The function of an automotive friction brake is to generate a braking torque to retard the road wheel and thus the vehicle to which it is fitted.

Consistent brake friction torque generation under all conditions of use, hot and cold, dry and wet, is a major design objective.

Analysis of Brake Systems

There are two main types of friction brake that have been in common use on road vehicles for many years: the disc brake works by pressing ‘pads’ of friction material against each side of a rotating disc, while in a drum brake the brake linings mounted on ‘shoes’ are expanded outwards against the inner surface of a rotating brake drum. The kinetic energy of the vehicle’s motion is converted into heat by the process of friction, and a key part of the brake design process is that this heat must be effectively and efficiently dissipated by the brake components to avoid problems of overheating.

The function of an automotive friction brake is to generate a braking torque to retard the road wheel and thus the vehicle to which it is fitted.

Consistent brake friction torque generation under all conditions of use, hot and cold, dry and wet, is a major design objective.

Analysis of Brake Systems

Pad length

w– wheel: 2 contact surfaces axle: 2 wheels4 contact surfaces Threshold pressure: ** The pressure of the actuating fluid necessary for effecting the beginning of braking torque in the brake

(For geometric mean radius)

w– wheel: 2 contact surfaces axle: 2 wheels4 contact surfaces Threshold pressure: ** The pressure of the actuating fluid necessary for effecting the beginning of braking torque in the brake

For constant pressure without wear

For uniform wear

Calculate: 1. The wheel brake torque 2. The axle braking torque

50 mm

70 mm

65 mm

parameters values

pressure 1 MPa

Mu (CoF) 0.2 & 0.5

reff 65 mm

Pad area 70mm x 50 mm

methods CoF = 0.2 CoF = 0.5

Theoretical T = 91 Nm T = 228 Nm

FEA T = 94 Nm T = 233 Nm

Contact force

When analysing the mechanics of a drum brake, it is good practice to analyse each brake shoe individually and then combine the two to give the total brake torque.

Considering lining length, the shoe factor is given by

Duo servo with floating link (1st shoe)

Duo servo with floating link (2nd shoe)

Duo servo with floating link (2nd shoe)

Duo servo with guided link

Exercise Q1. Define brake factor and shoe factor. Q2. Using a similar geometry of simplex drum brake in slide no.6, derive the shoe factor, brake factor and brake torque for duplex and duo-servo drum brakes. Q3. Given d = 100mm, m = 55mm, c = 20mm, Re = 90mm, piston diameter = 10mm, efficiency of hydraulic actuation = 0.95, threshold pressure = 0.1 MPa, actuation hydraulic pressure = 2.0 MPa. Calculate and plot brake factor and brake torque versus friction coefficient ( CoF = 0.0 to 0.8) for simplex, duplex and duo-servo drum brakes. Give your comment on the results. Q4. Given the outer and the inner diameter of a disc, Do = 300mm and 240mm, respectively, piston diameter = 50mm, efficiency of hydraulic actuation = 0.95, threshold pressure = 0.1 MPa, actuation hydraulic pressure = 2.0 MPa. Calculate and plot brake factor and brake torque versus friction coefficient ( CoF = 0.0 to 0.8) for disc brakes.