The Unconventional Guide to Automobile Brake Systems

WHAT IS BRAKE?

             A brake is a mechanical device which retards the motion of the moving object or automobile safely within minimum possible time or distance to either stop it or to reduce the speed of it.

WORKING OF BRAKES:

              When we apply brakes then the braking effort from the operator/ the person is transferred to brake shoe or brake pad via mechanical, hydraulic or any type of linkage present in the system, then that made the brake shoe or brake pad squeeze or rub against brake drum or disc. Due to the friction between them the kinetic energy of moving parts is converted into heat and finally the vehicle or moving object gets stopped. 

TYPES OF BRAKES:

Mechanical Brakes 

       Drum Brakes

       Disc Brakes

Hydraulic Brakes

Air Brakes

Power Brakes

Air Over Hydraulic Brakes

Vacuum Brakes

Electric Brakes

       Electrically Actuated Magnetic Brakes 

       Electrically Actuated Friction Brakes

DRUM BRAKES:

              The drum brake has a metal brake drum that encloses the brake assembly at each wheel. Two curved brake shoes expand outward to slow or stop the drum which rotates with the wheel.

WORKING OF DRUM BRAKES:

              Drum brakes work on the same principle as the disc brakes i.e. the friction between the brake shoe and the drum. the shoes press against a rotating surface . In this system, that surface is called a drum. Drum brake also has an adjuster mechanism, an emergency brake mechanism and lots of springs. The shoes are pulled away from the drum by the springs when the brakes are released. 

DISC BRAKES:

               

             In a disc brake, the fluid from the master cylinder is forced into a caliper where it presses against a piston. The piston, in turn, squeezes two brake pads against the disc (rotor), which is attached to the wheel, forcing it to slow down or stop.

            The disc is directly exposed to air hence cooling is also better. It is more reliable and efficient than conventional drum brakes. Some problems may occur like run-out, cracking and scarring or rusting of the disc but technology is changing every day and developing better materials for brake assembly components. Nowadays disc brakes are widely used in front wheel of motor bikes and cars.

HYDRAULIC BRAKES:

               Hydraulics is the use of a liquid under pressure to transfer force or motion or to increase an applied force. The pressure on a liquid is called hydraulic pressure. And the brakes which are operated by means of hydraulic pressure are called hydraulic brakes. These brakes are based on the principle of Pascal’s law.

ADVANTAGES OF HYDRAULIC BRAKES:

1) The equal braking effort to all the four wheels. 

2) Less rate of wear (due to absence of joints compared to mechanical brakes)

3) Force multiplication (or divisions) very easily just by changing the size of one piston and cylinder relative to other.

DISADVANTAGES OF HYDRAULIC BRAKES:

1) Even slight leakage of air into the braking system makes it useless.

2) The brake shoes are liable to get ruined if the brake fluid leaks out. 

POWER BRAKES:

              Power brakes are a system of hydraulics used to slow down or stop most motor vehicles. It uses a combination of mechanical components to multiply the force applied to the brake pedal by the driver into enough force to actuate the brakes and stop a vehicle that can weigh several tons.

              The brake pedal is connected to the vacuum booster which is the first step of the force multiplication. The booster passes the force to the master cylinder which compresses a liquid and forces it through the brake lines to the brakes themselves. 

             The liquid that is pushed into the brakes activates the brake calipers which in the case of disc brakes, push against the brake rotor causing friction that slows and eventually stops the rotation of the vehicle's wheels. In the case of the drum brakes, pistons push two shoes against the brake drum accomplishing the same effect.

AIR BRAKES:

            We see on most of the heavy vehicles like trucks, containers, and trailers, 'AIR BRAKES' is written on them. An air brake or, more formally, a compressed air brake system, is a type of friction brake for vehicles, in which compressed air developing the pressure on the brake piston is used to apply the pressure to the brake pad needed to stop the vehicle. 

             Air brakes are used in large heavy vehicles, particularly those having multiple trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers in addition to their use in road wagons.                      George Westinghouse first developed air brakes for use in railway service. He patented a safer air brake on 5th March 1872. Westinghouse made numerous alterations to improve his air pressured brake invention, which led to various forms of the automatic brake. In the early 20th century, after its advantages were proven in railway use, it was adopted by manufacturers of trucks and heavy road vehicles.

AIR-OVER-HYDRAULIC BRAKES:

              The air-over-hydraulic brake system combines the use of compressed air and hydraulic pressure for brake operation. The air-over-hydraulic brake system has an air-over-hydraulic power cylinder that contains an air cylinder and a hydraulic cylinder in tandem. Each cylinder is fitted with a piston and a common rod. The air piston is of greater diameter than the hydraulic piston. This difference in the two pistons results in much greater hydraulic pressure than air pressure admitted to the air cylinder. Valve action varies with the amount of pressure applied to the brake pedal.

