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    hydraulic regenerative barking system hydraulic regenerative barking system Document Transcript

    • Chapter 1Introduction1.1 BackgroundA group of students senior to us worked on a system that can generate power usingweight force. Their work served as an inspiration, initially it was decided toimprove their work. Due to the some shortcomings the project turned out to bevery difficult to pursue, hence we had to look for something else in the samebracket of energy recovery. This quest finally led us to the idea of “HydraulicRegenerative Braking” or “Hydraulic Hybrid” (as compared to Electric Hybrid).Discussion of motion is incomplete without considering Friction. Friction ifunintentional can cause big loss of energy like in case of contacting surfaces whereit is highly undesirable, but if put to use intentionally it can be very handy like incase of automobile brake mechanism. Conventional braking mechanism ofautomobiles utilizes friction to overcome the momentum of vehicle. In case of“Friction Disk brakes” brake caliper comes in contact with the rotating disk,momentum possessed by the disk is consumed by the friction between the twocontacting surfaces. Almost all of the energy consumed by friction is lost toatmosphere in form of heat. Conventional friction brake mechanism thougheffective but is wasteful in terms of energy. Immense amount of precious workproduced by automobile engine is lost to friction and eventually heat. HRB(Hydraulic Regenerative Braking) is an approach towards recovering that energyand reusing it to gain the lost momentum back. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 1
    • 1.2 Energy situation in PakistanAccording to “Pakistan Energy Yearbook 2009” issued by HydrocarbonDevelopment Institute of Pakistan, Pakistan produced 62.6 MTOE energy in theyear 2008-09. Figure # 1.1 shows the supply of energy by source in year 2008-09and 2003-04. 70 Million TOE 60 7.07 4.76 50 6.82 Hydro & Nuclear 3.31 40 Coal 30.26 30 Gas 25.3 LPG 20 Oil 10 20.1 15.2191 0 2003-04 2008-09 Fig #1.1 Primary energy supplies by source (Pakistan) Source: Pakistan Energy Yearbook 2009SourcesOil: 32.1 % of the 62.6 MTOE energy consumed in Pakistan during year 2008-09was produced using Oil as fuel, which includes Petrol, Diesel, Furnace oil and allother variants. In year 2008-09 net indigenous production of Oil was 3.22 MTOEand the imports were 18.226MTOE.Gas: 48.3 % of 62.6 MTOE consumed in Pakistan was produced using Gas during year 2008-09.Gas is an indigenous product hence no imports were made.LPG: 0.6 % of 62.6 MTOE produced using LPG as fuel.Coal: 4.75 MTOE energy was produced using coal in year 2008-09, out ofwhich 1.67 MTOE was imported.Hydro and Nuclear: 7.074 MTOE energy was produced using Nuclearand Hydro energy. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 2
    • 1.3 Energy consumption in transportation (Pakistan)Transport sector is a major consumer of liquid fuel or Oil. It includes all roadtransport such as trucks, trawlers, cars, motor cycles and buses, trains, Airplanesetc. 0.5 In 5.4 2.1 0.4 42.3 Agriculture Transport Power Industrial Domestic 49.3 Other Govt.year 2008-09 net indigenous production of Oil was 3.22 MTOE and the imports sector (Pakistan) Fig #1.2 Petroleum products consumption by Source: Pakistan Energy Yearbook 2009were 18.226MTOE hence only around 15 % of the total requirement was metdomestically while the rest was imported, summing up to be staggering USD9440.71 million. From figure # 1.2 nearly 50% of the oil is consumed intransportation sector alone which corresponds to a worth of USD ½ billion. In acountry like Pakistan where per capita income is less than 1100 USD, ½ billion isreally a burden on economy. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 3
    • 1.4 Energy consumption in transportation (international perspective)Energy use in the transportation sector includes the energy consumed in movingpeople and goods by road, rail, air, water, and pipeline. The road transportcomponent includes light-duty vehicles, such as automobiles, sport utility vehicles,minivans, small trucks, and motorbikes, as well as heavy-duty vehicles, such aslarge trucks used for moving freight and buses used for passenger travel.Consequently, transportation sector energy demand hinges on growth rates for botheconomic activity and driving the population. Economic growth spurs increases inindustrial output, which requires the movement of raw materials to manufacturingsites, as well as the movement of manufactured goods to end users.Almost 20 percent of the worlds total delivered energy is used in the transportationsector, where liquid fuels are the dominant source. Transportation alone accountsfor more than 50 percent of world consumption of liquid fuels, and its shareincreases over the projection period. The transportation share of total liquid fuelsconsumption rises to 61 percent in 2035, as their share declines in the other end-use sectors. Because liquids play a key role in the world transportation sector,understanding how the sector is likely to evolve could be the most important factorin assessing the future of liquid fuel markets. From 2007 to 2035, growth intransportation energy use accounts for 87 percent of the total increase in worldliquids consumption. (Source: International Energy Outlook 2010 (Transportation) http://www.eia.doe.gov) Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 4
