Anbalagan . R, Jancirani .J, Venkateshwaran. N / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.907-916907 | P a g e‘‘Design and Modification of vacuum braking system”Anbalagan . R (*), Jancirani .J(**), Venkateshwaran. N(***)* Department of Automobile Engineering, Rajalakshmi Engineering College, Chennai –602105. India.** Madras Institute of Technology, Chennai-600044.India.***Department of Mechanical Engineering, Rajalakshmi Engineering College, Chennai -602105. India.AbstractVacuum brakes are first used in place ofthe air brake in railway locomotives. Thisbraking system uses a vacuum pump for creatingvacuum in the brake pipe. The integralconstruction of the brake cylinder uses thisvacuum reservoir for the application of brakes.Nowadays most of the light vehicles are fittedwith vacuum-assisted hydraulic braking systemwhere vacuum is created from the engine whichreduces the driver effort on foot pedal.The vacuum braking system wasmodified from above said reasons and the samewas tested for implementation in both light andheavy vehicles. In this work, vacuum is createdand used for the application of brakes. Thesystem operation is somehow similar to airbraking system. The main difference with airbrake system is that vacuum is used instead ofcompressed air. The design and modified systemalso includes the Vacuum brake system i.e., theloss of vacuum will cause the brake to be applieddue to spring force.Key words: Air braking system, Fail safecondition, Heavy vehicle, Hydraulic brake, Lightvehicle, Vacuum braking system .1. IntroductionBrakes are mechanical devices whichincreases the frictional resistance that retards theturning motion of the vehicle wheels. In vacuumassisted hydraulic brake system, a constant vacuumis maintained in the brake booster by the engine.When the brake pedal is depressed, a poppet valveopens and air pushes into the pressure chamber onthe driver’s side of the booster.Vacuum braking system uses the vacuumfor the application of brakes. Many research workswere carried out in the area of vacuum brakes. Someof them are briefly explained below.Bartlett  worked on the vacuum-poweredbrake booster in a passenger vehicle becomesdisabled, the brake force gain of the system isreduced significantly, and the brake pedal forcerequired to lock the tires increases beyond the abilityof some adults. In such cases, the maximum brakingdeceleration achieved by those individuals will besomething less than the upper boundary as definedby available traction.Goto et al  developed the optimal braking effectand feel for the brake master cylinder for the heavyvehicles. In this, braking effect was enhanced duringa vacuum failure condition by operating the smallerbore. Thus, the vacuum failure detection and theincrease output pressure are performedmechanically. By this development, it hascontributed to the design of the optimal brakesystem.Shaffer and Alexander  determinewhether the performance-based brake testingtechnologies can improve the safety of the highwaysand roadways through more effective or efficientinspections of brakes of the road commercialvehicles. However, the performance-basedtechnologies were able to detect a number of brakedefects that were not found during visual inspection.Saeed Mohammadi and Asghar Nasr found that for the heavy haul trains. Coupled often,there is no alternative to the air brake system. Inthese trains, the cars at the end of the train brake afew seconds later than those at the front. The timedelay between the braking of the adjacent carsdepends very much on the transmission speed of thepressure wave (brake signal) in the main brake pipe,which is about 10-25% less than the speed of soundin free air. The later braking of the cars at the rear ofthe trains means that the rear cars run into the frontcars, producing large compression forces on thebuffers and couplings. These compression forces arelongitudinal in nature and are considered to beresponsible for large amount of expenses regardingrolling stock and track sub- and super-structuresrepairs, as well as the deterioration of safetyoperation of the trains.Chinmaya and Raul  suggested a uniqueof decoupling feature in frictional disk brakemechanisms, derived through kinematic analysis,enables modularised design of an Anti-lock BrakingSystem (ABS) into a sliding mode system thatspecifies reference brake torque and a tracking brakeactuator controller. Modelling of the brake actuation,vehicle dynamics, and control design are describedfor a scaled vehicle system. The overall controlscheme is evaluated by hardware-in-the loop testingof the electromechanical brake system.Bharath et al  deals with nonlinearlumped multicapacity models with train pipecapacity and brake cylinder capacity lumpedseparately to predict pressure rise in the pneumatic
