(完整版)汽车制动系统英文文献及翻译)

Automobile Brake System

The braking system is the most important system in cars. If the brakes fail, the result can be

disastrous.

Brakes

are

actually

energy

conversion

devices,

which

convert

the

kinetic

energy

(momentum)

of

the

vehicle

into

thermal

energy

(heat).When

stepping

on

the

brakes,

the

driver

commands

a

stopping

force

ten

times

as

powerful

as

the

force

that

puts

the

car

in motion.

The

braking system can exert thousands of pounds of pressure on each of the four brakes.

Two complete independent braking systems are used on the car. They are the service brake

and the parking brake.

The

service

brake

acts

to

slow,

stop,

or

hold

the

vehicle

during

normal

driving.

They

are

foot-operated by the driver depressing and releasing the brake pedal. The primary purpose of the

brake is to hold the vehicle stationary while it is unattended. The parking brake is mechanically

operated by when a separate parking brake foot pedal or hand lever is set.

The

brake

system

is

composed

of

the

following

basic

components:

t

he

“master

cylinder”

which

is

located

under

the

hood,

and

is

directly

connected

to

the

brake

pedal,

converts

driver

foot’s mechanical pressure into hydraulic pressure. Steel “brake lines” and flexible “brake hoses”

connect the master cylinder to the “slave

cylinders” located at each wheel. Brake fluid, specially

designed to work in extreme conditions, fills the system. “Shoes” and “pads” are pushed by the

slave cylinders to contact the “drums” and “rotors” thus causing drag, which (hopefully) slows the

car.

The typical brake system consists of disk brakes in front and either disk or drum brakes in the

rear

connected

by

a

system

of

tubes

and

hoses

that

link

the

brake

at

each

wheel

to

the

master

cylinder (Figure).

Basically,

all

car

brakes

are

friction

brakes. When

the driver

applies

the

brake,

the

control

device

forces

brake

shoes,

or

pads,

against

the

rotating

brake

drum

or

disks

at

wheel.

Friction

between the shoes or pads and the drums or disks then slows or stops the wheel so that the car is

braked.

In most modern brake systems (see Figure 15.1), there is a fluid-filled cylinder, called master

cylinder, which contains two separate sections, there is a piston in each section and both pistons

are connected to a brake pedal in the driver’s compartment. When th

e brake is pushed down, brake

fluid is sent from the master cylinder to the wheels.

At the wheels, the fluid pushes shoes, or pads, against revolving drums or disks. The friction

between

the

stationary

shoes,

or

pads,

and

the

revolving

drums

or

disks

slows

and

stops

them.

This slows or stops the revolving wheels, which, in turn, slow or stop the car.

The brake fluid reservoir is on top of the master cylinder. Most cars today have a transparent r

reservoir so that you can see the level without opening the cover. The brake fluid level will drop

slightly as the brake pads wear. This is a normal condition and no cause for concern. If the level

drops

noticeably

over

ashort

period

of

time

or

goes

down

to

about

two

thirds

full,

have

your

brakes checked as soon as possible. Keep the reservoir covered except for the amount of time you

need to fill it and never leave a cam of brake fluid uncovered. Brake fluid must maintain a very

high boiling point. Exposure to air will cause the fluid to absorb moisture which will lower that

boiling point.

The brake fluid travels from the master cylinder to the wheels through a series of steel tubes

and reinforced rubber hoses. Rubber hoses are only used in places that require flexibility, such as

at

the

front

wheels,

which

move

up

and

down

as

well

as

steer.

The

rest

of

the

system

uses

non-corrosive

seamless

steel

tubing

with

special

fittings

at

all

attachment

points.

If

a

steel

line

requires a repair, the best procedure is to replace the compete line. If this is not practical, a line

can be repaired using special splice fittings that are made for brake system repair. You must never

use copper tubing to repair a brake system. They are dangerous and illegal.

Drum brakes, it consists of the brake drum, an expander, pull back springs, a stationary back

plate, two shoes with friction linings, and anchor pins. The stationary back plate is secured to the

flange of the axle housing or to the steering knuckle. The brake drum is mounted on the wheel hub.

There is a clearance between the inner surface of the drum and the shoe lining. To apply brakes,

the driver pushes pedal, the expander expands the shoes and presses them to the drum. Friction

between the brake drum and the friction linings brakes the wheels and the vehicle stops. To release

brakes,

the

driver

release

the

pedal,

the

pull

back

spring

retracts

the

shoes

thus

permitting

free

rotation of the wheels.

Disk brakes, it has a metal disk instead of a drum. A flat shoe, or disk-brake pad, is located on

each side of the disk. The shoes squeeze the rotatin g disk to stop the car. Fluid from the master

cylinder forces the pistons to move in, toward the disk. This action pushes the friction pads tightly

against

the

disk.

The

friction

between

the

shoes

and

disk

slows

and

stops

it.

This

provides

the

braking action. Pistons are made of either plastic or metal. There are three general types of disk

brakes.

They

are

the

floating- caliper

type,

the

fixed-caliper

type,

and

the

sliding- caliper

type.

Floating- caliper and sliding-caliper disk brakes use a single piston. Fixed-caliper disk brakes have

either two or four pistons.

