AUTOMOTIVE BRAKING SYSTEM

FUNCTIONS OF THE BRAKING SYSTEM :

9 To stop the moving vehicle in a shortest possible distance/time

9 To help in controlling the speed of the vehicle during cornering etc.

9 To hold the vehicle in stationary position ,after it has been brought to stop

CLASSIFICATION OF BRAKING SYSTEM :

Based on purpose - Service brake and Parking brake

Based on construction Drum brake and Disc brake

Based on method of actuation Mechanical , Hydraulic , Vacuum , Air

Based on location Wheel , Transmission and exhaust

Based on energy supplied Manual , servo/power assisted , power

REQUIREMENTS OF THE BRAKING SYSTEM :

The brakes should stop the vehicle within a reasonable distance.

The retardation should be smooth and free from jerk.

The braking system should not be affected by water , heat , dust etc.

Pedal effort required by the driver must be optimum so as not to strain the driver.

The wear and tear of the material of the brake lining should be minimum for longer life

The brake system capable of dissipating heat generated very quickly.

BRAKE FORCE REQUIRED TO STOP THE VEHICLE :

A vehicle with a 100 hp engine require about 60 sec to accelerate the vehiclefrom 0 to 100 kmph . If the same vehicle is required to be stopped from 100kmphto 0 kmph in not more than 6sec then brakes must do the same amount of workas engine did but in one tenth of the time . This means brakes must develop 1000 hp to stop the vehicle .

If the weight of the vehicle is doubled then brake power must be doubled.

if the speed of the vehicle is doubled then stopping power must be four times.

if both weight and speed is doubled then brake power must be increased 8 times

CAPACITY OF A BRAKE :

9 Unit pressure between the braking surfaces.

9 Coefficient of friction between the braking surfaces.

9 Projected area of the braking surfaces.

9 Peripheral velocity of the brake drum.

9 Ability of the brake to dissipate heat equivalent to the energy being absorbed

Brake classification Based on Purpose

Service Brake and Parking Brake

Brake classification Based on construction

Drum brakes have a servo action that results from the 'wrapping'effect of (usually) the leading shoe. That explains why the leading shoe generally has more lining than the trailing shoe. As the leading shoe engages on the surface of the drum, its geometry causes it to set tighter and transmit some force to thetrailing shoe. Cars with drum brakes generally have noticeably less braking performance when stopping in reverse

A valve that is actuated when the brake pedal is depressed reduces atmospheric pressure on the master cylinder side of the servo diaphragm. The higher atmospheric pressure on the other side assists the brake actuator push rod to apply force to the piston in the master cylinder. This is the most common arrangement in modern vehicles. In gasoline-powered vehicles the engine manifold vacuum is used to provide the pressure differential.

The brake system found in diesel-powered vehicles typically uses a vacuum pump to provide the vacuum since manifold pressure in a diesel is the same as atmospheric.

Trucks with air brakes use compressed air to push air servos (commonly called 'pancakes') located at each wheel. When air pressure is removed, a spring pulls the brake tight. A truck with air brakes will not roll until it builds up air pressure.

Drum brakes have a servo action that results from the 'wrapping' effect of (usually) the leading shoe. That explains why the leading shoe generally has more lining than the trailing shoe. As the leading shoe engages on the surface of the drum, its geometry causes it to set tighter and transmit some force to the trailing shoe. Cars with drum brakes generally have noticeably less braking performance when stopping in reverse.

Band brakes, similarly, benefit from the wrapping servo effect and also work poorly in reverse but you typically don't find band brakes on anything larger than a riding lawnmower

Servo brake

Brake Rotor

Sliding CaliperAs you apply brake pressure, the hydraulic fluid pushes in two directions. It forces the piston against the inner pad, which in turn pushes against the rotor. It also pushes the caliper in the opposite direction against the outer pad, pressing it against the other side of the rotor.

Fixed Caliper : There is a piston on each side of the caliper

(a) by using a servo mechanism which adds to the drivers effort although that effort remains a considerable part of the total effort applied to the brakes.

(b) using power operation in which case the effort of the driver is a controlling effort only and is not transmitted to the brakes at all.

The source of the additional effort supplied by a servo system may be

(a) the momentum of the vehicle itself,

(b) vacuum in a reservoir, obtained by connecting the reservoir through a non-return valve either to the induction manifold of the engine or to a separately driven exhauster,

(c) oil under pressure supplied by a pump driven by the engine or some part of thetransmission system,

(d) air under pressure supplied by an air compressor driven by the engine.

Brake Hose

Cable operated Solid bar connection Single-circuit hydraulic Double-circuit hydraulic Brake by wire

Brake Actuators

Cable operated

Solid bar connection

Single Circuit Actuator

Dual circuit Actuator

Brake by wire

Brake-by-wire represents the replacement of traditional components such as the pumps, hoses, fluids, belts and brake booster with electronic sensors and actuators.

Brake-by-wire technology is still under development and has not been widely commercialized mainly due to the safety-critical nature of brake products.

brake-by-wire systems that have been developed fall into one of two categories: electro-hydraulic and electro-mechanical.

Mercedes-Benz and Toyota already use almost fully brake-by-wire systems.

Brake By Wire actuator

electro-hydraulic

Electro mechanicl circuit

Brake valve