Abstract The vacuum brake is a braking braking system system employed on trains trains and and introduced in the midmid-18 1860 60s. s. A vari varian ant, t, the the auto automa mati ticc vacu vacuum um brak brakee syst system em,, beca became me almo almost st universal in British train euipment and in those countries in!luenced by British practice. This braking system uses a vacuum pump !or creating vacuum in the brake pipe. The integral construction o! the brake cylinder uses this vacuum reservoir !or the application o! brakes. "o#adays most o! the light vehicles are !itted #ith vacuum-assisted hydraulic braking system #here vacuum is created !rom the engine #hich reduces the driver e!!ort on !oot pedal. The vacuum braking syst system em #as #as modi modi!i !ied ed !rom !rom abov abovee said said reaso reasons ns and and the the same same #as #as test tested ed !or !or implementation in both light and heavy vehicles. $n this #ork, vacuum is created and used !or the application o! brakes. The system operation is someho# similar to air braking system. The main di!!erence #ith air brake system is that vacuum is used instead o! compressed air. The design and modi!ied system also includes the %acuum brake system i.e., the loss o! vacuum #ill cause the brake to be applied due to spring !orce. Brakes are mechanical devices #hich increases the !rictional resistance that retards the turning motion o! the vehicle #heels. $n vacuum assisted hydraulic brake system, a constant vacuum is maintained in the brake booster by the engine. &hen the brake pedal is depressed, a poppet valve opens and air pushes into the pressure chamber on the driver's side o! the booster. %acuum braking system uses the vacuum !or the application o! brakes.
Introduction
$n the earliest days o! rail#ays, trains #ere slo#ed or stopped by the application o! manually applied brakes on the locomotive and in brake vehicles through the train, and later by steam po#er brakes on locomotives. This #as clearly unsatis!actory, but the technology o! the time did not easily o!!er an improvement. A chain braking system #as developed, reuiring a chain to be coupled throughout the train, but it #as impossible to arrange eual braking e!!ort do#n the length o! the train. A ma(or advance #as the adoption o! a vacuum braking system in #hich !le)ible pipes #ere connected bet#een all the vehicles o! the train, and brakes on each vehicle could be controlled !rom the locomotive. The earliest pattern #as a simple vacuum brake, in #hich vacuum #as created by operation o! a valve on the locomotive* the vacuum actuated brake pistons on each vehicle, and the degree o! braking could be increased or decreased by the driver. %acuum, rather than compressed air, #as pre!erred because steam locomotives can be !itted #ith e(ectors, #hich are simple venturi devices that create vacuum #ithout the use o! moving parts. +o#ever, the simple vacuum system had the ma(or de!ect that in the event o! one o! the hoses connecting the vehicles becoming displaced by the train accidentally dividing, or by careless coupling o! the hoses, or other#ise the vacuum brake on the entire train #as useless. The automatic vacuum brake had been developed it #as designed to apply !ully i! the train becomes divided or i! a hose becomes displaced, but opposition on the grounds o! cost particularly by the /"& and its chairman ichard oon to the !itting o! the automatic type o! brake meant that it took a serious accident at Armagh in 1882 be!ore legislation compelled the automatic system. The train #as !itted #ith the simple vacuum brake, #hich #as useless on the disconnected portion o! the train.
CLASSIFICATION OF BRAKES
On the Basis of Method of Actuation (a) Foot brake (also called service brake) operated by foot pedal. (b) Hand brake – it is also called parking brake operated by hand.
On the Basis of Mode of Operation (a) Mechanical brakes (b) Hydraulic brakes (c) Air brakes (d) acuu! brakes (e) "lectric brakes.
On the Basis of Action on Front or #ear $heels (a) Front%&heel brakes (b) #ear%&heel brakes.
On the Basis of Method of Application of Braking 'ontact (a) nternally – epanding brakes (b) "ternally – contracting brakes.
