GMN >> Freewheel Clutches > Basics > Technology > Speed limit

Speed limit

When torque is transmitted the sprags are in a fixed position between inner race and outer race. Under these conditons - theoretically - there is no speed limit. In backstopping and overrunning applications the influence of centrifugal forces has to be considered.

Series 400

Our sprags could lift off the inner race due to centrifugal forces at a critical speed. In indexing applications the function of the clutch cannot be guaranteed above this critical speed. Please note: The proper function of the clutch is depending on the speed of the sprags themselves, not the speed of shaft or housing which might be different.

The initial speed of the sprags could not be calculated easily, but: The insert element will not run with the turning part (i.e. shaft) and it will also not stand still with the stationary part. The insert elements - and with them the sprags - are stabilizing their own speed anywhere between. The speed limits shown in the tables and data sheets refer to the speed of the insert elements, they do not refer to the speed of shaft or housing!

Series 8000

The sprag design of our series-8000-sprags is a "press-on design": With higher speed the sprags are pressed on the raceways. Due to centrifugal forces they do not lift off. The reason for this effect is the special position of the centre of gravity.

Tests showed that with oil lubrication series 8000 sprags surf on a hydrodynamic lubricating film under constant conditions (v = const.) with rotating shaft. The clutch itself turns very slowly under these conditions and so centrifugal forces do not become effective. The same situation could be expected with grease lubrication at a little bit higher speed level.

 

The rotating speed of the clutch itself depends on size, viscosity and temperature. With a hydrodynamic lubricating film only minimal wear is to be expected.

Please note that in indexing applications due to alternating conditions a hydrodynamic lubricating film cannot be created. Please contact our technical staff for some advice in these kinds of applications.