Judder may fall under the headings of cold or hot judder but by far the most
complex to understand is hot judder. This may result from rotor deformation or an effect
referred to as "hot spotting". It is clear that to minimise the occurrence of thermal judder it is
necessary to avoid excessive heating of the rotor and at the same time avoid significant
variation in temperature across the rotor. To this end the designer must ensure uniform heat
dissipation from the rotor.
In high performance braking applications vented discs are normally used as these provide a
greater cooling surface. These discs increase cooling efficiency by employing braking
surfaces (blades) separated by a number of "ribs" or "vanes" which allow air to pass between
the two blades. To increase cooling efficiency some vented discs use pins to separate the
braking surfaces as this arrangement increases the available area to dissipate the heat. The
cooling efficiency of the brake discs depends on two parameters; the mass flow rate of air
through the disc and the effective heat transfer coefficient on the surface of the disc blades
and vent vanes/pins. "Pin" type vented discs have been found to be good at increasing heat
transfer coefficient but mass flow rates through such discs are generally smaller when
compared to vane type discs.
This paper attempts to define a plausible way of controlling the shape of the columns within a
pin vented disc with a view to finding an optimised configuration for a disc consisting of three
rows of 36 "pins" positioned so that their centre lines are separated by ten degrees, with the
central row of pins offset by five degrees to the outer and inner rows. The optimisation of this
"pin" arrangement attempts to increase the average heat transfer coefficient and the wetted
area in order to enhance the aero-thermal characteristics of the disc to increase heat
dissipation from the rotor in a uniform manner and hence decrease the discs tendency to
judder.
The results presented within clearly show the advantages of increasing the pumping efficiency
of the brake rotor; this is demonstrated by the "high mass flow rate" design. It has also been
shown that increasing the width of the second an third rows of pins produces a decrease in the
flow rate through the disc whereas the first row has an optimal width that creates a venturi at
the inlet which aids inlet velocities. A reasonable correlation has been demonstrated between
the results from the computational fluid dynamic analysis and those gained from empirical
formulas as well as previous computational studies.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)
