TECHNICAL SEMINAR ONPNEUMATIC BRAKING SYSTEM

PRSENTED BY:

MADAN KUNWAR1SJ11ME047

Department of Mechanical EngineeringS.J.C institute of Technology

Chickballapur-5621012014-2015

BRAKE:

A brake is a device by means of which frictional resistance is

applied to a moving machine member, in order to retard or stop the motion of a machine.

A brake is a mechanical device which inhibits motion, slowing or

stopping a moving object or preventing its motion.

Most commonly brakes use friction between two surfaces pressed together to convert the kinetic energy of the moving object into heat to slow down the motion of vehicle.

INTRODUCTION

A brake which uses air as working fluid is a pneumatic brake.The system actuated to apply this phenomenon is known as Pneumatic Brake System.

An pneumatic brake or a compressed air brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad needed to stop the vehicle.

George Westinghouse first developed pneumatic brakes for use in railway service. He patented a safer air brake on March 5, 1872. Westinghouse made numerous alterations to improve his air pressured brake invention, which led to various forms of the automatic brake used in modern vehicles for more safer and advance brakeing system.

In the early 20th century, after its advantages were proven in railway use, it was adopted by manufacturers of bus ,trucks and heavy road vehicles.

PNEUMATIC BRAKE SYSTEM

AIR COMPRESSO

R

AIR COMPRESSOR GOVERNOR

AIR DRYER

AIR STORAGE

TANKS

THE BRAKE PEDAL

DIRT COLLECTOR

BRAKE PIPE

AUXILARY RESERVOIR

BRAKE CYLINDER

BRAKE BLOCK

TRIPLE VALVE

COMPONENTS OF PNEUMATIC BRAKING SYSTEM

BLOCK DIAGRAM OF PNEUMATIC BRAKING SYSTEM

•The air compressor pumps air into the air storage tanks (reservoirs). The air compressor is connected to the engine through gears or a V-belt.

AIR COMPRESSOR

•The governor controls the air compressor which pump air into the air storage tanks (590 kpa - 900 kpa).

AIR COMPRESSOR

GOVERNOR

•An air dryer is used to take the moisture out of the air, so that water condensation will not build up in the air storage tanks and cause the brakes to fail, such as when the water freezes in the winter.

AIR DRYER

•Air storage tanks are used to hold compressed air.The tanks will hold enough air to allow the brakes to be used several times even if the compressor stops working.

AIR STORAGE

•The brakes are applied by pushing down the brake pedal (foot valve). The harder you push down on the pedal, the more air pressure is applied from the storage tanks into the brake chambers.

BRAKE PEDAL:

•It is placed in the brake pipe line at a point from where a branch is taken off to the triple valve.

DIRT COLLECTOR

•Brake cylinder is provided for actuating the brake rigging for the application and release of brakes.

BRAKE CYLINDER

•For application and release of brakes the brake pipe pressure has to be reduced and increased respectively with the help of driver's brake valve. During these operations the triple valve is used.

TRIPLE VALVE

Brake system that is based upon a design Air patented by George Westinghouse on March 5 1872. The Westinghouse Air Brake Company (WABCO) was subsequently organized to manufacture and sell Westinghouse invention which has been universally adopted.

Compressed air from compressor passes through the valve and maintains its pressure. This air is stored in the reservoir. And from the reservoir it goes to the Brake Chambers through many brake valves. In the brake chamber this pneumatic force is converted into the mechanical force and then it is converted into the rotational torque by the slack adjuster, which is connected to S-cam. This torque applies air brakes which is used to slow down the motion of the veichle.

WORKING OF PNEUMATIC BRAKE SYSTEM

Charging stage

Application Stage

Release stage.

Braking is done into three stages:

During this stage, brake pipe is charged to 5kg/cm2 pressure which in turn charges control reservoir and auxiliary reservoir to 5 kg/cm2 pressure via distributor valve.

At this stage brake cylinder gets vented to

atmosphere through passage in Distributor valve and there is no application of brake in the stage.

Charging Stage:

For application of brakes, the pressure in brake pipe has to be dropped. This is done by venting air from driver’s brake valve.

Reduction in brake pipe pressure positions the distributor valve in such a way that the control reservoir gets disconnected from brake pipe and auxiliary reservoir gets connected to brake cylinder.

The magnitude of braking force is proportional to reduction in brake pipe pressure which is done by the application of force on the brake pedal.