    • Table#1.1 Overview of U.S. Petroleum Production, Imports, Exports, and Consumption. Source: http://www.bts.gov (Bureau of Transportation Statistics) (R) (R) (R) (R) (R) (R) (R) (P) 1990 1991 1992 1993 1994 1995 1997 1998 1999 2002 2004 2005 1996 2000 2001 2003 2006 2007 2008 2009Domesticproduction, 8.91 9.08 8.87 8.58 8.39 8.32 8.29 8.27 8.01 7.73 7.73 7.67 7.63 7.40 7.23 6.90 6.84 6.85 6.73 7.27totala (R) (R)Crude oilb 7.36 7.42 7.17 6.85 6.66 6.56 6.46 6.45 5.82 5.80 5.75 5.68 5.42 5.18 5.10 5.06 4.95 5.36 6.25 5.88Natural gas 1.56 1.66 1.70 1.74 1.73 1.76 1.83 1.82 1.76 1.85 1.91 1.87 1.88 1.72 1.81 1.72 1.74 1.78 1.78 1.91plant liquidsGross 8.02 7.63 7.89 8.62 9.00 8.83 9.48 10.16 10.71 10.85 11.46 11.87 11.53 12.26 13.15 13.71 13.71 13.47 12.92 11.69imports, totalCrude oilb,c 5.89 5.78 6.08 6.79 7.06 7.23 7.51 8.23 8.71 8.73 9.07 9.33 9.14 9.66 10.09 10.13 10.12 10.03 9.78 9.01Petroleum (R) (R) (R) 2.12 1.80 1.83 1.93 1.97 1.94 2.12 2.39 2.54 2.39 2.60 3.06 3.59 3.59 3.44 3.13 2.68productsd 1.84 1.61 2.00 (R) (R)Exports 0.86 1.00 0.95 1.00 0.94 0.95 0.98 1.00 0.94 1.04 0.97 1.03 1.05 1.16 1.32 1.43 1.80 2.02 0.94 0.98U.S. net (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) 8.50 9.16 9.91 10.42 10.90 11.24 12.39 12.04 11.11 9.67importse 7.16 6.63 6.94 7.62 8.05 7.89 9.76 10.55 12.10 12.55U.S. (R)petroleum 16.99 16.71 17.03 17.24 17.72 17.72 18.31 18.92 19.52 19.70 19.65 19.76 20.03 20.73 20.80 20.69 20.68 19.50 18.77 18.62consumptionBy the (R) (R) (R) (R) (R) (R) (R) (R) (R) (R)transportation 11.12 11.92 12.42 13.01 12.94 13.32 14.18 14.29 13.71 13.27 10.89 10.76 10.88 11.42 11.67 12.10 12.76 13.21 13.72 13.96sectorTransportationpetroleum useas a percent (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) 143.7 155.0 168.3 168.7 180.0 207.3 208.6 203.6 182.6of domestic 122.1 118.6 122.7 129.6 136.1 140.2 146.3 165.1 173.2 189.8 202.4petroleumproductionTransportationpetroleum useas a percent (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) 65.1 65.7 66.0 65.8 66.5 68.5 69.1 70.3 70.7of domestic 64.1 64.4 63.9 64.5 64.4 65.8 65.0 65.4 66.8 66.2 67.1petroleumconsumptionWorld (R) (R) (R) (R) (R) (R) (R) (R) (R)petroleum 66.69 70.13 71.67 73.43 76.74 77.47 79.68 85.20 86.14 85.75 U 67.29 67.48 67.60 68.92 74.07 75.76 78.12 82.46 84.04consumption Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 5
    • Fig # 1.3 Future liquid fuel consumption prediction Source: International Energy Outlook 2010 (Transportation) http://www.eia.doe.govAccording to some researchers the world is left with 40 years of oil and 65 years ofgas if we keep consuming on the same rate as we are right now. In this regard it isour moral and humanitarian obligation to try and find out ways of reducing theconsumption of the precious fuels.1.3 Energy use in transportation and environmental impact Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 6
    • CO2 emissions by sector, Pakistan, 1999 10% 5% electricity & heat production 29% 26% Other energy industries Manufacturing & construction Transportation Residences 29% Other sectors 1% Fig #1.4 CO2 emissions by sector (Pakistan) Source: www.earthtrends.wri.orgTransportation sector in Pakistan is a major contributor towards greenhouse gasemissions. Figure # 1.4 shows CO2 emission by sector in Pakistan for the year1999, which suggests that 26% of the total emissions of CO2 were made bytransportation sector in year 1999. Global warming is a major concern these days,which is caused by greenhouse gases in our atmosphere. Keeping in view theimpact it is having on our life as we know it, latest of which is 2010 Super Flood inPakistan which affected more than 20 million Pakistani’s, greenhouse gasemissions (particularly CO2) if not curtailed may have serious implications.Looking at the economic perspective Pakistan is not self sufficient in Oil and greatdeal of foreign exchange is spent every year to fulfill oil requirement of the nation.Therefore it is very important that Oil consumption in Pakistan be made moreefficient. In order to do so let’s have a look at the largest oil consumer which is Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 7
    • transport sector. Fuel consumption in transport sector can be brought down infollowing possible ways 1. By doing demand side management (DSM) 2. By coming up with new cleaner, cheaper and more environment friendly resources of energy like Solar, Bio-fuel etc. 3. By improving energy efficiency of vehiclesThe proposal made in this thesis deals with the third option which is to improve theenergy efficiency of vehicles. In order to do so first the areas where loses occurhave to be identified. Steps towards improving automobile’s energy efficiency Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 8
