Gears

Lekce 1: Gears

Kapitola 1: Gears

Description
A gear is a component used to transmit a force from one device to another. Unlike pulley, gears are wheels which have teeth (or cogs), which fit into to teeth of another wheel. Thus the rotational torque can be transferred without any slippage. Various gears can transmit forces from the power source at different speeds or in different directions. The cog wheels usually interlace with another cog wheel, but in fact any device with compatible teeth can be used, such as linear racks.
The most important feature of gears is that various wheels with different diameters can be combined. Thus the rotational speed of the second cog wheel gets higher or lower. Colloquially the term "gear" is also used to refer to a particular arrangement of gears, and so we can hear collocations like "first gear" or "the car has five gears" etc.
Types of gears
External gear - its teeth are formed on the outer surface
Internal gear - its teeth are formed on the inner surface
 
 
Spur gears ("straight-cut gears") - the simplest and most common type in the form of a cylinder or a disk with the teeth projecting radially; the egde of each tooth is straight and parallel to the axis of rotation.
Helical gears - the edges of the teeth are not parallel to the axis of rotation, but they are set in a certain angle and because the gear is curved, the tooth looks like a part of a helix. Helical gear work more smoothly and quietly than spur gears.
Herringbone gears (also called double helical gears) - gears with two sets of teeth in the V shape; their advantage in comparison to helical gears is that they can withstand axial load
Bevel gears - a type of gears, which is conically shaped; they are most often mounted on shafts that are 90 degrees apart, but can be designed to work at other angles too.
 
Epiclic gearing- a system consisting of one or more outer gears, (called planet gears), which revolve about a central gear (called the sun). Planet gears are usually mounted on a movable arm (called carrier) which also can rotate relative to the sun gear.
 
Vocabulary
gear - ozubený převod
transmit - přenést
force - síla
device - zařízení; součástka
pulley - řemenice
cog - zub na ozubeném kole
cog wheel - ozubené kolo
torque - kroutivá síla, kroutivý moment
slippage - prokluzování
interlace - prolínat se
rack - ozubnice
diameter - poloměr
rotational speed - rotační rychlost
first gear - první rychlost, jednička (v automobilu)
spur gear - čelní ozubený převod
cylinder - válec
radially - paprskovitě
edge - okraj
axis of rotation - osa rotace
helical gear - šnekový převod
herringbone gears - převod se šípovým ozubením
bevel gear - kuželočelní převod
conically - kuželově
mount - namontovat
shaft - hřídel
angle - úhel
epiclic gearing - planetová převodovka
revolve - otáčet se
movable arm - pohyblivé rameno
relative to - vzhledem k
 
Obrázky a fotografie použité v této kapitole pochází ze stránek {Wikimedia Commons XH http://commons.wikimedia.org}, kde byly zveřejněny pod licencí {GNU FDL XH http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License}.     

Kapitola 2: Cvičení

  1. Studenti zpracují na téma Gears powerpointovou prezentaci.

Kapitola 3: Kontrolní otázky

  1. What does a typical gear look like?
  2. What types of gears do you know?
  3. What is the difference between external and internal gears?

Kapitola 4: Autotest

  1. What is the difference between gears and pulleys?



     
  2. What is the main role of the teeth?



     
  3. Which gears can be combined?



     
  4. What is the most common type of gears?



     
  5. What is the advantage of helical gears?



     

Lekce 2: Bevel gears

Kapitola 1: Bevel gears

Bevel gears are a type of gears, where the surfaces of cog-wheels are in the shape of a cone. The angle between the two wheels is usually 90 degrees, but they can be designed for other angles as well.
 
 
Description
 
Important terms to describe bevel gears are pitch surface and pitch angle. The pitch surface is an imaginary surface acquired by averaging the tops of the teeth (also called cogs) and the valleys between them. The angle between the pitch surface and the axis of the gear is called the pitch angle. Ordinary gears have the pitch surface in the shape of a cylinder, but pitch surfaces of bevel gears have to be conical.
 
Types of bevel gears
 
The pitch angles of the most common bevel gears are smaller than 90 degrees. In this case their teeth point outwards and therefore they are called external. If their pitch angles are more than 90 degrees, their teeth point inward and they are called internal. Occasionally the pitch angle can be exactly 90 degrees. Because the teeth are parallel with the axis of the gear and thus it resembles a crown, it is called a crown gear.
 
Vocabulary
 
bevel gears – kuželové soukolí
cog-wheel, gear – ozubené kolo
cone – kužel
conical – kuželový
shape – tvar
angle – úhel
degree – stupeň
surface – plocha, povrch
pitch surface – roztečná plocha
pitch angle – úhel roztečného kužele
imaginary – myšlený
average – průměr, průměrovat
cog – zub (na ozubeném kole)
axis – osa
cylinder – válec
point – směřovat
outwards – směrem ven
inwards – směrem dovnitř
external – vnější
internal – vnitřní
occasionally – příležitostně
parallel – rovnoběžný
crown gear – korunové kolo
 
Obrázky a fotografie použité v této kapitole pochází ze stránek Wikimedia Commons, kde byly zveřejněny pod licencí GNU FDL.   

