Browse Publications Technical Papers 2010-01-1694

Study of the Relationship between DTV, BTV and BPV over Judder-Type Vibration of Disc Brake Systems 2010-01-1694

Vehicle brake judder is a vibration phenomenon responsible for an expressive number of customer complaints. In order to prevent judder from occurring, new vehicle developments are putting in practice dynamometer and vehicle brake tests to assess the DTV growth and the effectiveness of applied countermeasures, when necessary.
The measurement of DTV is very sensitive and requires high precision sensors. Due to these facts, incorrect DTV measurements are not uncommon, since the rig or vehicle setup, the assembly/disassembly of the sensors or brakes and even the vibration of the dynamometer itself may figure as sources for measurement errors. In the other hand, if the test vehicle or dynamometer is equipped to acquire brake torque and brake pressure variations (BTV and BPV, respectively), those measurements may suffer less interference from external parameters and present good relationship with DTV and judder.
As a study to verify this correlation, discs in different levels of DTV were prepared and assembled on a vehicle, instrumented to vibration measurements. A test procedure with snubs at different pressures was carried out with each disc, as a way to evaluate the condition for critical judder. After that, the same procedure was simulated in an inertia dynamometer, were the BTV and BPV were measured against the different levels of DTV.
As a result it was observed that the BTVrelative measurement, as well as the BPVmaximum measurement, in snubs with pressure between 30 and 50 bar, present well-defined levels which allow identifying if a brake disc DTV is above the acceptable limit for non-generation of vibrations classified as uncomfortable. From this observation, the conclusion is that brake test procedures can incorporate additional snubs with pressure in the range of 30 to 50 bar, in strategically defined stages, where the BTVrelative and/or BPVmaximum measurements may figure as part of the criteria for brake approval.


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