    • Overall efficiency of an automotive may increase if the already existing parts of it function more efficiently or some auxiliary efficiency improving systems like turbo chargers are incorporated in to the vehicle. First areas of an automobile where losses occur must be identified, which can be mechanical losses of Engine, Aerodynamic losses, rolling friction, last but definitely not the least automobile Brakes. Figure # 1.5 produced by Eaton hydraulics USA suggests that on average automobile brakes accounts for around 50% of the total losses that occur in an urban vehicle. Hence making it the largest share holder of the total energy lost. Energy lost due to brake can be recovered by using considerably new phenomenon of Regenerative braking. As the name suggests in such brake mechanisms energy lost in conventional brake due to friction is converted to some form that can be reused again. Two types of regenerative braking systems for vehicles are known; 1. Electrical regenerative brake 2. Hydraulic regenerative brake Electrical regenerative braking system uses excess energy to power a reversible generator and charges a battery to for future use, while Hydraulic regenerative braking system stores access energy in hydraulic form to reuse. Drawback of electric regenerative braking is that it can only be used in Electric or ElectricTable#2.1 Hybrid vehicles which in urban very commonly used around Pakistan. On the energy loss due to brake are not contrary Hydraulic regenerative braking system can be employed on any conventional I.C engine powered vehicle hence can have wider impact on the overall energy situation. Hydraulic Regenerative Braking is an obvious choice between the two. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 9
    • Design and modeling of Hydraulic Regenerative Braking System for Vehicles | Fig # 1.5 Urban Vehicle energy loss in Braking, Aerodynamic and Rolling friction Source: http://www.eaton.com/EatonCom/ProductsServices/Hybrid/SystemsOverview/HydraulicHLA/10
    • 1.4 Maximum available potentialTo appreciate potential available for Hydraulic Regenerative Braking system let’shave a sample calculation that can give us an idea of how much energy is availablefor regeneration.Calculations below have been made neglecting the aerodynamic and rollingfriction losses. It is assumed that the vehicle’s engine runs at maximum efficiency.Considerations: Fully loaded medium sized Diesel truck weighing 25 tons, runningat 30 km/hr. It is an urban service truck which is supposed to cover a distance of 10km, with expected stop at every 200 m due to traffic and service compulsions. Thetime duration between pressing the brake paddle and vehicle coming to halt is 4sec. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 11
    • Following example demonstrates the amount of energy lost in conventionalautomobile brake. If recovered part of it can bring improvement in energyefficiency in transportation.  Truck Mass (m) = 25 tons = 25000 kg  Initial speed (vi) = 30 km/hr = 8.333 m/sec  Final speed (vf) = 0 m/s  Average mileage = 5 km/L  Distance traveled = 10 km  Total fuel consumption = Distance traveled / Average mileage = 10/5 = 2 L  Density of diesel = 0.832 kg/L  Average C.Vdiesel = 36 MJ/L = 43.27 MJ/kg  Distance / Stop = 200m  Number of stops = 50  Time taken to reach zero velocity (t) = 4 secEnergy required to stop vehicle W = F.d ------------ (i) F = m.a ------------- (ii) a = vf – vi ---------- (iii) t d = distance traveled after pressing brake paddle Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 12
    • d = vi t + ½ a t2 --- (iv) by putting the values of speed and time in eq: (iii) and (iv) a = 2.0833 m/s2 d = 16.666 m put a = 2.0833 m/s2 in eq: (ii)∴ F = 52082.5 N = 52.08 kN put value of ‘F’ and ‘d’ in eq: (i)∴ W = 868041.3 J = 868.04 kJ = 0.868 MJ/stopHence energy lost in 50 stops = 0.868 x 50 This energy loss corresponds to diesel = 43.4 MJ consumption of 2 L = 1.664 kg.Comparison with total energy consumed Fuel consumption = Distance traveled / Average mileage = 10 / 5 = 2 L Total energy consumed = Fuel consumption x Average C.Vdiesel = 2 x 36 = 72 MJ Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 13
    • % energy loss due to braking = Energy lost in braking x 100 Total energy consumed = (43.4 / 72) x 100 = 60.3 %In light of above calculation it is evident that automobile brake is a huge source ofenergy loss and if recovered it can contribute a great deal towards improvingenergy efficiency of automobile. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 14
    • Chapter 2Hydraulic Regenerative Brakingsystem2.1 ComponentsHRB (Hydraulic Regenerative Braking) system consists of following maincomponents 1. Transfer case 2. Hydraulic machine (Pump/Motor) 3. Accumulator 4. Low pressure reservoir 5. Power transmission fluid 6. Controller Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 15
    • Transfer caseTransfer case is a gearbox which brings power from main propeller shaft to thehydraulic machine. It is similar to the PTO (Power Take Off) used in agriculturalmachinery.Transfer case can be of two kinds • Constant mesh gear box • Variable transmission gear boxConstant mesh gearboxSuch transfer case has only two gears that always remain meshed with each other.It brings power from main shaft to the reversible pump and then back. Advantages LimitationEasier to design, since only two gears Limited speed range.have to be designed.Less complex manufacturing and repair. Bigger in size.Easier design of controller Not good manipulator of available power.Variable transmission gearbox Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 16