Kapitola 2: Cvičení

  1. Studenti zpracují na téma Bevel Gears powerpointovou prezentaci.

Kapitola 3: Kontrolní otázky

  1. Can you describe bevel gears?
  2. What are their typical shapes?
  3. What types of bevel gears do you know?

Kapitola 4: Autotest

  1. What is the most common angle between two bevel gears?



     
  2. What is the pitch surface?


     
  3. What is the pitch angle



     
  4. What is the difference between pitch surfaces of ordinary gears and bevel gears?



     
  5. Which type of bevel gears is more common, external or internal?


     

Lekce 3: Worm drive

Kapitola 1: Worm drive

Worm drive is a gearing system consisting of a worm and some other type of a gear.
 
Description
 
The worms are a type of helical gears resembling a screw, which are usually quite long in the axial direction and have quite a large helix angle (often just little less than 90 degrees). The worm intermeshes with another gear, which is usually an ordinary gear in the shape of a disk. This combination allows to reach high gear ratio in a small space – while typical helical gears are usually limited to gear ratio maximum up to 10:1, worm drives can have the ratio much higher (usually up to 100:1, occasionally even 500:1). The main disadvantage with large helix angles is the sliding action, which causes that the efficiency of the drive is smaller than 90 per cent, sometimes even than 50 per cent.
The worms can differ according to the direction of the teeth twist. If the twist goes along the axis clockwise, it is called a right hand worm, if it goes anticlockwise, it is a left hand worm. The terminology is the same as with screws.
 
Direction of transmission
 
One of the differences between worm drive and most other types of gearing systems is that the direction of transmission is not reversible. This means that the worm can drive the gear, but the gear cannot drive the worm, because the friction in this direction is too high. This can be useful when we need to eliminate the reverse action. Such gear systems are called self-locking. The self-locking properties appear when the tangent of the helix angle is less than the coefficient of friction.
 
Vocabulary
 
worm drive – šnekový převod
worm – šnek
gearing system – převodový systém
gear – ozubené kolo
helical gear – kolo se spirálovým ozubením
resemble – podobat se
screw – vrut
in the axial direction – ve směru osy
helix angle – úhel stoupání šroubovice
intermesh – proplétat se
gear ratio – převodový poměr
disadvantage – nevýhoda
sliding – prokluz
efficiency – výkon
drive – pohon
differ – lišit se
teeth twist – zakřivení zubů
axis – osa
clockwise – ve směru hodinových ručiček
counterclockwise – proti směru hodinových ručiček
right hand worm – pravochodý šnek
left hand worm – levochodý šnek
friction – tření
reverse action – opačný chod
self-locking – samosvorný, samozajišťovací
property – vlastnost
tangent – tangens
coefficient – součinitel
 
Obrázky a fotografie použité v této kapitole pochází ze stránek {Wikimedia Commons XH http://commons.wikimedia.org}, kde byly zveřejněny pod licencí {GNU FDL XH http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License}. 

Kapitola 2: Cvičení

  1. Studenti zpracují na téma Worm Drive powerpointovou prezentaci.

Kapitola 3: Kontrolní otázky

  1. Can you describe a worm drive?
  2. How can the worms differ?
  3. What is their advantage in comparison with helical gears?

Kapitola 4: Autotest

  1. What is their usual helix angle?



     
  2. What does the worm usually intermesh with?



     
  3. What is the main disadvantage of big helix angle?



     
  4. What do right-hand worms look like?



     
  5. Why is this type of transmission not reversible?



     

Lekce 4: Planetary gears

Kapitola 1: Planetary gears

Planetary gearing, also called epicyclic gearing, is a system, where one or more outer gears revolve around one central gear.
 
Description 
The planetary gearing system consists of two or more gears. The central gear is called the sun, while the outer ones are called planet gears. Planet gears rotate around the sun gear on an arm, which can be stationary or movable as well. Sometimes the system is placed inside a ring gear, called annulus. Although the axes of the gears are usually parallel, some exceptions may occur. For example the gears used in some pencil sharpeners are placed at angle.
 
Gear ratio 
Usually, one of the components (sun, planetary carrier or annulus) is stationary, one of them is used as an input and the third one as an output. If the carrier is stationary, than the sun gear works as an input and planetary gears rotate around their axes. The gear ratio depends on the number of teeth of individual gears and can be calculated as i = −s/p, where s is the number of the sun gear teeth and p of the planet gear teeth. As an example we can take 24-tooth sun gear and 16-tooth planet gears. Then gr = −24/16 = −3/2. The minus sign means a change in the direction. In this case one three clockwise turns of the sun gear produce 2 counterclockwise turns of the planet gears. The rotation of the planet gears drives the annulus. Similarly, the gear ratio can be calculated gr = p/a, where a is the number of the teeth of the annulus.
 
Advantages and disadvantages 
The main advantage of planetary gearing is its small size, especially in comparison with quite big gear ratios. It is also very efficient with a very small loss of energy inside the gearbox. Its operating life is usually longer than the lifetime of other gear systems. Coaxial shafting can also be considered an advantage.
The main disadvantage is quite complex design, which makes it accessible only with difficulties. Its production is also much more expensive than the production of other types of gearing systems.
 
