a wide torque range- to permit adjustment for the actual needs of operating and start-up conditions, which may be difficult to calculate.
2. Accurate, consistent disengagement at the set torque- to avoid nuisance tripping, and insure protection, even after numerous disengagements.
3. Quick easy resetting to reduce expensive downtime.
4. Complete disengagement to protect the drive train and driven equipment from damaging inertia.

Autogard Torque Limiters provide all the above features, whereas other mechanisms fall short in one or more of these important requirements.

Every Autogard is easily adjustable through a wide torque range permitting field adjustment to the precise requirements of the application. Shear pins, on the other hand, are inconsistent in their shearing or breaking point and can only be "adjusted" for a change of torque by using pins of a different size or material. Other devices may permit adjustment, but only at specific settings of large increments.

Autogard can be set very accurately and will be repeatable from disengagement to disengagement because it operates in a freely rolling condition. By comparison, the slipping torque of a friction device varies due to environmental conditions such as moisture, dust & heat. Furthermore, due to continual wear when slipping, these devices require frequent adjustment to prevent nuisance slipping. Some other ball-type and cam-type devices operate with sliding friction. This causes substantially greater variability than the rolling action of Autogard. Shear pins fatigue, then shear at lower than desired torque, requiring frequent replacement. Some are replaced with pins providing a much higher shearing point, resulting in no protection at all.

The resetting of an Autogard is quick and easy and can be achieved manually or automatically, depending upon the type of unit selected. After resetting, it is again ready to disengage at the original torque setting. Other torque limiting devices, such as shear pins, cam devices, etc. can be difficult and time consuming to replace or reset.

When an overload occurs, the disengagement of an Autogard is complete and instantaneous. This disconnects the potentially damaging kinetic energy from the components in the drive train and in the driven equipment, thus providing total protection. While and electrical overload switch will protect the motor from damage, it does not act instantaneously when an excess torque is reached, nor does it disengage the inertia of the motor from any of the connected equipment. Friction devices do not disconnect and will continue to transmit torque when a machine is jammed.