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#1
09-09-2004, 04:29 PM
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braking analysis
hi,
i have a task of critically analysing the braking system of a prt(private rapid transit ) vehicle. i was wondering what are the most influencing parameters effecting braking performance, and how can i optimise it for the varying wheel base length, c.g height, weight of the vehicle and varying coeficient of friction.. i will be grateful for the help.. 
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#2
09-09-2004, 07:56 PM
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Re: braking analysis
One could write a doctoral thesis on this.
I would suggest: -tire compound (stickiness), pressure, contact patch shape and tread design, (dry pavement-tread squirm, and wet pavement, water shedding. ) -Vehicle weight, and weight transfer; as the vehicle begins decelleration, a greater proportion of the mass shifts to the front wheels. The brake balance, that is, the ratio of braking force, front wheels vs rear wheels must change to compensate, to prevent wheel lock up. -Ability for the brakes to radiate absorbed energy (heat) rapidly, to prevent brake fade over several brake applications. -Ability for the brakes to actually achieve threshold braking, that is, enough force to almost, but not quite lock up the wheel during hard braking.
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#3
09-09-2004, 10:33 PM
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Just for clarification about load transfer (aka weight transfer) no “mass” shifts during braking (with the exception of perhaps fluids, but that can probably be neglected for most calculations). Load transfer occurs because the braking force acts through the contact patch of the tire. Since this force does not act through the CG of the vehicle a moment is generated about the CG.
The result of braking is an increase in load on the front tires, and decrease in load on the rear tires. This allows the front tires to generate a larger braking force than with no load transfer, while the rears tires generate less braking force than with no load transfer. Because the coefficient of friction changes with load at a non-linear rate, the result is a decrease in total braking force with respect to no load transfer conditions. In an effort to reduce the load transfer under braking one could either lower the CG or increase the length of the vehicle.
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