Vocabulary 
planetary gearing, epicyclic gearing – planetový převod
outer gear, planet gear – vnější ozubené kolo
central gear, the sun – vnitřní ozubené kolo
rotate – rotovat
stationary – nehybný
movable – pohyblivý
ring gear, annulus – ozubený věnec
axe – osa
pencil sharpener – ořezávátko na tužky
angle – úhel
carrier – nosič
input – přívod
output – výstup
gear ratio – převodový poměr, poměr převodových stupňů
ring gear – ozubený věnec
gear ratio – převodový poměr
clockwise turn – otáčka ve směru hodinových ručiček
counterclockwise turn – otáčka proti směru hodinových ručiček
drive – pohánět
advantage – výhoda
disadvantage – nevýhoda
efficient – výkonný
loss of energy – ztráta energie
gearbox – převodovka
operating life, lifetime – životnost
coaxial – souosý
shafting – hřídelové vedení
accessible – přístupný
production – výroba
 
Obrázky a fotografie použité v této kapitole pochází ze stránek {Wikimedia Commons XH http://commons.wikimedia.org}, kde byly zveřejněny pod licencí {GNU FDL XH http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License}. 

Kapitola 2: Cvičení

  1. Studenti zpracují na téma Planetary Gears powerpointovou prezentaci.

Kapitola 3: Kontrolní otázky

  1. Can you describe planetary gearing?
  2. Can you explain, what gear ratio means?
  3. What are the advantages and disadvantages of this system?

Kapitola 4: Autotest

  1. What does planetary gearing system look like?



     
  2. What is the central gear called?


     
  3. How can the gear ratio be calculated?



     
  4. What is one of its advantages?



     
  5. Its production



     

Lekce 5: Diferential

Kapitola 1: Differential

A differential is a device, which is capable to transmit torque and rotation through three shafts. This is usually achieved by the means of gears. It receives one input which results into two outputs. Sometime differentials work also the other way: two inputs are combined into one output, which is their difference.
 
 
Application
 
Differentials are usually applied in automobiles and other vehicles with the need to rotate their wheels at different speeds. This situation occurs especially when turning – the inner wheel travels a shorter distance and needs to be slower then the outer wheel, which travels a longer distance. Vehicles, such as karts, which have no differential, have to drag the outer wheel on the road surface when cornering, which makes their handling difficult, damages their wheels or tyres, powertrain, as well as roads.
 
Way of operation 
The differential is placed on the propeller shaft (also called the drive shaft), which receives the torque from the engine. A spiral bevel gear is driven by the end of the propeller shaft and meshes with a large crown gear. The crown gear is attached to a carrier, containing a small planetary gearing system. In this system, two sun gears (sharing the same axis with the crown gear) drive the half shafts with vehicles driven wheels. The sun gears also mesh with a planet gear on a perpendicular axis and changes orientation as the ring gear rotates. A lot of differentials have two planet gears opposite to each other (or even more).
If the resistance at both wheels of the vehicle is equal, the planet gear does not rotate, and both wheels run at the same speed. But if the resistance of one of the wheels is bigger, than part of the torque is transmitted onto the planet gear, which starts rotating and slows down the rotation of the particular half shaft.
 
Vocabulary 
differential – diferenciál
device – zařízení
capable – schopný
transmit – přenést
torque – točivý moment, kroutivá síla
shaft – hřídel
by the means of – prostřednictvím
gear – ozubené kolo
input – vstup
output – výstup
difference – rozdíl
turn corner
turning, cornering – zatáčení
inner – vnítřní
outer – vnější
distance – vzdálenost
application – použití
apply – použít
vehicle – vozidlo
kart – vozík
drag – táhnout
surface – povrch
handling – zacházení
damage – poškodit
tyre – pneumatika
powertrain – hnací ústrojí
propeller shaft (drive shaft) – hnací hřídel
spiral bevel gear – kuželové ozubené kolo se zakřivenými zuby
drive (drove, driven) – hnát, pohánět
crown gear – věncové ozubené kolo
planetary gearing system – planetární převodový systém
sun gear – centrální kolo
planet gear – planetové kolo
axis – osa
half shaft – hnací hřídel polonápravy, hnací poloosa
mesh – proplétat se
perpendicular – kolmý
resistance – odpor
equal – stejný
speed – rychlost
slow down – zpomalit
 
Obrázky a fotografie použité v této kapitole pochází ze stránek {Wikimedia Commons XH http://commons.wikimedia.org}, kde byly zveřejněny pod licencí {GNU FDL XH http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License}. 

Kapitola 2: Cvičení

  1. Studenti zpracují na téma Differential powerpointovou prezentaci.

Kapitola 3: Kontrolní otázky

  1. Can you describe a differential?
  2. How does it work?
  3. Where is it used?

Kapitola 4: Autotest

  1. How many shafts does a differential usually have?



     
  2. What is the main role of differentials?



     
  3. What problem do vehicles without a differential face?



     
  4. Where is the differential usually placed?



     
  5. Which of the following vehicles usually have a differential?



     

Lekce 6: Literatura