M. Ibbotson - Professional english in use engineering (794233), страница 24
Текст из файла (страница 24)
edge (near the front of the wing) acting as a pivot, while the(9) ................................ edge (at the rear) lifts, increasing the spoiler's (10) ................................. Spoilers serve adual purpose. Firstly, they generate (11) ................................ ,helping to push the aircraft down onto the runway.Secondly, they create (12) ................................ , increasing air resistance and helping to slow the aircraft down.Spoilers are therefore different to flaps, which are deployed from the rear of an aircraft's wings as itdescends and slows down before landing.
Flaps are rotated downwards, at a progressively increasing(13) .......... ...................... of ................................ , in order to provide increased lift at lower speedsOV~r .f-o ':fOtc ~Describe how a specific aircraft, vehicle or structure is affected by airflow. How does air flowaround it? Which aerodynamic issues do you think engineers needed to consider in its design?Professional English in Use Engineering85EDJ Engines and motors-Types and functions of engines and motorsThe term engine usually refers to petrol engines,diesel engines and jet engines (or jets) . In engineering,motor usually means electric motor - but in generallanguage, 'motor' can also refer to petrol and dieselengines. Engines and motors power (or drive) machinesby generating rotary motion- for example, to drivewheels.
In jet engines, compressors and turbines rotateto generate thrust - pushing force, produced by forcingair from the back of the engine at high velocity.A jet engineAs an engine produces a couple -rotary force - the moving parts of the machine it is drivingwill produce resistance, due to friction and other forces.
As a result, torque (twisting force)is exerted on the output shaft of the engine. Torque -calculated as a turning moment, innewton metres - is therefore a measure of how much rotational force an engine can exert.The rate at which an engine can work to exert torque is the power of the engine, measuredin watts. Although engineers normally calculate engine power in watts, the power of vehicleengines is often given in brake horsepower (bhp) .
This is the power of an engine's outputshaft measured in horsepower {hp)- a historic measurement of power (see Appendix Ill onpage 100) .Note: See the fo ll ow ing un its for more information: Unit 33 (turn in g moments), Unit 34 (rotarymotion), Unit 35 (power), and Unit 41 (shafts).BrE: petrol; ArnE: gasolineBrE: petrol engine; ArnE: gasoline engine-Internal combustion enginesPetrol and diesel engines are internal combustion engines. This means they are driven bythe combustion (burning) of fuel in enclosed, sealed spaces called combustion chambers. Inpetrol and diesel engines, the combustion chambers are cylinders surrounded by a cylinderblock and closed at the top by a cylinder head.
Each cylinder contains a piston. The numberof piston cylinders in an engine varies - engines in small motorcycles have only one, whilesports car engines may have twelve.Fuel is supplied to each cylinder from a tank. In most engines, the flow of fuel is generatedby a pump, which forces it- at high pressure - through fuel injectors. These vaporize thefuel, allowing it to mix with air. Using this mixture (of fuel and air), most engines functionas four-stroke engines. This means they work on a cycle of four stages - or four strokes. Astroke is an upward or downward movement of a piston.1 Induction or intakeThe intake valveopens. The mixtureenters the cylinderthrough a port(opening) in thecylinder head whilethe piston movesdownwards.2 Compression3 Power or ignition4 ExhaustThe intake valveThe spark plugThe exhaust valvecloses.
The piston _., produces a spark,_. opens, and the pistonmoves upwards,which ignitesmoves upwards, forcingcompressing the(lights) the mixture.the exhaust gases mixture.On ignition, thethose produced duringmixture explodes,combustion - out of thegenerating acylinder via the exhaustsudden pressureport. The exhaust valvewhich forces thethen closes and thepiston down.cycle begins again.The cycle of a four-stroke petrol engineNotes: See exe rcise 40.2 opposite for an ill ustra tion of a cylind er.See Un it 42 for more on cam, camshaft, co nnecting rod an d crankshaft.86Professional English in Use Engineering40.1Complete the text about diesel engines using words from A and B opposite.Diesel engines differ from (1) ................................
engines in one key respect: they are not fittedwith a (2) ................................ , in each cylinder, to ignite the fuel. This is because when a(3) ................................ of diesel and air is compressed inside a hot (4) ................................ , it willexplode spontaneously, without the need for a spark to provide (5) ................................. A dieselengine must therefore work in a way which prevents the diesel from exploding before thepiston is at the top of the cylinder.
