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GrittTopics To Be Presented: 3 Topics To Be Presented The Basic Concepts Hydraulic layouts Component functions Brake Balance Stopping Distance and Fade Formula SAE vs. Mini Baja Lessons Learned The Rules QuestionsThe Basic Concepts: 4 The Basic Concepts Kinetic energy = heat F = ma Newton is always right! Do the calculations first When all else fails see rule 3.Energy Conversion: 5 Energy Conversion The brake system converts the kinetic energy of vehicle motion into heatEnergy Conversion: 6 Energy Conversion A vehicle weighing 290 kg. (639 lbs.) At 90 kph (55.9 mph) has kinetic energy of: Stopping the vehicle at .9G takes 2.9 Seconds This is equal to 31 kilowatts (42 HP). OR 90 ,770 N-M.PowerPoint Presentation: 7PowerPoint Presentation: 8 F = ma The Key Question! How do you calculate F?PowerPoint Presentation: 9 Basic System Model Brake ForceHydraulic System Configurations: 10 Hydraulic System Configurations There are two layouts of hydraulic brake systems used in cars and light trucks. Front/Rear hydraulic split: Also called axle by axle, vertical, and some times “black and white”. Diagonal Split: Also called criss-cross. The type of split is only significant in the event of a hydraulic system failure.Front/rear Hydraulic Split: 11 Front/rear Hydraulic Split Front Axle Rear Axle Primary System Secondary SystemPowerPoint Presentation: 12 Diagonal Split System In a diagonal split system, one brake line is run to each rear brake and one to each front brake. The connections are such that the left front and the right rear brake are on one circuit and the right front and left rear are on the other circuitTypical Diagonal Split System: 13 Typical Diagonal Split SystemPowerPoint Presentation: 14 Brake Component FunctionFour Sub-systems: 15 Four Sub-systems Actuation sub-system Foundation sub-system Parking brake sub-system ABS & ESP ( electronic stability program) sub-systemActuation Sub-system: 16 Actuation Sub-system Brake Pedal Master Cylinder Proportioning Valves Brake Lines 16The Brake Pedal: 17 The Brake Pedal Driver Input Output to master cylinder 100 N and 144 mm 400 N and 36 mm 4:1 Nominal Pedal RatioMaster Cylinders: 18 Master Cylinders Output Pressure Input Force A master cylinder is just a simple piston inside a cylinderM/C Unapplied: 19 M/C UnappliedM/C Applied: 20 M/C AppliedPrimary System Failure: 21 Primary System Failure Operated Mechanically Bottoms Against Secondary Piston Pressure for Normal Secondary System FunctionSecondary System Failure: 22 Secondary System Failure Bottoms at End of Cylinder Bore Pressure for Normal Primary System FunctionProportioning Valves: 23 Proportioning Valves Split Point Slope Hard Stops Reduce the pressure to the rear brakes Diagonal systems require two Split and slope are changed to create proper balanceAdjustable Proportioning valves: 24 Adjustable Proportioning valves Wilwood Tilton Only the split points are adjustablePowerPoint Presentation: 25 Brake Lines Double wall steel tubing (Bundy Tubing) is industry standard. 3/16” o.d. is standard size. Very robust, can take a lot of abuse Use SAE 45° inverted flare (J533 and J512) joints if you can.Foundation Brake Sub-system : 26 Foundation Brake Sub-system Disc Brakes LiningsFront Disc Brake: 27 Front Disc BrakeFront Disc Brake: 28 Front Disc BrakeBrake Linings: 29 Brake Linings Brake linings are probably the most mis-understood part of a brake system. The output of any brake is directly related to the coefficient of friction (µ) between the lining and the disc or drum. The challenge is knowing what the instantaneous value of µ is during any given stop. Any design calculations you do, go right out the window if the lining you use does not have the µ value you assumed.Brake Linings: 30 Brake Linings Remember the equation for a disc brake The best method for determining the actual value of µ for a given lining is from a dynamometer test.Brake Balance: 31 Brake BalanceBoth Front Wheels Locked:: 32 Both Front Wheels Locked: Not good if you are on a curved road You can’t steer OK, if you must hit something The vehicle goes straightBoth Rear Wheels Locked:: 33 Both Rear Wheels