• The bedding-in process on disc brakes contact pressure distribution and its effects.

      Loizou, Andreas; Qi, Hong Sheng; Day, Andrew J. (24/11/2010)
      Given that most of the working life of a brake pad life is spent in the bedded condition, it is important to examine the conditions of a fully bedded contact interface. An experimental and a numerical method are combined. Contact pressure and its effects (heat generation/partition and temperature rise) for the drag braking process with and without bedding are compared. The real contact area is also measured and found to be increased for the bedded interface. This results to the contact pressure being ¿more¿ evenly distributed than before. Spreading the contact pressure also results in increasing the total heat transfer between the disc and pad since now more heat can be transferred from the pad (where it is generated) to the disc. It is concluded that in order to have a reliable simulation it is recommended that the bedding-in effects are introduced in the simulations.
    • A numerical and experimental study on the factors that influence heat partitioning in disc brakes

      Loizou, Andreas; Qi, Hong Sheng; Day, Andrew J. (Scientific Society of Mechanical Engineering (GTE), 2010-06)
      To investigate the heat partition on a vehicle disc brake, a small scale test rig with one contact interface was used. This allowed the disc/pad contact temperatures to be measured with fast-response foil thermocouples and a rubbing thermocouple. Based on the experimental conditions a 3D symmetric disc brake FE model has been created. Frictional heat generation was modelled using the ABAQUS finite element analysis software. The interface tribo-layer which affects heat partitioning was modelled using an equivalent thermal conductance value obtained from the authors¿ previous work. A 10 second drag braking was simulated and the history and distribution of temperature, heat flux multiplied by the nodal contact area, heat flux leaving the surface and contact pressure was recorded. Test rig and FE model temperatures were compared to evaluate the two methods. Results show that heat partitioning varies in space and time, and at the same time contact interface temperatures do not match. It is affected by the instantaneous contact pressure distribution, which tends to be higher on the pad leading edge at the inner radius side. They are also affected by the thermal contact resistance at the components contact interface.
    • A study of commercial vehicle brake judder transmission using multi-body dynamic analysis

      Hussain, Khalid; Yang, S.H.; Day, Andrew J. (2007)
      Braking-induced forced vibration, known as brake judder in road vehicles, causes dissatisfaction to drivers and passengers and also damage and possible early failure in components and systems. In this paper, the transmission of judder vibration from the point of generation (the brake friction pair) through the vehicle structure to the driver is investigated for the particular case of a heavy commercial vehicle. The investigation uses a computer simulation multi-body dynamic model based on the automatic dynamic analysis of mechanical systems software to identify any characteristics of the vehicle suspension design that might influence the vibration transmission from the wheel to the driver. The model uses a simplified rigid chassis and cab to lump the chassis parameters, so that the investigation can focus on the front axle/suspension design, which is a beam axle leaf spring arrangement, and the rear axle/suspension assembly, which is a tandem axle bogie design. Results from the modelling indicate that brake judder vibration is transmitted to the chassis of the vehicle through a leaf spring `wind-up¿ mode and a `walking¿ mode associated with the rear tandem axle. Of particular interest is the longitudinal vibration transmitted through the chassis, since this creates a direct vibration transmission path to the cab and driver. The simulation results were compared with the previously published experimental work on the same design of commercial vehicle, and agreement between the predicted and the measured vibration characteristics and frequencies was found. It is concluded that the rear suspension design parameters could affect the transmission of brake judder vibration to the cab and driver and that a tandem rear axle offers some design opportunity to control the transmission of brake judder vibrations from the wheel to the cab and driver. Given that brake judder has so far defied all attempts to eliminate completely from vehicle brake systems, this is potentially an important opportunity.