Influence of the Time of Standstill on the Breakaway Torque of Wet Disk Clutches

Detailed knowledge of the influences on the frictional behavior is crucial for reliable operation of safety-relevant, wet-running multi-plate clutches. The breakaway torque is of particular interest for safety-critical appli- cations such as safety brakes and clutches. While influences of the tribological system by variation of friction partners, lubricant and operating conditions are usually the focus of current investigations, the influen¬ce of the time of standstill between a preceding tribological load and a subsequent breakaway of the wet disk clutch is not considered. To determine this influence, experimental investigati¬ons are carried out on a component test rig. For this purpose, the time of standstill of the clutch is systema¬tically varied after preceding load shifts and the clutch is then broken away. During these investigations, it is shown that the downtime of multi-plate clutches with sinter friction lining has considerable influence on the frictional behavior in the first switching operations after actuation. An influence can already be clearly seen at a standstill time of approximately 15 minutes. An in¬crease in the maximum friction coefficient occurring at the start of the slip switching operation compared with subsequent slip switching operations was observ¬ed, which can be attributed to the downtime after a de- fined preload. Influences of the disk temperature are considered by measuring the outer disk temperature. The influence is attributed to the change of the boundary layer during the standstill. The results provide a con¬tribution to the transferability of investigations of the friction behavior of component test rigs to real appli¬cations in which the friction system is exposed to rele¬vant times of standstill and expand the existing know¬ledge base on test methods. © 2022 Expert Verlag. All rights reserved.