unit 5 a

The engine drivetrain system of the automobile consists of the engine, clutch, transmission, drive shaft, differential and driven wheels.. When the clutch pedal is in the released posit

ENGLISH FOR AUTOMOBILE

INDUSTRY

MASTER VO ANH TUAN

UNIT 5: The Drivetrain

The engine drivetrain system of the automobile consists of the engine, clutch, transmission, drive shaft, differential

and driven wheels We have already discussed the SI engine

and we know that it provides the motive power for the automobile Now let’s examine the clutch, transmission, drive shaft and differential in order to understand the roles of these devices.

The clutch allows the driver to engage or

disengage the engine and manual transmission or transaxle When the clutch pedal is in the released position, the clutch

locks the engine flywheel and the transmission input shaft together This causes engine power to rotate the transmission gears

and other parts of the drive train to propel the

vehicle When the driver presses the clutch pedal, the clutch disengages power flow and

the engine no longer turns the transmission

input shaft and gears.

The transmission uses various gear combinations, or ratios, to

multiply engine speed and torque to accommodate driving conditions

Low gear ratios allow the vehicle to accelerate quickly High gear ratios permit lower engine speed, providing good gas mileage.

A manual transmission lets the driver change gear ratios to better accommodate driving conditions An automatic transmission, on the

other hand, does not have to be shifted by the driver It uses an

internal hydraulic system and, in most cases, electronic controls to shift gears The input shaft of an automatic transmission is connected

to the engine crankshaft through a torque converter (fluid coupling) instead of a clutch.

Manual transmission

A manual transmission uses gears and shafts to achieve various gear ratios The speed of the output shaft compared to the speed of the input shaft varies in

each gear position This allows the driver to change the amount of torque going to

the drive wheels In lower gears, the car accelerates quickly When in high gear,

engine speed drops while vehicle speed stays high for good fuel economy

Automatic transmission

 An automatic transmission,

on the other hand, does not have to be shifted by the driver

It uses an internal hydraulic

system and, in most cases,

electronic controls to shift gears The input shaft of an automatic transmission is connected to the engine

crankshaft through a torque

instead of a clutch.

and directs it through the transmission.

The torque converter automatically engages and disengages power from the engine to the transmission in relation to engine rpm With the engine running at the correct idle speed, there is not enough fluid flow for power transfer through the torque converter As engine speed is increased, the added fluid flow creates sufficient force to transmit engine power through the torque converter assembly to the transmission.

Fluid travel inside the torque

converter:

(A) Fluid at rest in the mpeller/pump; (B) fluid thrown up and outward by the spinning pump;

and (C) fluid flow harnessed by the turbine and redirected back into the pump

Drive Shaft

The drive shaft, or propeller shaft, transfers power from the

transmission to the rear axle assembly It is a hollow metal tube with two

or more universal (swivel) joints The universal joints allow the rear

suspension to move up and down without damaging the drive shaft.

The differential serves three purposes:

• The most obvious is the right angle transfer of the rotary motion of the

drive shaft to the wheels.

• The second purpose is to allow each driven wheel to turn at a

different speed This is necessary because the “outside” wheel must

turn faster than the “inside’’ wheel when the vehicle is turning a corner.

• The third purpose is the torque increase provided by the gear ratio.

This gear ratio can be changed in a repair shop to allow different torque to be delivered to the wheels while using the same engine and transmission The gear ratio also affects fuel economy

Suspension, Steering, and Brake Systems

Suspension, Steering, and Brake Systems

Suspension System

The suspension system

allows the vehicle’s wheels

and tires to move up and

down with little effect on

body movement This makes

the vehicle’s ride smooth and

safe The suspension system

also prevents excessive

body lean when turning

corners quickly

A spring is the core of all

suspension systems Springs carry

the weight of the vehicle and absorb

shock forces while maintaining correct

riding height They are compressible links between the vehicle’s frame and body and the tires Doing this, they

dampen road shock and provide a

comfortable ride If a spring is worn or damaged, other suspension parts will shift out of their proper positions and will experience increased wear.

Leaf spring

A leaf spring is fixed to the axle by U-bolts that clamp the centre of the stack of steel strips As the spring deflects , its leaves flatten, make greater contact with one another and stiffen the spring As the leave flattens, it lengthens so one end has a pivoted shackle

Coil spring

A coil spring is made of resilient steel rod It extends as the wheel moves down and compresses as the wheel moves up, so the car body remains reasonably level

Steering system

The steering system

allows the driver to

control vehicle

direction by turning

the wheels right or

left It uses a series of

gears, swivel joints,

and rods to do this.

Steering system

The steering system converts

the rotation of the steering wheel

into a swivelling movement of the

road wheels in such a way that the steering-wheel rim turns a long way to move the road wheels a short way

There are two steering systems

in common use - the rack and pinion and the steering box.

Brake system

The brake system converts the momentum of the vehicle into heat

by slowing and stopping the vehicle’s wheels This is done by

causing friction at the wheels The application of the friction units is

controlled by a hydraulic system

The brake system produces friction to slow or stop the vehicle When the driver presses the brake pedal, fluid pressure actuates a brake mechanism at each wheel These mechanisms force friction

material (brake pads or shoes) against metal discs or drums to slow wheel rotation

When the brake pedal

is pressed, pressure is

placed on a confined fluid The fluid pressure

transfers through the system to operate the brakes

An emergency brake is

a mechanical system

that applies the rear wheel brakes.