    • A gearbox having more than single mesh arrangement, in which gear can bechanged as the speed of vehicle increases is called variable transmission gearbox.There can be two or more than two pairs of gear mounted on each shaft, which willeach engage as the vehicle approaches their operating speed.Such systems enable better distribution of the energy available and tend to increasethe speed range in which the apparatus can be used. Advantages LimitationGreater speed range. Complex design.More energy efficient. Sophisticated controller required.Smaller in size. Complex manufacture and repair. Hydraulic Machine Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 17
    • Here the requirement from the Hydraulic machine is to work both as a pump andhydraulic motor. In first stage of operation the machine has to act as a pump and inlater as a motor. This constraint leaves us with only a few options that are • Gear pump/motor • Swash plate pump/motor • Bent axis pump/motorGear pump/motorA gear pump uses the meshing of gears to pump fluid by displacement. They areone of the most common types of pumps for hydraulic fluid power applications.Gear pumps are also widely used in chemical installations to pump fluid with acertain viscosity. There are two main variations; external gear pumps which usetwo external spur gears and internal gear pumps which use an external and aninternal spur gear. Gear pumps are positive displacement (or fixed displacement),meaning they pump a constant amount of fluid for each revolution. Some gearpumps are designed to function as either a motor or a pump. WorkingAs the gears rotate they separate on the intake side of the pump, creating a voidand suction which is filled by fluid. The fluid is carried by the gears to thedischarge side of the pump, where the meshing of the gears displaces the fluid. Themechanical clearances are small— in the order of 10 μm. The tight clearances,along with the speed of rotation, effectively prevent the fluid from leakingbackwards. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 18
    • The rigid design of the gears and houses allow for very high pressures and theability to pump highly viscous fluids. Fig#2.1 Exploded view of gear pump Source: www.wikipedia.orgSwash plate pump/motor Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 19
    • An axial piston / swash plate pump is a positive displacement pump that has anumber of pistons in a circular array within a cylinder block (Chamber). It can beused as a stand-alone pump, a hydraulic motor or an automotive airconditioning compressor. Components of swash plate pump/motor • Housing • Plungers • Chamber • Swash plate • Valve plate Chamber Plungers Swash plate Housing Fig#2.2 Swash plate pump Source: AuthorFeatures Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 20
    •  Swash plate serves as a cam for the plungers as the plungers move along the plate they raise as the plate rises and go for suction as the plate goes down. Angle of swash plate determines the compression ratio of the pump it can be increased by increasing the angle of swash plate hence increasing the displacement of the plungers. The angle of swash plate is controlled using feedback from high pressure and low pressure reservoirs.  Normally there are odd number of pistons most common arrangement is 9 pistons.  These pumps are used where space is confined and the output has to be given in the axial direction.  According to Eaton Hydraulics USA recommended viscosity range of fluids for such pumps is 16 – 40 cSt.Bent axis pump/motorWorking of bent axis motors is same as that of swash plate motors only because ofthe bent casing the swash plate cannot change its inclination to compensatevariable pressure requirements. Accumulator Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 21
    • A hydraulic accumulator is an industrial device basically used for storage ofenergy. In this device, a non-compressible hydraulic fluid is held under pressurefor an outside source. This external or outside source can be compressed gas orspring or raised height. Considered as pressure storage device, a hydraulicaccumulator is used to store hydraulic energy.Compressed gas accumulators are by far the most common type. These are alsocalled hydro-pneumatic accumulators.Types of accumulatorRaised weight accumulatorA raised weight accumulator consists of a vertical cylinder containing fluidconnected to the hydraulic line. The cylinder is closed by a piston on which aseries of weights are placed that exerts a downward force on the piston and therebyenergizes the fluid in the cylinder. In contrast to compressed gas and springaccumulators, this type delivers a nearly constant pressure, regardless of thevolume of fluid in the cylinder, until it is empty. (The pressure will declinesomewhat as the cylinder is emptied due to the decline in weight of the remainingfluid.)Compressed gas (or gas-charged) accumulatorA compressed gas accumulator consists of a cylinder with two chambers that areseparated by an elastic diaphragm, a totally enclosed bladder, or a floating piston.One chamber contains hydraulic fluid and is connected to the hydraulic line. Theother chamber contains an inert gas under pressure (typically nitrogen) that Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 22
