carello_chassis_1_2015

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Massimiliana Carelloi M i ili C llMechanical and Aerospace Engineering Department e‐mail: massimiliana.carello@polito.itAutomotive Engineering 2014/2015Part Brake Systems1–systems have the following tasks:vehiclethe vehicle speedto keep a halted vehicle stationary2equipment’s functions can be divided system BBA(or footbrake)system HBA(or auxiliary)system FBA(or handbrake)(h db k)system allows to reduce,directlyduring normal driving or todevice.It supplies,regulates and,if necessary, braking.It terminates at the point where energy source is that part of an energymay be located remotely(compressedforce of the driver.control signal can be conveyed withinhydraulic or electrical means,includingforce.The control force is directly applied:force by the driver by hand or foot;driver or without any action(only pressure in a connection line,or the electricenergy brake systemspassenger cars and two‐wheeled vehicles.Thepedal or hand lever is transmitted to the brakesBowden cable)or hydraulic(master cylinder,wheelassisted or energy assisted brake systemspassengers cars and light commercial vehicles.Itunit)to supplement muscular force with energyhydraulic pressureor non‐muscular energy systemsII variant(a)Separate circuit for the front and rear axlesX variant(b)Diagonal circuit patternHI variant(c)One circuit for the front and a second forfront and rear wheels6Motor vehicle must be equipped with two separate brake system,one of which must be lockable.The brake system must have separate control devices.In the event of a fault in the service brake system,it must still be possible for at least two wheels(not at the same side)to be braked.Brake systems in motor vehicles consist of the following assemblies,which offer in B k t i t hi l i t f th f ll i bli hi h ff i design depending on whether the system is hydraulic or pneumatic:‐energy supply,‐control devices,‐transmission devices,‐control facilities,‐wheel brakes,8Brake‐pressureregulating valves Front direction910brake booster is an enhanced master cylinder setup usedthe amount of pedal pressure needed for braking.employs a booster set up to act with the master cylinder hydraulic pressure to the brakes and/or lower force applied pedalbrake pedal.brake booster usually uses vacuum from the engine intakethe force applied by the pedal to the master cylinder,an extra vacuum pump to enable it.the engine running the brakeineffective on the braking capability.braking process is initiated and controlled through the master cylinder.For the car where it is mandatory two separate brake circuits is used a master cylinder designed as a tandem unit.12force applied to the brake pedal act directly on the push‐rod piston(14),whichmoving on the left.As it does so,it passes over the snifter bore(12)and the fluid pressure chamber(21)can press the float piston(6)to the left as well.valve pin(18)is no longer up against the slotted spring pin(7)as soon as thehas moved about1mm to the left.The valve seal(16)presses against the float (6)to seal and insulate the pressure chamber(3)from the intermediate chamber(8).The pressure in both chamber(3and21)will now increase in response to any additional force at the pedal.At the same time both pistons(6and14)will react to decreasing foot pressure by shifting to the right until the snifter bore(12)is exposed or until the valve pin (18)contacts the slotted spring pin(7)and lifts the valve seal(16)from the float piston(6). This allows the brake fluid to return to the supply reservoir,releasing the pressure in the brake system.131415 between the master cylinder and the rest of the brakecomponent is the key to safe, reliable brake system operationconditions.in dynamic forces from rear to front accompanies thebraking‐process braking.However this rear to front weight shift is not a linear process,but its magnitude increases as a function of deceleration.Thus the need for a supplementary means of reducing the brakepressure at the rear wheels relative to that at the front wheels.This function is assumed by the brake‐pressure regulating valve, that(as a function of manufacturer and vehicle) it willy gusually conform to one of three designs:‐load‐sensitive pressure‐regulating valve,‐pressure‐sensitive pressure‐regulating valve,‐deceleration‐sensitive pressure‐regulatingvalve.16It is required for the vehicles(such as stationwagons)in which high load factors lead topronounced inter‐axle force shifts duringbraking.gThe pressure regulator is attached to thevehicle body,and connected to the rearsuspension via mechanical linkage.The relative displacement from suspensionand body is relayed to a piston located withinthe pressure‐regulating valve’s housing.The piston responds to variations insuspension compression rates by contracting ai i t b t tispring to modify the cycle point.This system adapts the pressure at the rearbrakes to compensate the load changingconditions.1718It is also known like pressure limiters.pIt is employed on vehicles in which thepotential for inter‐axle load shifts isrestricted by limited cargo capacity and alow center of gravity(i.e.sports cars).19It is used in a wide variety ofapplications.The cycle point in these devises,determined by the vehicle’s rate ofdeceleration,that is generally0.3g.The valve incorporates compensationproperties.2021AccumulatorPumpElectrovalve22The EHB is a braking system that combines the functions of a brake servo unit and the ABS equipment including ESP.Mechanical operation of the brake pedal is detected by the actuation unit by means of electronic sensor with redundant backup and a signal is transmitted to the ECU.23。