Effects of Water in All-Wheel-Drive Clutch Oil on All-Wheel-Drive Cornering Noise

The effect of water in all-wheel-drive (AWD) clutch oil and on chatter noise due to negative μ-V gradient and inconsistent static friction coefficient was shown in this present study. First, the relationship between the front and rear axle speed delta and the steering angle of an on-demand AWD vehicle during turning was analyzed. After the comparison of the noise of the warranty-returned AWD clutch oil, the water content difference was observed and proven through statistical hypothesis testing. According to tribological studies, a negative μ-V gradient could cause stick-slip and lead to chatter noise. This hypothesis has been verified via a bench test established according to SAE #2 standard. The clutch pack consisted of multiple paper-based friction plates and carbon steel reaction plates, and different water contents in the oil were tested on the test bench. The result showed that differences in water content in the clutch oil could affect the clutch static friction coefficient, and all tested clutch packs presented a negative μ-V gradient at 0–5 rpm. The effect of extra water added to an SUV AWD coupler oil also supported the observation that a certain amount of water in AWD clutch oil could result in unfavorable noise when an AWD vehicle is turning. This noise could be eliminated by changing oil with low water content several times.