    • provides the compressive force on the hydraulic fluid. Inert gas is used becauseoxygen and oil can form an explosive mixture when combined under high pressure.As the volume of the compressed gas changes the pressure of the gas, and thepressure on the fluid, changes inversely.The compressed gas accumulator was invented by Jean Mercier, for use in variablepitch propellers.Spring typeA spring type accumulator is similar in operation to the gas-charged accumulatorabove, except that a heavy spring (or springs) is used to provide the compressiveforce. According to Hookes law the magnitude of the force exerted by a spring islinearly proportional to its extension. Therefore as the spring compresses, the forceit exerts on the fluid is increased linearly.Metal bellows typeThe metal bellows accumulators function similarly to the compressed gas type,except the elastic diaphragm or floating piston is replaced by a hermetically sealedwelded metal bellows. Fluid may be internal or external to the bellows. Theadvantages to the metal bellows type include exceptionally low spring rate,allowing the gas charge to do all the work with little change in pressure from fullto empty, and a long stroke relative to solid (empty) height, which gives maximumstorage volume for a given container size. The welded metal bellows accumulatorprovides an exceptionally high level of accumulator performance, and can beproduced with a broad spectrum of alloys resulting in a broad range of fluidcompatibility. Another advantage to this type is that it does not face issues withhigh pressure operation, thus allowing more energy storage capacity. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 23
    • Spring-loaded pistonA spring-loaded piston accumulator is identical to a gas-charged unit, except that aspring forces the piston against the liquid. Its main advantage is that there is no gasto leak. A main disadvantage is that this design is not good for high pressure andlarge volume. Fig#2.3 Working mechanism of different types of accumulators Source: www.google.com.pk Low pressure reservoir Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 24
    • Low pressure reservoir is a storage tank that holds hydraulic fluid at low pressure.It should be made of material that is chemically inert to the hydraulic fluid, so thatthe power transmission fluid does not get contaminated. Fig# 2.4. Oil tank with strainer on top Source: www.google.com.pk Controller Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 25
    • An efficient controller can dramatically improve the performance of the system.Controller can either be PLC (Programmable Logic Controller) based or microcontroller based.Job of controller is mainly to engage or disengage clutch. Since speed range for thesystem is limited therefore the controller must be able to decide whether to engagethe clutch or not. In case of variable transmission transfer case controller has toperform an additional task of switching gears as the speed changes.Following are the parameters that should be considered before choice or design ofcontroller. • Controller must be rigid enough to sustain environmental conditions. • Controller must be temperature resistant • Controller must be water proof • Controller must be shock resistant Power transmission fluidsHydraulic fluids, also called hydraulic liquids, are the medium by which power istransferred in hydraulic machinery. Common hydraulic fluids are based on mineral Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 26
    • oil or water. Examples of equipment that might use hydraulic fluidsinclude excavators and backhoes, brakes, power.Steering systems, transmissions, garbage trucks, aircraft flight controlsystems, elevators, and industrial machinery.Hydraulic systems like the ones mentioned above will work most efficiently if thehydraulic fluid used has low compressibility.Brake fluid is a type of hydraulic fluid used in hydraulic brake applicationsin automobiles, motorcycles, light trucks, and some advanced bicycles. It is used totransfer force into pressure. It works because liquids are notappreciably compressible - in their natural state the component molecules do nothave internal voids and the molecules pack together well, so bulk forces aredirectly transferred to trying to compress the fluids chemical bonds. Brake fluidsmust meet certain requirements as defined by various standards set byorganizations such as the SAE, or local government equivalents. For example,most brake fluid sold in North America is classified by the US Department ofTransportation (DOT) under their own ratings such as "DOT 3" and "DOT 4".Their classifications broadly reflect the concerns addressed by the SAEsspecifications, but with local detailsService and maintenanceMost automotive professionals agree that glycol-based brake fluid; (DOT 3, DOT4 and DOT 5.1) should be flushed, or changed, every 1–2 years. Manymanufacturers also require periodic fluid changes to ensure reliability and safety.Once installed, moisture diffuses into the fluid through brake hoses and rubberseals and, eventually, the fluid will have to be replaced when the water contentbecomes too high. Electronic testers and test strips are commercially available to Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 27