Locked: The front wheels track straight ahead Then the rear wheels deviate to the side Until the vehicle can’t track straight any longer and the rear starts to spin around the frontPowerPoint Presentation: 34 µ vs. % Wheel Slip 0 10 20 30 40 50 60 70 80 90 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 % Wheel Slip Mu (Deceleration) Typical Dry Surface Steering BrakingFront Lock: 35 Front Lock If there is more front brake torque than dynamic front weight The front wheels will lock up before the rears 20% 80% 40% 60% Brake torque distribution Dynamic weight distributionRear Lock: 36 Rear Lock If there is more rear brake torque than dynamic rear weight; The rear wheels will lock up before the fronts 40% 60% 20% 80% Brake torque distribution Dynamic weight distributionOptimum Braking: 37 Optimum Braking Optimum braking is achieved when brake torque distribution matches dynamic weight distribution Weight Distribution No Braking Hard Braking 40% 60% 20% 80%Calculating Dynamic Weight Transfer: 38 Calculating Dynamic Weight TransferIdeal Vs Actual Torque: 39 Ideal Vs Actual Torque 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Front Torque Rear Torque Ideal 60/40 Actual 70/30 Actual With a prop valveStopping Distance: 40 Stopping Distance Does not Depend on: Type of brakes Size of brakes Does Depend on: Tire to road friction Vehicle balance Skill of driver System Reaction TimePowerPoint Presentation: 41 µ vs. % Wheel Slip 0 10 20 30 40 50 60 70 80 90 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 % Wheel Slip Mu (Deceleration) Typical Dry Surface BrakingBrake Fade: 42 Brake Fade Brake fade is the loss of performance resulting from the lining friction decreasing as the lining and rotor or drum rises in temperatureFormula SAE vs. Mini Baja: 43 Formula SAE vs. Mini Baja The brake system design must match the vehicle objectivesPowerPoint Presentation: 44 Formula SAE Absolute reliability High Speeds Maximum possible decel without locking Consistent balance with changing temperatures Mini Baja Absolute reliability Low Speeds Very hostile environment Brake must work when wet and muddyPowerPoint Presentation: 45 Mini Baja, Hostile Environment Will your master cylinder fill up with water? How does you brake lining work when it is wet?Lessons Learned : 46 Lessons LearnedDon’t Do Something Because:: 47 Don’t Do Something Because: The other guys do it. All the race cars have it. It looks really coolDesign to a Specific Objective:: 48 Design to a Specific Objective: Do the math first Verify your assumptions Take the easy solution (KISS)PowerPoint Presentation: 49 Lessons Learned Lesson Number 1 - Keep it SIMPLEPowerPoint Presentation: 50 Lessons Learned Lesson Number 2 - Keep it light; but not too light. 90% of the braking energy goes into the rotor If the rotor is too light it gets very hot If the temperatures get too high very nasty things can happen.PowerPoint Presentation: 51 Too light 2006 DCAE program involved a Hemi powered Grand Cherokee. One team used much smaller rear brakes and rotors to save a few pounds on a 3200 lb vehicle with 500 hp. The vehicle went off the end of the main straight at over 100 mph on the third lap because of brake failure.PowerPoint Presentation: 52PowerPoint Presentation: 53PowerPoint Presentation: 54 Lessons Learned Lesson Number 3 - Packaging and Integration drive 90% of design Lesson Number 4 - Read the rules Lesson Number 5 - Allow enough time for details and testingPowerPoint Presentation: 55 Brake rules The car must have four wheel brakes operated by a single control. It must have two independent hydraulic circuits with independent fluid reserves. The brake system must be capable of locking all four (4) wheels, and stopping the vehicle in a straight line The braking systems must be protected with scatter shields from failure of the drive train (FSAE only) A brake pedal over-travel switch must be installed. This switch must kill the ignition and cut the power to any electrical fuel pumps. (FSAE only) The car must be equipped with a red brake light that illuminates when ever the brakes are appliedAny Questions: 56 Any Questions You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.