Friction Characteristics of Controlled-Slip Differential Lubricants 660778
Controlled-slip differentials (CSD) improve car operation under wheel slipping conditions. The performance of CSD's is dependent upon two criteria associated with clutch friction: “chatter” and “effectiveness.” “Chatter” is an undesirable noise which may occur during differential action. “Effectiveness” is a measure of the ability of the CSD clutches to transfer torque, during wheel slippage, to the wheel with the greater traction. The objective of this investigation was to definitely establish the cause of chatter, measure CSD effectiveness, and relate friction characteristics of lubricants to CSD operation.
In tests with an instrumented car, it was found that both chatter and effectiveness are strongly influenced by the lubricant. Chatter occurred with lubricants that produced an increase in clutch friction with decreasing sliding speed. Chatter did not occur with lubricants containing friction modifiers which produced a decrease in clutch friction with decreasing sliding speed. Unfortunately, these friction modifiers also reduced the CSD effectiveness by reducing the clutch friction.
To simulate CSD clutch plate sliding under more closely controlled laboratory conditions, the R-H Friction Apparatus was built. Results with this apparatus were correlated with those obtained with the car. Also, deterioration of CSD lubricant friction characteristics in car service was confirmed with the R-H Friction Apparatus.