Fundamentals of Anti-Shudder Durability: Part II - Fluid Effects

Friction plate degradation and/or friction plate glazing has often been related to the loss of friction control in automatic transmissions. However, in JASO SAE No.2 and LVFA tests, friction material glazing has been found to not be a sufficient condition for the loss of anti-shudder performance or a reduction in torque capacity durability. Therefore, changes in automatic transmission fluid properties rather than changes to the friction surfaces would be expected to play a dominant role in controlling anti-shudder performance and torque capacity. Earlier theoretical studies have proposed that friction in wet clutches is a combination of boundary and hydrodynamic friction. Therefore, changes in these properties should control anti-shudder durability and torque capacity. In this paper, we confirm that boundary and thin-film friction contribute to friction measured in JASO SAE No.2 and LVFA tests. In addition, we show that changes in these critical physical properties of fluids are related to anti-shudder and torque capacity durability.