For wet disk clutches, the energy input is strongly influenced by its friction behavior. However, the friction behavior cannot be simulated and therefore is mostly derived from experimental data for specific clutch systems. This paper presents a new approach for the identification and validation of linear friction models using analysis of variance (ANOVA) and stepwise regression. Therefore, we use experimental data of three different friction systems with paper- and carbon-based friction lining. The designed experiments support an efficient parameter-based analysis of the friction behavior. The obtained models can be used as an input for thermal simulations, for example, but can also support a better understanding of the main influencing factors and are applicable to various friction systems. For validation, the obtained models are applied to measured data. A good correspondence between the simulated and measured friction behavior can be shown for speeds in the investigated operating range. The presented procedure can be easily adapted, for different factors and operation modes, as well as other applications.

Friction behavior is the key parameter for the design of automotive wet disk clutches. On the one hand, the Coefficient of Friction (CoF) level should be high to transmit torque efficiently. On the other hand, the clutch requires a positive slope of the CoF over sliding speed for good controllability, high comfort, and a low tendency to shudder. Clutches used in automatic or dual-clutch transmissions mostly use organic friction lining. These friction systems tend to have low CoF at low sliding speeds due to their high requirements regarding shifting comfort. Nevertheless, they show high values of CoF at high sliding speeds.This study investigates the influence of different steel plate finishes on friction behavior in different application-relevant operation modes such as brake shift, unsteady slip, and micro slip. Each of these operation modes requires an accurate CoF measurement at different sliding speed ranges. Therefore, we use different test rig setups. We characterize the steel plates by their areal surface topography measured with an optical system using focus variation. We discuss differences in the friction behavior of the corresponding tribological systems at different operating conditions.Results show an influence of the steel plate surface finish on the CoF level. Therefore, the surface finish of the steel plate influences the functional behavior of wet disk clutches and engineers should consider the surface finish in the early design phase. We discuss the correlation between commonly used surface parameters and friction parameters.

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 applications 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 influence 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 investigations are carried out on a component test rig. For this purpose, the time of standstill of the clutch is systematically 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 increase in the maximum friction coefficient occurring at the start of the slip switching operation compared with subsequent slip switching operations was observed, which can be attributed to the downtime after a defined 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 contribution to the transferability of investigations of the friction behavior of component test rigs to real applications in which the friction system is exposed to relevant times of standstill and expand the existing knowledge base on test methods.