The Mechanical Engineering Department at the University of the Witwatersrand is conducting research on the effect of heat from truck brakes on the temperature of surrounding vehicle components, assisted by donations from BPW, Siemens, CT Hydraulics, Fluid Power Group and Hytrain.
“The operating temperature of these components can have a significant effect on their durability,” says Senior Lecturer, Frank Kienhöfer. “Truck tyre durability is of particular interest as tyre blow-outs can cause severe accidents – we have all seen tyre debris littering our roads.”
Rolling road testing rig
To test the temperatures of the vehicle components surrounding the brakes, the researchers designed and manufactured a customised rolling road test rig. “Testing in the laboratory is safer, cheaper and more repeatable than track testing on a vehicle,” Kienhöfer continues.
Donations from BPW and Siemens
The rig uses ECO Plus 2 axles donated by BPW South Africa. The twin drive rollers are powered by a 30 kW motor controlled by a frequency inverter donated by Siemens.
Keeping the axle load constant
The initial rig design used an hydraulic jack to impose a wheel load to stop the wheels from slipping on the rollers during braking. However, subsequent load cell measurements showed that the vertical load reduced slightly during testing. An hydraulic actuator was proposed to keep the vertical load constant.
Walter Zimmerman from Hytrain provided the expertise to choose the correct actuator. He suggested using a proportional control valve and helped with the sizing of the hydraulic power pack. “We were overwhelmed when Walter convinced CT Hydraulics (Nqoba) to donate the hydraulic cylinder and Fluid Power Group to donate the power pack,” Kienh*#246;fer adds.
Pneumatic actuation and control
In addition to the control system to keep the vertical load constant, another control loop is used to ensure that constant braking power is applied. A Festo proportional pressure regulator adjusts the pneumatic brake pressure applied to ensure consistent braking power is applied.
Temperature measurement
The temperatures at the brake shoe, axle beam and axle bolt are measured using thermocouples. A FLIR T640 thermal imaging camera measures the temperature of the tyres. A non-contact temperature measurement technique like thermal imaging provides an elegant solution to the twisting of wires which would occur if thermocouples were used – although care needs to be taken that the calibration and measurement is done correctly.
Results
Initial results from the tests were extremely interesting. The most significant result was that the tyre walls on the single aluminium wheels ran up to up to 20°C hotter than the tyres on the dual steel wheels. This has lent credence to the theory that truck tyres are more likely to burst on aluminium wheels if the brakes are binding. Correct brake adjustment and maintenance on truck trailers with aluminium wheels is important.
Initial results presented
The initial test results were recently presented at the international conference, Heavy Vehicle Transportation Technology, held in October 2014 in San Luis, Argentina. The response was extremely positive, with one Australian delegate, Dr Peter Hart commenting that he is glad someone is finally looking into this issue. Further tests are being planned, combined with the development of a better understanding of the physics of the problem of how energy is dissipated during braking, raising the temperature of the surrounding vehicle components. ‘We are very excited about this research and the impact it can have on improving truck safety and reducing tyre blow-outs,” concludes Kienhöfer.
For more information contact Frank Kienhöfer, University of the Witwatersrand, +27 (0)11 717 7320, frank.kienhofer@wits.ac.za, www.wits.ac.za
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