Anbalagan . R, Jancirani .J, Venkateshwaran. N / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.907-916908 | P a g ebrake cylinders for step the type of pressure input.The first model is a two-capacity system in which allthe brake cylinder capacitances and the entire pipeline capacitance are lumped separately. The secondmodel is multicapacity system in which the trainpipe capacitance between the brake cylinders ofadjacent wagon is lumped near the brake cylindercapacitance in each wagon separately. The thirdmodel is also of multicapacity type, similar to thesecond model, but it includes the effect of varyingbrake cylinder capacity in its formulation.Chen et al  took up the traditional purelyhydraulic braking pedal features the research object.The brake pedal control model of the regenerativebraking integrated system is established by usingtrajectory tracking control strategy. The simulationresults showed that, the model can achieve apredetermined vehicle brake pedal feel, and get thebrake demand and pedal feel demand by theresolving the brake pedal state motion. The researchalso provides a theoretical basis for the design ofregeneration brake pedal system for the electricvehicle and hybrid vehicle.Lie and Sung  investigated the brakingperformance and safety for a bicycle riding on astraight and inclined path. The equations of motionfor a wheel model as well as for the idealsynchronous braking are derived to acquire theshortest braking distance to improve the ridingstability. The optimal design of the bicycle brakingis obtained based on the simulation results withvarious bicycle geometries, ratios of brake force, androad friction.Park et al  attempt to establish ananalytical tool to evaluate the braking feel to helpoptimal design of brake systems. First, mathematicalmodels of brake systems are developed and areconfirmed through computer simulations. Second,mechanical impedance at brake pedal is modelledbased on the developed brake system models. Thebrake pedal feel is represented in the form ofimpedance surface. Third, to provide a guideline todesign optimal braking feel, relations between pedalforce, pedal stroke and vehicle deceleration areinvestigated. An expert test drivers evaluationprocess is modelled based on his subjective ratingsof brake systems. Moh Nasr  study of focused onthe noise generation by the actuation part of thebrake system, specifically the vacuum Mastervac. Inthis paper the noise types, their acoustic signaturesin both time and frequency, as well as the currentacoustic treatment impact, were discussed with theobjective of establishing a common and standardizedterminology.Yang and Hong  consider the brakingforce produced by tugboat has been scarcelyexamined and little data on the proper characteristicsof the braking force were obtained. In that work, thebraking force characteristics of tugboat-self inbraking condition are obtained and the relatedunstable phenomena is pointed out and analyzedaccording to the results of model experiments.Furthermore, some new understanding on thebraking operation using tugboat was predicted.Liang and Chon  modified the sliding controlwith variable control parameter was introduced toreduce the large change of pressure feedback in thehydraulic brake control process of automatedhighway vehicles. An average decay function wasused to smooth both the high and low frequencyoscillations of the desired diaphragm force andoutput force in the vacuum booster to remedy theoscillations generated by using the pushrod force atthe end-brake control. Simulation results indicatethat the variable parameter sliding controlsignificantly reduces the speed and space trackingerrors in the large brake processes, and the errorsexperienced during these processes are dominated bythe large brake pressure lag rather than the switchingdelay time between throttle and brake.2. Construction of vacuum braking systemVacuum braking system as shown in fig .1consists of brake cylinder, compressor, vacuumreservoir, direction control valve, flow control valve,brake hoses, brake linkages, drum brake and footbrake pedal.Fig .1 Vacuum braking systemDing et al  developed providing anefficient and reliable means of friction and pressureestimation algorithm, based on wheel speed signalsand control commands for hydraulic valve operation.Estimated results are achieved by comparing thesums of squared speed errors between the measuredwheel speeds and those based on the brake pressuremodel and wheel dynamics. Performance of thealgorithm is evaluated using ABS test data undervarious braking conditions.
