Ceramic Disc Brakes: Presented By,

CERAMIC DISC BRAKES

Presented by, CH.DURGARAO 12671A0366

INTRODUCTION

Today’s technology is in need for speed, also safety as well, for that deceleration is needed engines of max efficiency for maintaining the speed & brakes of latest technology is used.  Brake system are required to stop the vehicle within the smallest possible distance. By converting kinetic energy into heat energy which is dissipated to atmosphere.  For coping up with today’s speed, new materials are introduced in the manufacture of brakes. 

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In my seminar, I am introducing to you the ceramic disc brakes. Cast iron is extensively used as the material for manufacturing disc brakes. This is much heavier and thus reduces initial acceleration and causes more fuel consumption. For reducing these effects, we use ceramic brakes.

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The ceramic disc brakes possess the following advantages:

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Its weight is half the weight of conventional disc brakes.

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It increases the fuel efficiency of the vehicle.

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It functions well in wet conditions as well.

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The major disadvantage is its cost.

MAIN REQUIREMNTS 

The brakes must be strong enough to stop the vehicle within the minimum possible distance in an emergency. But this should also be consistent with safety. The driver must have a proper control over the vehicle during emergency braking and the vehicle must not skid.

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The brakes must have good antifade characteristics and their effectiveness should not decrease with constant prolonged application.

STOPPING DISTANCE OF A VEHICAL DEPENDS

Vehicle speed  Condition of the road surface  Condition of tyre tread  Coefficient of friction between the tyre tread and the road surface  Coefficient of friction between the brake drum/disc and brake lining/friction pad  Braking force applied by the driver 

TYPES OF BRAKES

Purpose Construction Method of Extra actuation braking effort Service brakes Parking brakes

Drum brakes Disc brakes

Mechanical brakes Hydraulic brakes Electric brakes Air brakes

Servo brakes Power operated brake

DISC BRAKE- CONSTRUCTION

DISC BRAKES

a disc brake consists of a cast iron disc bolted to the wheel hub and a stationary housing called caliper.  The caliper is connected to some stationary part of the vehicle, like the axle casing or the stub axle and is cast in two parts, each part containing a piston.  In between each piston and disc there is a friction pad held in position by retaining pins, spring plates etc., passages are drilled in the caliper for the fluid to enter or leave each housing. These passages are also connected to another one for bleeding. 

When the brakes are applied hydraulically actuated pistons move the friction pads into contact with the disc, applying equal and opposite forces the later.  On releasing the brakes the rubber sealing rings act as return springs and retract the pistons and the friction pads away from the disc 

CONSTRUCTIONAL FEATURES Two types brake discs are generally used the solid type and the ventilated type. The ventilated type more efficient since it provides better cooling. But they are thicker and heavier than solid type, they are liable to wrap at severe braking conditions, the dirt accumulates in the vents which affects cooling and apart produces wheel imbalance.  The discs of the brakes are made of pearlite gray cast iron. The material is cheap and has good antiwear properties.Their main drawback is the non uniform frictional behavior. 

The other materials used for the manufacture of disc are 1. Aluminium 2. Ceramic  Obviously, cast-iron disc is the heaviest part of a brake - about 8 kg each, or 32 kg per car. Aluminium alloy discs are used in the Lotus Elise. Though light, they were less resistant to heat and fade.  In contrast, carbon-fiber disc is most heat-resisting yet is by far the lightest, however, it requires very high working temperature, and otherwise braking power and response will be unacceptable. 

Ceramics are inorganic, non-metallic materials that are processed and used at high temperatures. They are generally hard brittle materials that withstand compression very well but do not hold up well under tension compared to the metals.  They are abrasive-resistant, heat resistant and can sustain large compressive loads even at high temperatures. The nature of the chemical bond in the ceramics is generally ionic in character 

COMPARISON B/W CERAMIC DISC BRAKES AND CONVENTIONAL DISC BRAKES

Until now brake discs have been made up of grey cast iron, but these are heavy which reduces acceleration, uses more fuel and has a high gyroscopic effect.  Ceramic disc brake weight less than carbon/carbon disc but have same frictional values, used in Formula1 racing cars etc.  CDB good at wet conditions but carbon/ carbon disc fails in wet conditions. 