    • measure moisture content. The corrosion inhibitors also degrade over time. Newfluid should always be stored in a sealed container to avoid moisture intrusion.ExamplesDOT 3 Polyethylene glycol-basedDOT 4 Polyethylene glycol-basedDOT 5 Silicone based Oil Dry boiling point Wet boiling point DOT 3 205 °C (401 °F) 140 °C (284 °F) DOT 4 230 °C (446 °F) 155 °C (311 °F) DOT 5 260 °C (500 °F) 180 °C (356 °F) DOT 5.1 270 °C (518 °F) 190 °C (374 °F)2.2 Working mechanism Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 28
    • Fig # 2.5 Hydraulic Regenerative Braking (Schematic View) Source: AuthorThe working of the proposed system may be broadly divided into two stages 1. Regeneration mode:When it is intended to stop the vehicle, driver applies brake. During application ofbrake power produced by engine and inertia of vehicle are of no use anymore.Pump is engaged and operates by this energy and pumps hydraulic fluid from lowpressure tank to the high pressure accumulator. The energy is stored inaccumulator which is also called mechanical charger and can be reused wheneverneeded. 2. Launch assist mode:When vehicle needs to be accelerated, driver presses the accelerator. In suchsituation rather than using engine power oil in accumulator is used to drive thehydraulic machine that now will work as a motor, which in turn makes the vehiclemove. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 29
    • Fig#2.6 Schematic view Hydraulic Regenerative Braking Source: www.eaton.com2.3 Areas of applicationDesign and modeling of Hydraulic Regenerative Braking System for Vehicles | 30
    • Hydraulic regenerative braking can be highly effective for urban vehicles. It is bestsuited for vehicles with short stop and go cycles examples are; • School buses • Public transport buses • Refuse trucks that collect garbage • Delivery vans etcAccording to “The Nation” newspaper“The number of registered vehicles in the Federal Capital has crossed the figureof 0.3 million as the vehicles of embassies were not included in this figure.” (Feb: 24, 2009) Total area of Islamabad is 233 km2∴ Vehicle density in Islamabad ≈ 1300 vehicles / km2At such high vehicle density, traffic jams and unexpected stoppages are nosurprise. Such environments are ideal for systems like Hydraulic RegenerativeBraking. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 31
    • 2.4 Parallel developmentsHydraulic regenerative braking system is a fairly new idea in energy efficiencyimprovement in transportation sector. Many mainstream companies both inautomobile and hydraulics are working on design and development of HydraulicRegenerative Braking systems, some designs as proposed by different internationalcompanies are mentioned; 1 Hydrostatic Regenerative Braking (Bosch Rexroth) Fig # 2.7 Hydrostatic Regenerative Braking Source: www.bosch Rexroth.com 2 Hydraulic Launch Assist (Eaton Hydraulics) Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 32
    • Fig # 2.8 Hydraulic Launch Assist Source: www.eaton.com 3 Runwise (Parker) Fig # 2.9 Parker’s Runwise Source: www.parker.comDesign and modeling of Hydraulic Regenerative Braking System for Vehicles | 33
    • Chapter 3Types of HRBHydraulic regenerative braking system can be classified on two grounds 1. On the basis of Hydraulic machine  HRB with reciprocating type hydraulic machine  HRB with Swash plate type hydraulic machine 2. On the basis of Transfer case  HRB with constant gear ratio transfer case  HRB with variable transmission transfer case Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 34
    • Hydraulic regenerative Braking system with3.1 reciprocating type hydraulic machine Fig# 3.1 Components of HRB Source: AuthorVehicle weight actuated generator gave rise to the idea of a similar mechanismmounted on the vehicle chassis, which uses brake energy rather than vehicleweight, hence makes it much lighter.It is a mechanical charger unit that charges on the energy otherwise wasted due tobraking and allows the reuse of the stored energy.A reciprocating type unit is used to serve as reversible pump. 1. Transfer case: 2. Clutch: 3. Pump/Motor unit: 4. Accumulator: Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 35
    • Drawbacks • Reciprocating unit not generally used as hydraulic motor • More fluid intake volume per revolution • Vibration • Bulky design3.2 Hydraulic Regenerative Braking System with constant gear ratio Transfer caseDesign and modeling of Hydraulic Regenerative Braking System for Vehicles | 36
    • Fig# 3.2 Constant gear ratio transfer case with swash plate unit and clutch Source: AuthorThis design is for low speed application because of the limitation of the gears.Because only one gear arrangement is given and the pump has a maximum limit ofspeed it can work on hence this system can only work in a given range of speed.Both pinion and gear are of same size.3.3 Hydraulic Regenerative Braking system with variable transmission transfer case Fig# 4.5 helical gear Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 37