Air Brakes Air brakes are applied by the pressure of co!pressed air. Air pressure applies force on brakes shoes through suitable linkages to operate brakes. An air co!pressor is used to co!press air. *his co!pressor is run by engine po&er. acuu! Brakes acuu! brakes are a piston or a diaphrag! operating in a cylinder. For application of brakes one side of piston is sub+ected to at!ospheric pressure &hile the other is applied vacuu! by ehausting air fro! this side. A force acts on the piston due to di,erence of pressure. *his force is used to operate brake through suitable linkages. "lectric Brakes n electrical brakes an electro!agnet is used to actuate a ca! to epand the brake shoes. *he electro!agnet is energi-ed by the current o&ing fro! the battery. $hen o& of current is stopped the ca! and brake shoes return to their original position and brakes are disengaged. "lectric brakes are not used in auto!obiles as service brakes. *here are t&o !ain functions of brakes/ (a) *o slo& do&n or stop the vehicle in the shortest possible ti!e at the ti!e of need. (b) *o control the speed of vehicle at turns and also at the ti!e of driving do&n on a hill slope.
Construction of vacuum braking systm
%acuum braking system as sho#n in !ig consists o! brake cylinder, compressor, vacuum reservoir, direction control valve, !lo# control valve, brake hoses, brake linkages, drum brake and !oot brake pedal.
Direction control valve
a
b
The direction control valve is as sho#n in !ig a and b are used in this #orks to change the direction o! air !lo# to and !rom the cylinder. The moving parts in the directional control valve #ill connect and disconnect internal !lo# passages #ithin the valve body. This action results in control o! air!lo# direction. The typical directional control valve consists o! a valve body #ith !our internal !lo# passages #ithin the valve body and a sliding spool. 3hi!ting the spool alternately connects a cylinder port to supply pressure or e)haust port. &ith the spool in the #here the supply pressure is connected to passage A and passage B connected to the e)haust passage, the cylinder #ill e)tend. Then #ith the spool in the other e)treme position, 3upply pressure is connected to the e)haust port, no# the cylinder retracts. &ith a directional control valve in a circuit, the cylinder piston rod can be e)tended or retracted and #ork #ill be per!ormed. The #orking o! direction control valve is sho#n in !ig a and b.
F!o" contro! va!v
A o& control valve is as sho&n in 0g consist of a disc &hich opens and closes the t&o &ay connection bet&een the 123 valve and brake cylinder. Operation is si!ilar to that of a buttery valve4 &hich allo&s for 5uick shut o,. *he disc is positioned in the 6%shaped pipe4 passing through the disc is a rod connected to an actuator on the outside of the valve. *he need of o& control valve is for partial braking. $hen the valve is closed4 the disc is turned so that it co!pletely blocks o, the passage&ay bet&een the at!ospheric path and brake cylinder.
#rum brak
7ru! brake syste! !ay be of either design in practice4 but the t&in leading design is !ore e,ective. *his design uses t&o actuating cylinders arranged in a !anner4 so that both shoes &ill utili-e the self%applying characteristic &hen the vehicle is !oving for&ard. *he brake shoes pivot at opposite points to each other. *his gives the !ai!u! possible braking &hen !oving for&ard4 but is not so e,ective &hen the vehicle is in reverse !ode. *he &heel cylinder and retractor spring of the dru! brake is re!oved and suitable co!pression spring is 0ed. *he spring is placed in bet&een the t&o cups so that it seats properly. *he dru! brake asse!bly is sho&n in 0g
Design of brake cylinder
"ach &heel has one brake cylinder. *he at!ospheric airs in brake cylinder4 connecting hoses4 vacuu! reservoir are re!oved by suction force created by the co!pressor.
#sign of brak $da! !inkag
*he linkage is a !echanical lever &ith one side pivoted to the pedal and the other end to the 123 valve lever. *he return force is applied by torsion spring &hich is hinged to the fra!e. *he brake pedal is also linked &ith another valve kno&n as o& control valve &hich functions like as buttery valve
Design of L-shaped link rod A !echanical link rod is an asse!bly of bodies connected together to !anage forces and !ove!ent. *he !ove!ent of a body4 or link4 is studied using geo!etry4 by considering link as rigid.
