internal expanding shoe brake

INTERNAL EXPANDING SHOE BRAKE

1. Introduction

As the name implies, this type of brake is provided internally on the brake drum. In olden days band brakes were used in automobiles, which were exposed to dirt and water. Their heat dissipation capacity was also poor. These days, band brakes have been replaced by internally expanding shoe brakes having atleast one self-energizing shoe per wheel. This results in increased friction, giving great braking power without excessive use of pedal pressure:

2. Working Principle

Fig.9.15 shows an internal expanding shoe brake. This consists of two shoes S1 and S2; the outer surfaces of which are lined with some friction materials. The shoes S1 and S2 are pivoted about the fulcrums O1 and O2 respectively. The other ends of the shoes are in contact with a cam.

When the cam rotates, the shoes push outwards against the rim of the drum. The friction between the brake linings and drum, produces braking torque, reducing the speed of the drum. The shoes are normally held in off-position by a tension spring. The drum encloses the entire brake mechanism, protecting the brake lining from dust and moisture.

For anticlockwise rotation of the drum, the left hand shoe is known as primary or leading shoe, while the right hand shoe is known as secondary or trailing shoe.