英语翻译
Basically.brakes are devices for controlling the flow of motion in machines,and in this respect they resemble clutches; clutches start the flow while brakes arrest it.Before the engagement of a clutch or a brake,one of the two members in the device is moving while the other is stationary) after the engagement of a clutch both members are moving at the same speed.while after the application of a brake the moving member is either slowed down or stationary.In both cases the desired effects are produced by devices that are so alike,structurally,that they can sometimes serve in either capacity.
In arresting the motion of bodies,brakes must be capable of absorbing kinetic energy.Even when acting on translating bodies (like automobiles) most brakes are designed to act on rotating mechanical elements and to absorb energy either mechanically,hydraulically,or electrically.Mechanical brakes are the most common; they dissipate kinetic energy in the form of heat generated by mechanical friction between a rotating metallic element and a non-rotating friction element,when they are brought into contact by either mechanical,hydraulic ,pneumatic,or electrical means.The material in the friction element may be organic,metallic,or ceramic.Organic materials with an asbestos bases are satisfactory for the majority of applications.When service requirements are severe,however,the heat generted may cause "fading" (a drop in braking effectiveness caused by a reduction in the coefficient of friction).In such cases sintered metallic linings are prefered because of their high thermal conductivity and freedom from fading.By adding ceramic particles to sintered metallic linings,extremely hard and fade-resistant linings can be produced.
The rotating element in a mechanical brake is either a drum,a disk,or a series of disks.The nonrotating friction element in a drum brake may be either a band or a pair of shoes (blocks) that contract around the outside of the drum or a pair of shoes that expand against the inside of the drum.A disk brake may be similar to a plate clutch,with alternate rotating metallic and nonrotating friction elements,or it may be of the caliper type,with a single rotating disk and two opposed friction pads that squeeze the disk between them in a pinching action.