%orking of &acuum Braking Systm
acuu! brake cylinder in running position/ the vacuu! is the sa!e above and belo& the piston Air at at!ospheric pressure fro! the train pipe is ad!itted belo& the piston4 &hich is forced up $hen the driver pushes the brake pedal slo&ly then the o& control valve opens slightly to the at!osphere. 8oss of vacuu! causes the brake to be applied due to spring force. $hen the o& control valve opens fully then alternatively the direction control valve lever is !oved to for&ard direction. *he direction of o& is changed and at!ospheric air enters through the ehaust port of direction control valve to piston cap end. 7ue to pressure di,erence the piston !oves back&ard &ith vacuu! and spring force. *he !ove!ent of link rod attached &ith piston rod releases the ca! to nor!al position &hich !akes internal resistances for the brake shoes against dru!. *his applies the brake.
'a! and link !echanis! after during brake
'a! and link !echanis! the release brake $hen driver releases the brake pedal4 the valve lever co!es back to initial position. *he direction of o& is again changed and at!ospheric air enters through the ehaust port of direction control valve to piston rod end. 7ue to the pressure di,erence4 the piston !oves for&ard &ith vacuu!. *he !ove!ent of link rod attached &ith piston rod t&ists the ca! and co!presses the spring to provide enough clearances bet&een brake shoes and the dru!. *his releases the braking action.
Effct of air $rssur on s$ring tnsion
As the air pressure increases spring tension decreases. *he spring is held in the co!pressed state by the vacuu! generated by the suction e,ect of the co!pressor. As the spring is released fro! the co!pressed state4 the brake gets applied.
9pring *ension vs. air pressure
Effct of air $rssur on brak forc
*he brake force increases &ith increase in air pressure. *he increase in pressure per!its the spring to be released fro! its co!pressed state4 allo&ing the brake shoe to press upon the brake dru! leading to application of brake.
Effct of s$ring tnsion on brak forc
t is apparent that &ith the increase in spring tension4 the brake force reduces. As !entioned in the previous discussion that the spring tension is !ai!u! since4 it is in the co!pressed state by the suction created by the vacuu!.
Advantags of &acuum Braking systm
9i!ple in design. Ability to get partial release4 so!ething the pneu!atic brake could not do &ithout additional e5uip!ent. :reater a!ount of safety because the vacuu! loss results in the braking of the vehicle. Highly reliable in the case of rail &agons. 'o!pressed air can be produced. 8ess noise. acuu! brakes are also fail safe since the vacuu! is used for applying the brake.
Limitations
*he practical li!it on the degree of vacuu! attainable !eans that a very large brake piston and cylinder are re5uired to generate the force necessary on the brake blocks "istence of vacuu! in train pipe can cause debris to be sucked in 'onsiderable volu!e of air has to be ad!itted to the train pipe to !ake a full brake application4 and a considerable volu!e has to be ehausted to release the brake &hile the air is traveling along the train pipe4 the brake pistons at the head of the train have responded to the brake application or release4 but those at the tail &ill respond !uch later4 leading to undesirable longitudinal forces in the train.
Rfrnc
$. Bartlett4 ;assenger vehicle Braking ;erfor!ance &ith a 7isabled acuu! ;o&er Booster4 (<==>)4 9A" paper4 =>?=@ 6. :oto4 Atsushi 6asuda and 9atoshi shida4 Brake Master 'ylinder for 9ecure Brake Feel and !proved 9yste! Failure ;erfor!ance4 (<==>)4 9A" paper 3??1%?<%11?@ B.;. 'hin!aya and #aul4 :. 8. #aul4 Modular design and testing for anti% lock brake actuation and control using a scaled vehicle syste!4 nternational ournal of ehicle 9yste!s Modelling and *esting4 ol. 34 Co.@4 (3??>)4 pp. @<< % @3>.