The brake system assemblies are actuated by mechanical, hydraulic or pneumatic devices. The

mechanical leverage is used in the parking brakes fitted in all automobile. When the brake pedal is

depressed, the rod pushes the piston of brake master cylinder which presses the fluid. The fluid

flows

through

the

pipelines

to

the

power

brake

unit

and

then

to

the

wheel

cylinder.

The

fluid

pressure expands the cylinder pistons thus pressing the shoes to the drum or disk. If the pedal is

released, the piston returns to the initialposition, the pull back springs retract the shoes, the fluid is

forced back to the master cylinder and braking ceases.

The

primary

purpose

of

the

parking

brake

is

to

hold

the

vehicle

stationary

while

it

is

unattended.

The

parking

brake

is

mechanically

operated

by

the

driver

when

a

separate

parking

braking hand lever is set. The hand brake is normally used when the car has already stopped. A

lever is pulled and t

he rear brakes are approached and locked in the “on” position. The car may

now be left without fear of its rolling away. When the driver wants to move the car again, he must

press a button before the lever can be released. The hand brake must also be able to stop the car in

the event of the foot brake failing. For this reason, it is separate from the foot brake uses cable or

rods instead of the hydraulic system.

Anti-lock Brake System

Anti-lock

brake

systems

make

braking

safer

and

more

convenient,

Anti-lock

brake

systems

modulate brake system hydraulic pressure to prevent the brakes from locking and the tires from

skidding on slippery pavement or during a panic stop.

Anti-lock

brake

systems

have

been

used

on

aircraft

for

years,

and

some

domestic

car

were

offered with an early form of anti-

lock braking in late 1990’s. Recently, several automakers have

introduced more sophisticated anti-lock system. Investigations in Europe, where anti-lock brakin g

systems have been available for a decade, have led one manufacture to state that the number of

traffic accidents could be reduced by seven and a half percent if all cars had anti-lock brakes. So

some sources predict that all cars will offer anti-lock brakes to improve the safety of the car.

Anti-lock systems modulate brake application force several times per second to hold the tires

at a controlled amount of slip; all systems accomplish this in basically the same way. One or more

speed

sensors

generate

alternating

current

signal

whose

frequency

increases

with

the

wheel

rotational

speed.

An

electronic

control

unit

continuously

monitors

these

signals

and

if

the

frequency of a signal drops too rapidly indicating that a wheel is about to lock, the control unit

instructs

a

modulating

device

to

reduce

hydraulic

pressure

to

the

brake

at

the

affected

wheel.

When

sensor

signals

indicate

the

wheel

is

again

rotating

normally,

the

control

unit

allows

increased hydraulic pressure to the brake. This release-apply cycle occurs several time per second

to “pump” the brakes like a dr

iver might but at a much faster rate.

In addition to their basic operation, anti-lock systems have two other things in common. First,

they do not operate until the brakes are applied with enough force to lock or nearly lock a wheel.

At all other times, the system stands ready to function but does not interfere with normal braking.

Second, if the anti- lock system fail in any way, the brakes continue to operate without anti-lock

capability. A warning light on the instrument panel alerts the driver when a problem exists in the

anti-lock system.

The

current

Bosch

component

Anti-lock

Braking

System

(ABS

Ⅱ

),

is

a

second

generation

design wildly used by European automakers such as BWM, Mercedes- Benz and Porsche. ABS

Ⅱ

system consists of : four wheel speed sensor, electronic control unit and modulator assembly.

A speed sensor is fitted at each wheel sends signals about wheel rotation to control unit. Each

speed sensor consists of a sensor unit and a gear wheel. The front sensor mounts to the steering

knuckle

and

its

gear

wheel

is

pressed

onto

the

stub

axle

that

rotates

with

the

wheel.

The

rear

sensor mounts the rear suspension member and its gear wheel is pressed onto the axle. The sensor

itself is a winding with a magnetic core. The core creates a magnetic field around the winding, and

as

the

teeth

of

the

gear

wheel

move

through

this

field,

an

alternating

current

is

induced

in

the

winding.

The

control

unit monitors

the

rate

o

change in

this

frequency

to

determine

impending

brake lockup.

The control unit’s functi

on can be divided into three parts: signal processing, logic and safety

circuitry. The signal processing section is the converter that receives the alternating current signals

form the speed sensors and converts them into digital form for the logic section. The logic section

then analyzes the digitized signals to calculate any brake pressure changes needed. If impending

lockup is sensed, the logic section sends commands to the modulator assembly.

Modulator assembly

The

hydraulic

modulator

assembly

regulates

pressure

to

the

wheel

brakes

when

it

receives

commands from the control utuit. The modulator assembly can maintain or reduce pressure over

the

level

it

receives

from

the

master

cylinder,

it

also

can

never

apply

the

brakes

by

itself.

The

modulator assembly consists of three high-speed electric solenoid valves, two fluid reservoirs and

a

turn

delivery

pump

equipped

with

inlet

and

outlet

check

valves.

The

modulator

electrical

connector and controlling relays are concealed under a plastic cover of the assembly.

Each front wheel is served by electric solenoid valve modulated independently by the control

unit.

The

rear

brakes

are

served

by

a

single

solenoid

valve

and

modulated

together

using

the

select- low

principle.

During

anti-braking

system

operation,

the

control

unit

cycles

the

solenoid

valves to either hold or release pressure the brake lines. When pressure is released from the brake