Anbalagan . R, Jancirani .J, Venkateshwaran. N / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.907-916909 | P a g e2.1 Direction control valveThe direction control valve is as shown infig .2 (a) and (b) are used in this works to change thedirection of air flow to and from the cylinder. Themoving parts in the directional control valve willconnect and disconnect internal flow passages withinthe valve body. This action results in control ofairflow direction. The typical directional controlvalve consists of a valve body with four internalflow passages within the valve body and a slidingspool. Shifting the spool alternately connects acylinder port to supply pressure or exhaust port.With the spool in the where the supply pressure isconnected to passage A and passage B connected tothe exhaust passage, the cylinder will extend. Thenwith the spool in the other extreme position, Supplypressure is connected to the exhaust port, now thecylinder retracts. With a directional control valve ina circuit, the cylinder piston rod can be extended orretracted and work will be performed. The workingof direction control valve is shown in fig .2 (a) and(b).(a) (b)Fig .2 Working of direction control valve2.2 Flow control valveA flow control valve is as shown in fig.3consist of a disc which opens and closes the two wayconnection between the 3/2 valve and brakecylinder. Operation is similar to that of a butterflyvalve, which allows for quick shut off. The disc ispositioned in the Y-shaped pipe, passing through thedisc is a rod connected to an actuator on the outsideof the valve. The need of flow control valve is forpartial braking. When the valve is closed, the disc isturned so that it completely blocks off thepassageway between the atmospheric path and brakecylinder.Fig.3 Flow control valve2.3 Drum brakeDrum brake system may be of either designin practice, but the twin leading design is moreeffective. This design uses two actuating cylindersarranged in a manner, so that both shoes will utilizethe self-applying characteristic when the vehicle ismoving forward. The brake shoes pivot at oppositepoints to each other. This gives the maximumpossible braking when moving forward, but is not soeffective when the vehicle is in reverse mode.The wheel cylinder and retractor spring ofthe drum brake is removed and suitable compressionspring is fixed. The spring is placed in between thetwo cups so that it seats properly. The modifieddrum brake assembly is shown in fig.8. Flat shapedcam is made up of hard steel material is linked to therectangular shaped plate made up of steel sheet areattached with the top ends of brake shoes. The otherface of the cam is joined with L shaped link rodwhich is mounted with the piston rod end. Theprinciple of vacuum brake is based on the pressuredifference created in the actuator i.e. the brakereleased with a full vacuum and the brake appliedwith vacuum and spring force. The term “vacuum”is used to describe the region of pressure below oneatmosphere of pressure, also referred to as negativepressure. The pressure in the atmospheric is definedas 0.1 N/mm2and reducing atmospheric pressure tozero pressure creates a near perfect vacuum which ismeasured as 735 mm of mercury.The brakes are always in released conditionwith vacuum until the driver pushes the brake pedal.In this condition, position of piston is in cap end ofthe brake cylinder and cam is twisted forcompressing the spring which provides free rotationof drum. When the driver pushes the brake pedalslowly then the flow control valve opens slightly tothe atmosphere. Loss of vacuum causes the brake tobe applied due to spring force. When the flowcontrol valve opens fully then alternatively thedirection control valve lever is moved to forwarddirection. The direction of flow is changed andatmospheric air enters through the exhaust port ofdirection control valve to piston cap end. Due topressure difference the piston moves backward withvacuum and spring force. The movement of link rod
Anbalagan . R, Jancirani .J, Venkateshwaran. N / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.907-916910 | P a g eattached with piston rod releases the cam to normalposition which makes internal resistances for thebrake shoes against drum. This applies thebrake.Fig.4 shows the brake is applied condition.Fig.4 Cam and link mechanism after duringbrakeWhen driver releases the brake pedal, the valvelever comes back to initial position. The direction offlow is again changed and atmospheric air entersthrough the exhaust port of direction control valve topiston rod end. Due to the pressure difference, thepiston moves forward with vacuum. The movementof link rod attached with piston rod twists the camand compresses the spring to provide enoughclearances between brake shoes and the drum. Thisreleases the braking action. Fig.5 shows the brake inreleased condition.Fig.5 Cam and link mechanism the release brake2.4 Design and modification of components2.4.1 Dimension of brake drumMaterial Chosen : High carbonsteel (C95 steel)Physical properties of