Nothing Impacts Starter Reliability Like the Clutch

More Contact Points Deliver Better Engagement Reliability

TDI’s proprietary sprag clutch design is the industry’s most reliable because of its ability to handle high torque and its operational characteristics which provide the longest service life intervals of any air starter.   What we’ve done is pack 22 contact points which evenly disperses the torque through the clutch vs. the 3 or 13 points common on other style clutches.  The result is more load carrying members, greater contact area and the ability to handle torque loads that could cause other clutches to fail.  In addition, when the TDI clutch is disengaged (during engine operation) the sprags will actually lift off the inner race thus eliminating any contact and therefore virtually eliminating wear during the normal engine run hours during operation.  

 SPRAG CLUTCH MODES of OPERATION

Notice the 22 points of contact on the TDI sprag clutch.  The most prevalent clutch system in the industry only has 3 points of contact which is inherently less reliable and often times requires specific ramp rates and controls to prevent overloading the 3 knife edge point on this pawl and ratchet style clutch.   Between the inner and outer races on the TDI Sprag clutch there are a series of cams, or  sprags.  As the starter begins to rotate the inner race rotates and engages the sprags with the outer race, the sprags wedge and connect the outer race so that the entire system turns as one and in the direction to transmit torque and speed to the engine.  There is no wear occurring at this phase as there is no relative motion between the inner and outer race.  The system is simply turning and transmitting torque much like a single shaft.    

As the engine lights and the outer race begins to turn faster than the inner race, the sprags disengage and the starter air supply is turned off and the unit comes to a rest.  The outer race continues to rotate freely with the engine.  As the engine speed increases the sprags will pivot and will ultimately lift completely off the inner race and rotate with the outer race at engine speed.   Therefore, during engine operation the sprags are no longer in contact with the inner race thus eliminating wear during the normal engine operation.    

The result? 

The industry's most reliable clutch system and the industry's most reliable air starters. No other clutch assures trouble free operation like the TDI Sprag clutch.