    • Fig# 3.3 Variable transmission transfer case with swash plate unit and clutch Source: AuthorThis system can work with a wider speed range because of the variabletransmission transfer case provided that can keep the pump under safe operatingspeed. Only problem is the complex design of its transfer case.Chapter 4Modeling and AnalysisThe design is proposed for a medium size truck (capacity 15 – 30 Ton) withfollowing specifications. All the 3d models and simulations have been done usingSolidedge V19 licensed to Mehran University of Engineering and Technology.Empty weight 10 TonLoaded weight 15 TonGross weight 25 Ton Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 38
    • Maximum rated power 220 hp = 160 kW Maximum propeller shaft speed 3000 r.p.m Hydraulic Regenerative Braking system with Variable Transmission Transfer case Transfer Fig# 4.1 Volvo F10 Pump / case Source: www.3dcontentcentral.com Motor UnitAccumulator Low Pressure Reservoir Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 39 Fig # 4.2 Hydraulic Regenerative Braking system with variable transmission transfer case Source: Author
    • Fig # 4.3 Hydraulic Regenerative Braking system (showing gear meshing) Source: AuthorDesign and modeling of Hydraulic Regenerative Braking System for Vehicles | 40
    • 4.1 Transfer case Gear # 3 Gear # 4 Gear # 2 Gear # 1 Fig # 4.4 Transfer case and axial piston unit (Exploded View)Table # 4.1 Source: specifications of gear # 1 and 2 Design Author Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 41
    • Gear # 1 and 2 < 2000 r.p.m Material Carbon steel (CS 125) Diameter (both gears) 150 mm Gear ratio 1 Face width 32 mm Helix angle 0o Max: speed 3000 rpm Max: power 160 kW No: of teeth 28Table # 4.2 Design specifications of gear # 3 and 4 Gear # 3 and 4 > 2000 r.p.m Material Carbon steel (CS 125) Diameter (gear # 3) 100 mm Diameter (gear # 4) 200 mm Gear ratio 2 Face width 40 mm Helix angle 0o Max: speed (gear #3) 3000 rpm Max: power 160 kW No: of teeth (gear # 3) 17 No: of teeth (gear #4) 34 Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 42
    • The results shown above have been generated and verified using “Spur geardesigner” module of “Solid edge V19”, which uses NASTRAN solver to verifyresults.Gear #1 and 2 will remain engaged at propeller shaft speeds less than 2000r.p.m,while gear # 3 and 4 will engage speed greater than 2000 r.p.m. Speed range foreach gear arrangement has been selected considering the fact that the assumedpump/ motor unit has maximum working speed of 2000 r.p.m, therefore in nocircumstances the speed of pump shaft shall exceed 2000 r.p.m. Fig # 4.5 Variable transmission transfer case Source: Author Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 43
    • 4.2 Accumulator Fig # 4.6 Solid Edge V19 (Spur Gear designer module) Source: AuthorDesign and modeling of Hydraulic Regenerative Braking System for Vehicles | 44
    • Gas charged bellow type accumulator is used because of ease of availability andmaintenance. These accumulators almost never fail or need maintenance in theirstandardized lifetime.Usable volume 15 L = 15000 cm3Maximum pressure 210 bar Fig # 4.7 Hydraulic Accumulator Source: Author4.3 Pump / Motor unit Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 45
    • Swash plate pump / motor is best suited for the application because of its compactsize and precedence of application in hydraulic power transmission.SpecificationsNo: of plungers 9Plunger dia: 2 cmChamber dia: 10 cmSwash plate angle 250Maximum speed 2000r.p.mVolume flow / revolution = Cross section area of each plunger x total displacement x No: of plungers = (pie /4 x 22) x 3.73 x 9 = 105.4 cm3/ rev:Time to fill the accumulator =Volume of accumulator / (Volume flow rate / rev: x maximum allowable speed) = 15000 / (105.4 x 2000/60) = 4.3 sec Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 46
    • Fig # 4.8 Swash plate pump/motor assembly Source: AuthorDesign and modeling of Hydraulic Regenerative Braking System for Vehicles | 47
    • Fig #4.9 Swash Plate pump / motor dimensions (mm) Source: Author4.4 Sample calculation with HRBData considered here is from article # 1.4 (Maximum available potential). Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 48
    • HRB specifications  Accumulator volume = 15 L  Accumulator pressure = 210 bar = 210 x105 N/m2  Time required to fill Accumulator = 4 sec  No: of pistons in Axial piston unit = 9  Volume flow rate of Axial piston unit = 105.4 cm3 / rev:  Maximum speed of Axial piston unit = 2000 r.p.mEnergy accumulated by HRB / stop = Accumulator pressure x Accumulator volume = 210 x 105 x 15/1000 = 315000 J = 0.35 MJTotal energy accumulated = Energy accumulated / stop x No: of stops = 0.35 x 50 = 17.5 MJTotal energy lost due to braking = 43.4 MJ (from article # 1.4) With HRB in place 40 % of the energy% Energy recovered with HRB = Total energy accumulated x100 that previously was Total energy lost due to braking wasted can be recovered and put to = (17.5/43.4) x 100 = 40.3 % positive use.% Increase in mileageTotal available energy = Fuel consumption x Average C.VDiesel = 2 x 36 = 72 MJ/L Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 49