To achieve this, the engine takes in only air during the(6) ................................ stage of the cycle. Therefore, during the (7) ................................ stage, onlyair- and not an air-fuel mixture - is pressurized. It is only at that last instant, when fullcompression has occurred, that the (8) ................................
above each cylinder forces vaporizeddiesel into the combustion chamber, where it ignites.Diesel engines operate at lower speeds than petrol engines, making them less suitable forhigh-speed applications. However, they are more able to (9) ................................ heavy vehicles,as they can produce greater amounts of (10) ................................ than petrol engines.40.2Look at the cross-section of an engine, and label it using words and expressions fromB opposite.4valve springcam5cooling water27 -·······-·"""''' """"'''""""''' ""''3 ......connecting rodOne cylinder of a four-stroke internal combustion engineOve,r 1-o ~:fotc01~Think about the engine in a vehicle you're familiar with. Describe specific aspects of it - thetype of fuel it uses, the llllmber of cylinders it has, and how much power and torque it produces.Professional English in Use Engineering87[II Transmission 1-GearsGear wheels, or gears, are wheels with teeth (or cogs).
The teeth interlock (fit together) with thoseof other gear wheels. When one gear wheel revolves, the other revolves with it - in the oppositedirection - as their teeth mesh together. Gears are normally fitted to sba&s. They transmit rotarymotion from one sha& to another - that is, they transmit drive.
Drive, usually supplied by anengine or motor, causes a shaft to revolve. A sha& connected directly to an engine or motor iscalled a drivesha& - or an input sha&. A gear wheel on a drivesha& is called a driver. The secondgear wheel, which meshes with the driver, is called a follower - the driver drives the follower.An assembly of several shafts and gear wheels is called a gear train or transmission system. Itbegins with an input shaft and ends with an output shaft. The system may contain idler gears(or idlers). These change the direction of a follower.-Gear ratiosGears can provide a mechanical advantage (see Unit 33) by using different gear ratios.
In thediagrams above, the driver has 20 teeth and the follower has 60 teeth. Therefore the driverrotates three times to make the follower rotate once. So the gear ratio is 3:1 (three to one).This means that if, for example, the input speed - that is, the speed of the driver- is 3,000rpm, the output speed (of the follower) will be 1,000 rpm.In some machines, a gearbox is used to provide a number of different gear ratios. Agearbox has a gear selection system, which allows gears to be changed (or shifted) while thetransmission is running. This may be a manual gearbox, where gears are changed by a person,or an automatic gearbox, which automatically selects a higher gear or lower gear, as needed.-Types of gear wheel•Spur gears are the simplest gears.
Theteeth run straight across the wheel.•Helical gears have curved teeth, so thatthey mesh together more smoothly.•Bevel gears allow drive to be transmittedthrough an angle- o&en 90°.•Crown gears transmit drive through 90°,often to a small gear called a pinion.•Worm gears transmit drive through anangle. They also allow a low outputspeed relative to the input speed ofthe worm.
They can provide a 'oneway' drive, as a worm can drive a gearbut a gear cannot drive a worm (themechanism will lock).worm gears88Professional English in Use Engineering41.1Change four words in the text below to make it correct. Look at A opposite to help you.An engine is connected to a driveshaft. Fitted to this output shaft is a gear wheel calledthe idler. As this gear wheel turns, it drives another gear wheel alongside it called a driver,which is fitted to an input shaft.41 .2Complete the text about continuously variable transmission using the words in the box.Look at A, B and C opposite to help you.a utomatichelicalhighermanualratioselectionshaftsshifttransmitwheelsCONTINUOUSLY VARIABLE TRANSMISSION (CVT)(1) ................................ gearboxes allow the driver of a vehicle to (2) ................................
gears as required.If a (3) ................................ gear is selected, the speed of the output shaft will increase relative tothe input shaft, for a given engine speed. In a typical (4) ................................ gearbox, however, thegear (5) ................................ system is automated, requiring no action by the driver. In addition, mostautomatic transmission systems use so-called planetary gears. In basic terms, these allow thetransmission to remain connected at all times - unlike manual gearboxes, in which pairs of(6) ................................
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
