畢業(yè)設(shè)計(jì)(論文)外文文獻(xiàn)翻譯要求及封面-資料下載頁
2025-06-22 12:02本頁面
【正文】 applied, the control box senses the decrease in rear wheel speed, and activates the dump valve(s) if the rate of deceleration exceeds a predetermined limit.The control box energizes the dump valve with a series of rapid pulses to bleedoff wheelhydraulicpressure.Continuing in antilock mode, the dump valve is pulsed to keep the wheels rotating, while maintaining controlled deceleration.At the end of such a stop, the valve deenergizes and any fluid in the accumulator is returned to the master cylinder.Normalbrakeoperation resumes.FOUNDATION BRAKESFoundationbrakesinhydraulicsystems can be either drum or disc.In many applications, discs are used on the front axle and drums on the rear.Drumbrakesare said to be selfenergizing.That39。s because when thebrakeshoes expand and contact a rotating drum, the leading, or forward,brakeshoe is pushed against the trailing shoe by the force of the moving drum.This results in higher liningtodrum pressure than would be produced by the wheel cylinder alone.Asbrakelinings wear, the shoes periodically must be moved closer to the drums to ensure proper contact during braking.While some older drumbrakeassemblies are manually adjusted, most are automatic.These use a star wheel or ratchet assembly, which senses when the wheel cylinder has traveled beyond its normal stroke, and expands the pivot point at the other end of thebrakeshoes.In addition to being one of the friction elements, thebrakedrum or rotor also acts as a heat sink.It must rapidly absorb heat during braking, and hold it until it can be dissipated into the air.The heavier a drum or rotor is, the more heat it can hold.This is important, since the hotter thebrakelinings get, the more susceptible they are to heat fade.Heat fade is induced by repeated hard stops and results in reduced liningtodrum/rotor friction and increased vehicle stopping distance.As a rule, highquality linings will display less heat fade than inferior ones.Also, discbrakesare far more resistant to heat fade than drumbrakes.Another type of fade thatbrakesare susceptible to is water fade.Drumbrakes, with their large surface areas, apply fewer pounds per square inch of force between lining and drum during a stop than discbrakes.This, added to the drum39。s waterretaining shape, promotes hydroplaning between shoe and drum under wet conditions.The result is greatly increased stopping distance.Discbrakes, with their smaller friction surfaces and high clamping forces, do a good job of wiping water from rotors, and display little reduction in stopping capability when wet.有用的產(chǎn)品氣動(dòng)鋼瓶
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