1986-09-01

Further Experimental Studies in Wet-Brake Friction 861199

This paper describes further experimental efforts to determine friction characteristics that define the chatter potential in wet-brake systems as used in tractors and other off-road applications.
Changes and improvements to a bench facility described at the 1985 Off-Highway Conference are described. Of particular interest is the decision to examine the very low sliding velocity regime, particularly below 0.34 m/s sliding velocity.
Interesting and informative data have been obtained by feeding the input of an accelerometer attached in effect to the caliper brake pads to a frequency analyzer. A spectrum of the energy developed by the vibrating pads over the frequency range of 0 to 250 Hz while the sliding velocity is increased from 0 to 0.85 m/s is obtained. Specifically, the area under the composite frequency curve from 70 to 125 Hz shows good correlation to the chatter propensity of the oil.
The results of tests on several oils will be described. The ultimate purpose of the research is to provide a relatively rapid screening test for evaluating brake oils for the John Deere-type qualification tests.
The overall results emphasize the importance of a low ratio between the breakaway friction and the friction at moderate sliding velocities for low or no chatter.

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