Brakes or Breaks? - Explanation on brakes

Going at a high speed, you encounter a kid or a dog or cattle, anything that is a usual sight on Indian roads and you jam the brake pedal. Thats the instant reaction. You literally stand on the pedal hoping for the car to come to a halt in time to avoid a nasty accident. And when it does, you breathe a sigh of relief and thank the 'almighty'. Never do you thank the brakes, do you? Had it not been for this example of technological marvel, you'd surely have crushed that kid or that dog or whatever. Ever wondered how do the brakes operate? Come, let us learn together.

How exactly does that force from your feet result in slowing of the car? The common misconception hass it that the brakes grip against a drum or a disc and the pressure applied is what slows the car. This is just a part of the elaborate explanation. When the brake pedal is pressed, the force from the feet is transmitted to the brakes through a fluid. The force required on the brakes is much higher than the force exerted by the feet, hence the car multiplies that force.

Friction plays an important role in the braking mechanism since the force conveyed to the tyres employs friction as does the transmission of force from the tyres to the road.

Consider the distance of the pedal from the pivot to be five times that of the distance of pedal cylinder to the pivot. Hence the force applied on the cylinder will be five times the force that is applied on the brake pedal. Now, consider the diameter of the brake cylinder to be three times that of the pedal cylinder, so that further multiplies the force by a factor of nine. In total, such an arrangement increases the total force on the brake pedal by a factor of 45.

There are two types of widely used brakes - disc type and drum type. The disc brakes consist of brake pads, caliper and a rotor that sits on the hub. In the actuation of the disc brake, the brake pads squeeze the rotor which transmits the force hydraulically through a channel.

A moving car has some amount of kinetic energy and it increases with the square of velocity. So, if the speed of a vehicle doubles, the kinetic energy increases four times in magnitude. The kinetic energy of a moving car is converted into thermal energy by the friction between the pads and the disc. Most cars are equipped with ventilated discs in order to facilitate better cooling by dispersing air through the discs. The cooling of the brakes dissipates the hear and the car slows down. Such a phenomena follows the law of conservation of energy which states that energy can neither be created nor destroyed, it can only be converted from one form to the other. So, here the kinetic energy is getting converted into heat/thermal energy.

Drum brakes are more complicated and appear complex when opened up. When the drum brakes are applied, the piston pushes the brake shoes against the drum. The brake shoe interacts with the drum and there is a locking action which has a gripping effect between the shoe and the the drum. The drum brakes employ smaller piston than the disc brakes because the extra force provided by the locking action. When the brake is released, the shoes must pull away from the drum. This requires the use of springs. Another set of springs hold the brake shoes in place while helping the adjuster arm return to its original position.

For effective functioning, the arrangement of the brake shoes is such that the shoes must be close to the drum but should not physically touch it. If the distance between the shoes and the drum increases, then the piston will ask for more fluid to travel that distance. This will result in the brake pedal sinking deeper towards the floor on its application. To prevent this, adjusters are made use of. The adjuster has threads on it. When the gap between the brake shoes and drum increases, the adjuster advances the gear by one tooth, hence filling up the gap. This always keeps the shoes in close contact with the drum.

Two semi-circular brake shoes are housed inside a spinning drum. On the application of brakes, shoes expand outwards making contact with the inside of the drum. The friction created due to this contact in-turn creates heat which transfers kinetic energy which helps in slowing you down. The brake shoe pivots at one end and the entire brake pad does not grip against the brake drum. The leading edge is that part of the brake pad which first comes in contact with the drum and is the pad closest to the actuator.

Several technological advancements have been achieved in the braking department. Brakes now come equipped with additional abbreviations like ABS, EBD etc. All this help in enhancing the safety of the system and the car and in turn it enhances the safety of yours. Brakes have always been an essential and necessary equipment and will always remain so. Give them respect, deep respect.