high carbon steel:Shear stress = 570 N/mm2Modulus of rigidity = 7.7 104N/mm2Force developed on brake shoe, F = P x AThe dimension of brake drum is shown in fig. 6Width of brake shoe, w = 39 mmRadius of brake drum, r = 115 mmArea of brake shoe, A =2= 16438 mm2Assume safe pressure, p = 0.20 N/mm2(From Design Data book)Force developed, F = 0.20 164384= 3288 NFig. 6 Dimensions of brake drum2.4.2 Design of compression springSpring was designed using standard formulae aslisted in the table.1.Table 1: Specification of spring parameterSpring parameters ValuesSafe pressure(p) 0.2 N/mm2Spring index(C) 4Wahl’s stress factor, Ks 1.40325Stress (y ) 570 N/mm2Standard size of wire diameter(d) 9 mmMean coil diameter(D) 36 mmDeflection(y) 20 mmStiffness(q) 164.4 N/mmNumber of active turns(n) 8Total number of turns(N) 10Solid length(Ls) 90 mmFree length(Lf ) 110 mmPitch(p) 12.22 mm
Anbalagan . R, Jancirani .J, Venkateshwaran. N / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.907-916911 | P a g eFig.7 Compression springFig.8 Modified Brake AssemblyAccording to this specification the required spring ispurchased. The manufactured spring is shown infig.7.After designing the compression spring, it isfitted in modified brake assembly as show in fig.18.104.22.168 Design of cam mechanismConsider the brake applied condition, the forcedeveloped by the piston rod to brake shoestransmitted through link rod and the cammechanism. The design of cam and links photoview is shown in fig.9.Fig.9 Design of cam and links2.4.4 Design of brake cylinderEach wheel has one brake cylinder. Theatmospheric airs in brake cylinder, connecting hoses,vacuum reservoir are removed by suction forcecreated by the compressor. The specifications ofbrake cylinder is shown in fig.10.The followingassumptions were made during the design of brakecylinder are listed in the table 2.Fig.10 Design of brake cylinderTable 2: Specification of brake cylinderProperties ValuesVacuum pressure 0.01 N/mm2Cylinder diameter D=4dAccording to the nearest standard diameter, cylindersize is taken as 200 mm.2.4.5 Design of brake pedal linkagesThe linkage is a mechanical lever with oneside pivoted to the pedal and the other end to the 3/2valve lever. The return force is applied by torsionspring which is hinged to the frame. The brake pedalis also linked with another valve known as flowcontrol valve which functions like as butterfly valve.The function of brake pedal is shown in fig.22.214.171.124 Design of L-shaped link rodA mechanical link rod is an assembly ofbodies connected together to manage forces andmovement. The movement of a body, or link, isstudied using geometry, by considering link as rigid.Material chosen: Steel rodAssume stress = 20 MPa= 20 N/mm2Load subjected = 3288 NCross sectional area, A = F/ A= 3288/204 d2= 164.4d = 14.46 mm= 15 mmOne end of the L shaped link rod is boltedwith the piston rod end of the brake cylinder and the
Anbalagan . R, Jancirani .J, Venkateshwaran. N / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.907-916912 | P a g eother end is pivoted with the cam mechanism. Thephoto view of fabricated link rod is shown in fig.11.Fig.11 Link rod2.4.7 FrameAll the components are assembled on theframe and it prevents the components from anymisalignment. The following components were usedfor the fabrication of vacuum brake system are listedin table 3, fabricated model photo view as show infig.12.Fig. 12 Fabricated models3. Results and discussion3.1 Effect of air pressure on spring tensionFig.13 shows the plot of spring tension Vsair pressure. Initially the spring tension is 3200 N at0.1 bar of air pressure. As the air pressure increasesin steps of 0.2 bar, reduce to approximately 1 N at 1bar air pressure, because of air pressure increases thespring tension decreases. The spring is held in thecompressed state by the vacuum generated by thesuction effect of the compressor. As the spring isreleased from the compressed state, the brake getsapplied.Fig.13 spring tension Vs air pressure3.2 Effect of air pressure on brake forceFig. 14 shows the plot of brake force Vs airpressure, the brake force increases with increase inair pressure. The increase in pressure permits thespring to be released from its compressed state,allowing the brake shoe to press upon the brakedrum leading to application of brake. From thegraph, it is clear that as the air pressure Increases insteps of 0.2 bar, the brake force increase to 10000 Nat 1 bar air pressure.Fig. 14 Brake force Vs air pressure3.3 Effect of spring tension on total forceFig.15 shows the total force Vs springtension, it is apparent that as the spring tensionincreases, the total force that is the normal forceacting on the contact point between the brake shoeand the brake drum decreases. The spring tension isthe indirect indicator of the state of the spring i.e.,whether the spring is compressed or extend. Fromthe graph, it is evident that, the total force is 20000N initially. As the spring tension increases in stepsof 500 N, the total force reduces to zero at 3300 Nspring tension.