            When heavy brake pedal pressure is applied by the operator for hard braking, the hydraulic pressure in the master cylinder (which operates the valves) causes greater valve movement. As a result, the valve admits more air pressure into the air-over-hydraulic power cylinder and this higher air pressure causes a stronger braking action.

VACUUM BRAKES:

              In a vacuum brake system, depressing the brake pedal opens a valve between the power cylinder, which contains a piston, and the intake manifold to which the power cylinder is connected. When you apply the brakes, air is exhausted from the cylinder head of the piston. At the same time, atmospheric pressure acts on the rear side of the piston to exert a powerful pull on the rod attached to the piston.

            When the brake valve is closed, the chamber ahead of the piston is shut off from the intake manifold and is opened to the atmosphere. The pressure is then the same on both sides of the piston; therefore, no pull is exerted upon the pull rod. The brakes are released and the piston returned to its original position in the power cylinder by the brake shoe return springs.

ELECTRIC BRAKES:

           The electric current controlling the brake through the electromagnet is provided from a brake controller which provides the control current from the towing vehicle. There are different types of brake controllers on the market, each with their own advantages and disadvantages.

          The current controlling the brakes from the towing vehicle is originating in the battery/alternator of the towing vehicle via the brake controller and then transferred via wiring through the electric brake pin in the trailer connector through the trailer wiring to the electromagnet and back through the trailer wiring to the trailer connector and to the towing vehicle chassis/frame through the ground pin in the trailer connector. To minimize interference between vehicle lighting and brakes the circuits shall be as separated as possible.

              Electric brakes are devices that use an electrical current or magnetic actuating force to slow or stop the motion of a rotating component. They are used in industrial and vehicular braking applications that require fast response times and precise tension control.

             There are two main types of electric brakes: magnetic and friction. In addition to type, Some subtypes for electric brakes are specified by operating specifications, engagement mechanism, measurements and shaft configuration, brake materials, and features.

Types of Magnetic Brakes

              Magnetic brakes are non-contact brakes that use magnetic fields to actuate the braking components. There are four types.

1) Permanent Magnet Brakes:

              Permanent magnet brakes stop or hold a load when electrical power is either accidentally lost or intentionally disconnected. They are sometimes called "fail safe" brakes and use a permanent magnet to attract a single face armature. As the brake is engaged, the magnets create magnetic lines of flux, which can turn to attract the armature to the brake housing. 

             To disengage the brake, power is applied to the coil, which sets up an alternate magnetic field that cancels out the magnetic flux of the permanent magnets. Permanent brakes are engaged when no power is applied to them and can hold or stop when power is lost or unavailable.

2) Electromagnetic Brakes:

               Electromagnetic brakes have a coil in a shell, a hub, and an armature. An electrical circuit engages the brake as it energizes the coil. The current runs through the coil and generates a magnetic field. The magnetic flux acts directly between the armature and field. The armature is pulled into contact with the rotor when the magnetic flux overcomes the air gap between the armature and field. 

              All of the torque comes from the magnetic attraction and coefficient of friction between the steel of the armature and the steel of the brake field. Deceleration occurs when the armature contacts the field, and the torque transfers into the field housing and machine frame. Turing off power causes the flux to fall rapidly, the armature to separate, and disengagement to occur. Springs are used to helping push the armature away from the surface and maintain an air gap.

3) Eddy Current Brakes:

              Eddy current brakes develop torque by the direct magnetic linking of the rotor to the stator. A magnetic field induces a voltage in moving objects and the induced voltage causes an eddy current to flow in any conducting objects. The electrical current is sent to coils, which alternate polarities, creating an electromagnetic field. This change in magnetic flux induces a small circulating current in the conductor called an 'eddy current'.

               Eddy currents are generated in two rotors as they spin through the field and slow the rotation of the driveshaft. The first current created generates an opposing current. The counter-opposing flux and Lorentz force reduce the velocity of the object. Ohmic losses and significant heating are also produced by the current. Eddy current brakes must have a slip between the rotor and the stator to generate torque.

There are two types of Eddy current brakes.

i) Rotational Eddy Current Brakes:

              Rotational or circular brakes are connected to a rotating coil and magnetic field between the rotor and the coil, creating a resistance that's used to generate electricity. A braking force is possible when the electric current is passed through the electromagnets.

ii)Linear Eddy Current Brakes:

             Linear eddy current brakes consist of a magnetic yoke with electrical coil positioned along the rail. The coils are magnetized, alternating as south and north magnetic poles.