Application Stage :

Schematic Diagram of application stage

For releasing brakes, the brake pipe is again charged to 5 kg/cm2 pressure by compressor through driver’s brake valve.

This action positions distributor valve in such a away that auxiliary reservoir gets isolated from brake cylinder.

Brake cylinder is vented to atmosphere through distributor valve and thus brakes are released.

Release stage :

Schematic Diagram of release stage

Service Brake,

Parking Brake

Emergency Brake.

The air brake system is actually three separate systems :-

SERVICE BRAKE: This system applies and releases the brakes when the

driver pushes/releases the brake pedal. Pushing the brake pedal, opens a valve to let air flow from the air tank through the airlines to a brake chamber.

PARKING BRAKE : Parking brake releases air from the brake chamber

which allows the brake spring to expand and forces the pushrod out which pushes a slack adjuster that turns the camshaft, twisting the S-Cam and forcing the brake linings against the brake drum.

EMERGENCY BRAKE:

When there is insufficient air in the system to keep the spring in the chamber restrained, the emergency brakes automatically engage. When air pressure falls below 420 kpa, a low pressure warning light will come on along with an audible buzzer. If air pressure continues to fall, the emergency brake will automatically apply when air pressure drops to 140-310 kpa. The fail safe engineering of air brakes will not allow you to control activation of the emergency brake so look for a safe place to pull off the roadway as soon as the low pressure warning activates.

Air is available everywhere in atmosphere so the brake system can never run out of its operating fluid.

Air doesnot corrode the metals so the life of pneumatic brake is more.

Air line couplings are easier to attach and detach than hydraulic lines there is no danger of letting air into a pneumatic circuit.

Pneumatic brake has got emergency brake which gets activated when the service brake failes, so it is very safe.

Air brakes are effective even with considerable leakage, so an air brake system can be designed with sufficient fail-safe capacity to stop the vehicle safely even when leaking.

ADVANTAGES

If the brakes are applied before recharging has been completed, a larger brake pipe reduction will be required in order to achieve the desired amount of braking effort.

If the brake pipe pressure is too low due to an excessive no. of brake applications, an emergency application will not produce a large enough volume of air flow to trip the triple valves, leaving the engineer with no means to stop the vehicle.

This system is complicated and needs trained person to use it.

LIMITATION

The pneumatic brake is mainly used in large vehicles such as trucks, buses, trailers, and semi-trailers in addition to their use in railway train.

APPLICATION

Operation of pneumatic brakeis different from more common hydraulic systems,so most people require additional training and licensing in order to legally drive any vehicle using an air brake system.

Driving a vehicle with air brakes requires basic knowledge of proper maintenance as well. A driver should have knowledge to inspect the air pressurization system prior to driving and make sure all tanks are in working order.

DRIVING TECHNIQUE AND LICENSING

Brakes are the parts of the vehicle that absorb the energy generated by a vehicle in motion in order to stop it. Pneumatic brakes became popular because of their tremendous stopping power and long life as compared to hydraulic system. In order to do this, a system with several components with prpoer functioning is required. Air provides a simple outlet to accomplish this task. Thought the pneumatic brake is complicated to use and training has to be provided for its efficient use because of its tremendous power and its effiectiveness it is very usedful in large vehicles such as trucks, buses, trailers, and semi-trailers in addition to their use in railway train.

CONCLUSION

Bennett, Sean (2010). Heavy Duty Truck Systems, 5th Ed. USA: Cengage Learning. p. 907. ISBN 1435483820. State of California, Copyright 2003, California Commercial Driver Handbook, Sec.

Mechanics Corner: Understanding air brake systems. Types of Automotive Braking Systems S .Selvamani, Brake System Engineering, Sundaram Clayton limited,

Chennai, (1996) S.F. Williams and R.R. Knipling, "Automatic slack adjusters for heavy

Vehicle air brake systems," Research Report DOT HS, vol. 807, pp. 724, 1991.

New Brunswick Department of Public Safety, "Air brake manual," [On¬ Line]. Available: http://www.gnb.ca/0276/vehicle/pdf/anual-e.pdf, accessed May 2008

S.C. Subramanian, S. Darbha, and K.R. Rajagopal, "Modeling the Pneumatic subsystem of a scam air brake system," Journal of Dynamic Systems, Measurement, and Control, vol. 126, pp. 36, 2004.

REFERENCES