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Weight – CDB are 61% lighter, reduces 20kg of car, apart we can save the fuel, resulting in better mileage. Improve the shock absorber and unsprung masses. We can add more safety features instead of the current weight.

MANUFACTURE OF CERAMIC DISC BRAKE In earlier days disc brakes were made from conventional brittle ceramic material.  Daimler Chrysler made carbon fiber reinforced brake discs which avoid the brittleness problem. In the earlier days, long carbon fibers were used. Later the use of short carbon fibers increased the efficiency.  short carbon fibres + carbon powder + resin mix(at1000 DC, sintering) = stable carbon frame work.  This carbon fibers are in carbon matrix. Once cooled this material can be ground like wood and the break disk obtains its final shape. 

Together with silicon the ground break disk blank is then inserted into the furnace a second time. The pores in the carbon framework absorb the silicon melt like a sponge; the fibers themselves remain unaffected by this process.  The ceramic material is created when the matrix carbon combines with liquid silicon. This fiber reinforced ceramic material cools over night and the gleaming dark grey break disk is ready  Resins : thermo plastics resins and thermo setting resins. 

PORSCHE CERAMIC DISC BRAKES (PCCB) After a long period of research and tests Porsche has developed new high performance disc brakes, PCCB (Porsche Ceramic Composite Brakes). Porsche has succeeded as the first car manufacturer in the world to develop ceramic brake discs with involute cooling ducts for an efficient cooling. The new brake system offers a substantial improvement in the car braking technology.  Instead, the Porsche Ceramic Composite Brake ensures maximum deceleration from the start without requiring any particular pressure on the brake pedal. And the new brake system is just as superior in its response under wet conditions 

PORSCHE CERAMIC DISC BRAKES (PCCB) 

Porsche has developed new high performance disc brakes, (PCCB). CDB with the involute cooling ducts for an efficient cooling. Offers braking response, fading stability, weight & service life. Does not require substantial pedal forces or any technical assistance.

PCCB ensures maximum deceleration from without any particular pressure on the brake pedal. It response under wet condition. New braking linings cannot absorb water. Cross drilled brake discs help to optimize response of the brakes also in wet weather.  The process involves of carbon powder, resins and carbon fibres in a furnace to about 1700DC is a high vacuum process 

ADVANTAGES & DISADVANTAGES

50% lighter than metal disc brakes reduces 20kg of car. In the case of train 36 disc brakes saving amount to 6 tons . Apart from saving fuel also reduce unsprung masses with a further improvement of shock absorber response & behavior.  High frictional values in deceleration process Porsche- 100 to 0 km in 3 sec. Daewoo’s Nexia- 100 to 0 km in 4 sec.  Brake temperature.  Resistance up to 2000 DC.  Still runs after 300000 km need not change CDB. 

No wear, maintenance free and heat and rust resistant even under high oxygen concn.  Heavy commercial can be braked safely over long distance without maintenance. 

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DISADVANTAGES

High initial cost and high cost of production.  As the advantages listed above we can hope CDB will work out to be cheaper in the future. 

APPLICATIONS

FORMULA1- in mid 90’s French sports car specialist Venturi.  Porsche 911 turbo- with a top speed of 305 km/h and acceleration from rest to 100 km/h in 4.2s. Its engine 3.6 L with 420 hp max torque 560 Nm is still running with PCCB.  911GT2- and Mercedes Benz’s futuristic vision GST is going to reinforce CDB . 

CONCLUSION 

CDB due to its advantages over the conventional brake disc are going to be the brake disc for cars in the future. With the success of Porsche turbo car, many other racing cars and commercial vehicles are going to implement CDB in cars.