4) Hysteresis Powered Brakes:

             Hysteresis powered brakes have a wide torque range. They have a reticulated pole structure and a specialty steel rotor/shaft assembly that are fastened together, but not in physical contact. The drag cup can spin freely until the field coil is energized by a current/voltage, creating an internal magnetic flux. The air gap between the pole structure and the rotor becomes a flux field and magnetically restrains the rotor. This provides the braking action between the pole structure and the rotor.

               When electricity is removed from the brake, the rotor is free to turn, and no relative force is transmitted between either part. Torque is only produced through a magnetic air gap that does not use friction or shear forces. Control over torque is done through the DC current to the field coil. The amount of braking torque transmitted by the brake is proportional to the amount of current flowing through the field coil.

Types of Electrically Actuated Friction Brakes:

            Although many electric brakes use mechanical methods for actuation, others rely on friction. There are several types of frictional brake devices.

i) Band Brakes: (Electrically Actuated)

               Band brakes are the simplest electric brake configuration. They are often used as a back-stop mechanism to prevent reverse rotation. These brakes have a flexible band of leather, rope, or steel with a friction lining that is wound around a rotating drum. One end of the band passes through the fulcrum of the actuating lever and frictional torque is then generated when tension is applied to the band. The band will lock up the brake for rotation in one direction and when friction is placed on the band, it loosens for rotation in the opposite direction.

               Band brakes are often used in lifting applications to prevent the object being hoisted from falling when the user stops pulling.

ii) Drum Brakes: (Electrically Actuated)

              Drum brakes are commonly used on automobile rear wheels. They operate by forcing the friction-lined brake shoes against the inner surfaces of the rotating drums. A drum brake has two brake shoes, a piston, an adjuster mechanism, and an emergency brake mechanism and springs. The shoes expand against the inside surface of the brake drum and slow the wheel down. The harder the linings are forced against the brake drum, the higher the braking force that is applied.

              Many drum brakes are self-actuating, which means that shoe mounting can be designed to assist in their own operation. The self-actuating mechanism uses a wedging action to assist the lining to grip the rotating drum when the brakes are applied. This extra braking force allows drum brakes to use a smaller piston than disc brakes. The springs are used to pull the shoes away from the drum when the brake is released, as well as to help hold the brake shoes in place and return the adjuster arm after it actuates.

              Single leading shoe designs use a single wheel cylinder with two pistons. As the brakes are applied, both shoes (leading and trailing) press against the brake drum. The leading shoe is self-actuating, while the trailing shoe is forced off the drum. This arrangement works well going forward and reverse. Twin leading shoe designs have an actuator for each brake shoe

               Dual-servo designs use a single wheel cylinder with two pistons with a high self-actuating force. Since the lower ends of the shoes are linked but not firmly anchored to the backing plate, the shoe floats within limits. As brakes are applied, both shoes are carried around the drum, until the secondary shoe contacts the anchor pin and the self-actuating force of the primary shoe is transferred to the secondary shoe through their lower linkage. Force is applied to the secondary shoe from both ends, causing the wheel to slow. This design is common on rear wheels and it works in both the forward and reverse direction.

               For the drum brakes to function correctly, the brake shoes must remain close to the drum without touching it. As the shoes wear down, they can get too far away from the drum and the piston will require more fluid to travel that distance. To correct this, an automatic adjuster is used to fill the gap created as the brakes wear.

iii) Disc Brakes: (Electrically Actuated)

               Disc brakes consist of a caliper that squeezes brake pads against a rotating disc. They can be used on all four wheels of a vehicle or on the front brakes in conjunction with rear drum brakes. The most common type of disc brake is the single-piston floating caliper. The main components of this type are the brake pads and the caliper, which contains a piston; and the rotor, which is mounted to the hub. On driving wheels, the disc is mounted on the driving axle and may be held in place by the wheel.

             The brake caliper system is attached to the vehicle axle housing or suspension and the brake is usually attached as close to the wheel as possible. When no current is flowing in the coil, the motor is braked by two compression springs squeezing the brake pads and the brake rotor together. Friction between the pads and rotor slows the disc down. When current flows into the core, it counteracts the piston force, pulling the brake pads towards it, and the brake is released. 

              A lot of friction is generated during braking, and this creates heat in the system. Since the brake parts must be able to withstand high temperatures and are often exposed to air and vented, cooling is much faster than for drum brakes.

The single-piston floating caliper disc brake is self-centering and self-adjusting. Self-centering means that the caliper can slide from side to side so it will move to the center each time the brakes are applied. The pads always stay in light contact with the rotor so less force is needed to engage the brakes.

iv) Cone Brakes: (Electrically Actuated)

              Cone brakes include a cone that is lined with heat- and wear-resistant material that presses against a mating cup surface. They have a cup (female) and a cone (male), which is lined with a heat and wear-resistant friction material. During actuation, the cone is pressed against the mating cup surface. Cone brakes are not commonly used.