Anbalagan . R, Jancirani .J, Venkateshwaran. N / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.907-916913 | P a g eFig. 15 Total pressure Vs spring tension3.4 Effect of spring tension on brake forceFig.16 shows the brake force Vs springtension. It is apparent that with the increase in springtension, the brake force reduces. As mentioned in theprevious discussion that the spring tension ismaximum since, it is in the compressed state by thesuction created by the vacuum. From the graph it isunderstandable that at the initial stage the brakeforce is 100000 N.As the spring tension increases insteps of 1000 N, the brake force reduces to 2000 Nat 3400 N spring tension.4. ConclusionsThe design and fabrication of a brakingsystem is a difficult and great task. The applicationof brakes using vacuum in automobiles was adifficult in the initial stages of the work. But it hasbeen successfully proved that such brake applicationis possible with fail-safe condition. By implementingthis idea on a heavy vehicle, it is better to replace themanually operated direction control valve withsolenoid operated direction control valve to reducedriver effort and also it will also work like a brakepedal switch.The main advantages offered by the vacuum brakingsystem are:• This system provides fail-safe condition.• Compressed air can be produced.• Less noise.Fig. 16 Brake force Vs Spring tension
Anbalagan . R, Jancirani .J, Venkateshwaran. N / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.907-916914 | P a g eReference W. Bartlett, Passenger vehicle BrakingPerformance with a Disabled VacuumPower Booster, (1997), SAE paper, 970946. Y. Goto, Atsushi Yasuda and SatoshiIshida, Brake Master Cylinder for SecureBrake Feel and Improved System FailurePerformance, (1997), SAE paper 2003-01-3304. S.J. Shaffer, and G.H. Alexander,Commercial Vehicle Brake Testing Part 2Preliminary Result of Performance-BasedTest Program, (1995), SAE paper, 952672. Saeed Mohammadi and Asghar Nasr,Effects of the power unit location on in-trainlongitudinal forces during brake application,International Journal of Vehicle SystemsModelling and Testing, Vol. 5, No.2/3,(2010), pp. 176 – 196. B.P. Chinmaya and Raul, G. L. Raul,Modular design and testing for anti- lockbrake actuation and control using a scaledvehicle system, International Journal ofVehicle Systems Modelling and Testing, Vol.2, No.4, (2007), pp. 411 - 427. S. Bharath, B.C. Nakra and K.N Gupta,Modelling and analysis of pneumaticrailway brake system, Applied mathematicalmodelling, 14, (1990), 58-66. Q. Chen, Guangju Xu, Jie Meng and HongyuJiao, Study on the brake pedal controlmodel for regenerative braking integratedsystem, International Journal of Electricand Hybrid Vehicles, Vol. 4, No.3, (2012),pp. 289 – 296. D. Lie and C.K Sung, Synchronous brakeanalysis for a bicycle, Mechanism andMachine Theory, 45 , (2010), 543-554. S. Park, Sangwoo Bae and Jang Moo Lee,Numerical evaluation of braking feel todesign optimal brake-by-wire system,International Journal of Vehicle Design,Vol. 37, No.1, (2005), pp. 1 - 23. Moh Nasr, Noise signatures of brake vacuumbooster and their acoustictreatment, International Journal of VehicleNoise and Vibration, Vol. 7, No.1, (2011),pp. 51 - 67. N. Ding, Guizhen Yu and Weida Wang,Estimation of brake pressure and tyre-roadfriction during ABS activation, InternationalJournal of Vehicle Design, Vol. 58, No.1,(2012), pp. 33 - 45. L.J Yang and B.G Hong, Experimentalstudy on braking force characteristicsof tugboat, Journal of hydrodynamics, 22(5),supplement: (2010), 343-348. H. Liang and K.T. Chong, (2003) Vehiclelongitudinal brake control using variableparameter sliding control, ControlEngineering practice11,(2003), 403-411.