    • Total energy lost in braking = 43.4 MJNet energy available for accelerating (without HRB) = 72 – 43.4 = 28.6 MJEnergy recovered with HRB = 17.5 MJNet energy available for accelerating (with HRB) = 28.6 + 17.5 = 46.1 MJWhich is enough for the vehicle to travel 16 km as compared to 10 km withoutHRB.Result: 60% increase in mileage∴ New mileage = 16/2 = 8 km/L% increase in mileage = (7-5 /5) x 100 = 40 %% cost savingMileage with HRB = 8 km/LMileage without HRB = 5 km/L% cost saving = (1 – mileage without HRB/mileage with HRB) x 100 Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 50
    • = (1 – 5/8) x 100 = 37.5 %Money saved in fuel by installing HRB in given setup can be as high as 37.5 %. Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 51
    • Fig #4.10 Hydraulic Regenerative Braking System assembly in Truck Source: AuthorDesign and modeling of Hydraulic Regenerative Braking System for Vehicles | 52
    • Fig # 4.11 Hydraulic Regenerative Braking system in Truck (orthogonal projection) Source: Author4.5 Fabricated modelDesign and modeling of Hydraulic Regenerative Braking System for Vehicles | 53
    • To demonstrate the working of HRB a model has been fabricated with resourcesgenerated locally. Following are the specificationsAxial piston unitNo: of pistons 9Volume flow rate/rev 0.278 in3/revMaximum speed 2000 r.p.mMaximum volume flow rate 556 in3/min = 9.26667 in3/secMaximum pressure 210 bar (3000 psi)Direction of rotation Counter clockwiseAccumulatorType Bladder typePowered by Nitrogen gasVolume 0.5 LMaximum pressure 210 bar Overall cost Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 54
    • Axial piston unit (Used) Rs. 8000Accumulator (Used) Rs. 6000Gears, Bearings, Shafts, Mounting Rs. 14000plate, Valve, Pipes and Servicecharges.Miscellaneous Rs.3000Total cost Rs. 31000Chapter 5Cost estimate of full scaleprototype Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 55
    • Full scale prototype ready for testing for the proposed design can cost up to Rs.200,000.Swash Plate pump/ motor $ 400 to $ 1500 (www.ebay.com)Accumulator $ 1090 (www.alibaba.com)Transfer case $ 500 approxController $ 200 approxMountings and accessories $ 200 approxMinimum total cost $ 2400 ≈ Rs. 200,0005.1 Payback period Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 56
    • Payback period refers to the period of time required for the return on an investmentor to "repay" the sum of the original investment.Considering today’s price of Diesel (Green XL of PSO) Rs. 78.33 per liter.Total investment on HRB Rs. 200,000Daily running of vehicle 50 kmAnnual running of vehicle 50 x 300 = 15000 kmPayback period = Total investment/ Annual fuel cost savingAnnual fuel saving = Saving (L/km) x Annual running of vehicle = (0.75/10) x 15000 = 1125 LAnnual fuel cost saving = 1125 x 78.33 = Rs. 88121.25Payback period = 200,000 / 88121.25 = 2.3 years = 2 years 4 monthsInitial investment can be recovered in a period of 2years and 4 months. Service lifeof vehicles is way longer then the payback period, therefore this figure is attractive.Result discussion and conclusion Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 57
    •  Energy lost due to conventional friction braking of automobile is very high.  HRB offers a great improvement in energy efficiency and reduction in emission of greenhouse gases.  Payback period is as low as 2 years and 4 months for a vehicle doing only 50 km a day.  In specific case 60 % increase in mileage.  37.5 % less spending on fuel.  System is feasible for  Urban mass transit buses  Refuse trucks  Construction site vehicles  Cars  Considering Pakistan’s case 37.5 % saving in fuel consumption means as high as USD 0.1875 billion = USD 187.5 million ≈ Rs. 16 billion In fiscal year 2010-11 money allocated for health sector in the province of Sindh, Pakistan is Rs. 16.9 billion. Comparing to that Rs. 16 billion can almost double the health budget in province of Sindh, Pakistan.  Systems like HRB are the need of the age where environmental problem is ever increasing and fossil fuel reserves depleting at a rate faster than ever before. Therefore such eco friendly systems should be promoted and governments around the world should allocate funds for research andDesign and modeling of Hydraulic Regenerative Braking System for Vehicles | 58
    • development of such systems for the betterment of human life and its survival on earth.ReferencesBooks and literature Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 59
    • 1 A textbook of Machine design by R.S Khurmi and J.K Gupta 2 The Nation Daily Feb 25th 2009 3 Pakistan energy year book 2009 Issued by Hydrocarbon Development Institute, Ministry of Petroleum and Natural Resources, PakistanSoftware 4. Solidedge V19 5. Microsoft Paint 6. Microsoft OfficeInternet 7. www.google.com.pk 8. www.wikipedia.org 9. www.eaton.com Eaton Hydraulics 10. www.boschrexroth.com Bosch Rexroth 11. www.parker.com Parker Hannifin Corporation 12. www.eia.doe.gov Energy Information Administration (USA) 13. www.bts.gov Bureau of Transportation Statistics (USA) 14. www.3dcontentcentral.com Solidworks community 15. www.aesti.com Alternate Energy Source Technology Inc. 16. www.ebay.com 17. www.alibaba.com 18. www.earthtrends.wri.org Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 60