8/7/2019 Gears (2)

1/46

8/7/2019 Gears (2)

2/46

Introduction

Gear typesGear Assemblies

Velocity ratio

Gear manufacturingGearbox

8/7/2019 Gears (2)

3/46

Gears are the most common means used for power transmission.

They can be applied between two shafts which are:Parallel

Perpendicular and intersecting

Perpendicular and non-intersecting

8/7/2019 Gears (2)

4/46

Gears are made to high precision.

However it is necessary to design for a specific application so that

proper selection can be made.

Used to be called toothed wheels dating back to 2600 b.c.

8/7/2019 Gears (2)

5/46

8/7/2019 Gears (2)

6/46

8/7/2019 Gears (2)

7/46

8/7/2019 Gears (2)

8/46

Most common form.

Used for parallel shafts.

Suitable for low to medium speedapplication.

Relatively high ratios can be

achieved (< 7).

Steel, brass, bronze, cast iron, andplastics.

Can also be made from sheet metal.

8/7/2019 Gears (2)

9/46

8/7/2019 Gears (2)

10/46

8/7/2019 Gears (2)

11/46

Used for parallel shafts.

Teeth engage gradually reducing shocks.

Teeth are at an angle .

8/7/2019 Gears (2)

12/46

Helix angle 7 to 35 degrees.

Helix angle must be the same for

both the mating gears.Used in automobiles.

More smooth and quiet operation.

More power.

Larger speeds.Produces axial thrust which is a

disadvantage.

8/7/2019 Gears (2)

13/46

A herringbone gear, also known

as a double helical gear.

To avoid axial thrust, twohelical gears of opposite hand can

be mounted side by side, to cancel

resulting thrust forces

Herringbone gears are mostlyused on heavy machinery.

8/7/2019 Gears (2)

14/46

They have conical shape.Bevel gears are useful when the direction of a shaft's rotation

needs to be changed .They are usually mounted on shafts that are 90 degrees apart, butcan be designed to work at other angles as well.

8/7/2019 Gears (2)

15/46

8/7/2019 Gears (2)

16/46

Straight bevel gears

Hypoid bevel gears

Spiral bevel gears

8/7/2019 Gears (2)

17/46

For large speed reductions between two perpendicular and non-

intersecting shafts.

Driver called worm looks like a thread.

8/7/2019 Gears (2)

18/46

8/7/2019 Gears (2)

19/46

Rack and pinion gears are

used to convert rotation

(F

rom the pinion) into linearmotion (of the rack)

A perfect example of this

is the steering system onmany cars

8/7/2019 Gears (2)

20/46

Identified based on the input and output shaft positions:

Parallel shaft Perpendicular shaft Other types

Spur gears Bevel gears Rack-and-pinion

Heical gears Worm gears

8/7/2019 Gears (2)

21/46

1

2

1

2

d

d

N

N!i =

Velocity ratio is defined as the ratio of rotational speed of the input gear

to that of the output gear

8/7/2019 Gears (2)

22/46

8/7/2019 Gears (2)

23/46

Methods ofManufacturing Gears

Forming the gear teeth by using milling

Generating the gear teeth by gear shaping

Generating the gear teeth by gear hobbing

8/7/2019 Gears (2)

24/46

GEARMILLING

8/7/2019 Gears (2)

25/46

GEAR SHAPING GEAR HOBBING

8/7/2019 Gears (2)

26/46

8/7/2019 Gears (2)

27/46

A transmission or gearbox provides speed and

torque conversions from a rotating power source to

another device using gear ratios.

8/7/2019 Gears (2)

28/46

Basic types of gearboxes:

Parallel shaft gearbox.

Planetary gearbox.

8/7/2019 Gears (2)

29/46

Manufactured from either cast iron or aluminium, the casing must be strong to

withstand the lateral forces generated, as power flows between gear clusters

The transmission housing must be able to support and secure the various

shafts and components in the transmission system. Precision bores, faces and

grooves are used to house the bearings &washers.

8/7/2019 Gears (2)

30/46

Because manual transmissions operate at high speeds, gears can easily

overheat. Lubrication is needed to ensure smooth and durable operation.

Fillerplug

Drain

plug

Typical oillevel

The transmission casing, contains the lubrication required for the gearing.

A filler plug in the side and a drain plug underneath, enable the oil to be

topped up and changed.

8/7/2019 Gears (2)

31/46

The input shaft, also known as theclutch shaft, has a

splined end that is directly connected to the clutch plate.Clutch rotation is directly transferred to the input shaft.

The input shaft is supported by a bearingfitted to a shoulder and pressed into the

transmission casing.

A single gear is used to drive the counter shaft. Cone and

synchronizer teeth may be incorporated for engaging theoutput shaft to the input shaft.

Splines

Bearing

shoulder

Synchronizerteeth

Helical gear

Cone

8/7/2019 Gears (2)

32/46

Inputshaft

Outputshaft

Counter shaft

Thrustwasher

Thrust washer

The counter shaft gear consists of a cluster of various gears, all rotating at the same speed,and continuously meshed with the gears on the input and output shafts.

The counter shaft always turns in the opposite direction from the input shaft. It often runs

the length of the transmission case and uses thrust washers to limit sideways motion of thegear.

8/7/2019 Gears (2)

33/46

When selecting reverse, the

direction of drive is changed. This isachieved by using an idler gear.

The idler gear is meshedbetween a counter shaft

gear and an output shaftgear.

Construction is generally agear on a fixed shaft,which is supported by

bushes or roller/needlebearings.

Reverse

idler gear

Input shaft Outputshaft

Reverseidler gear

Countershaft

Reverseshaft (fixed)

8/7/2019 Gears (2)

34/46

Smooth and precise gear selection is carried out usingsynchronizers. These

prevent the clashing or crunching of gears.

Each synchronizer is normally used to select one of two different gears.The synchronizers are held in place by splines on the output shaft, so they

rotate with the shaft.

The output shaft, also called themain shaft, is connected to the drive shaft.

Casing supports, used in conjunction with bearings, hold the shaft in place.

Different sized gears are mounted on the output shaft.

These gears rotate freely on the output shaft, and are meshed with the gears

of the counter shaft.

8/7/2019 Gears (2)

35/46

Outputshaft

1stgear

Bush

2nd & 1stsynchronizer

2nd gearblocking ring

2nd gear

Bush

3rd gear

4th and 3rd gearsynchronizer

4th gear

blockingring

8/7/2019 Gears (2)

36/46

36 of 27

Selector forks are used to move the

synchronizer sleeves into therequired positions. The number of

forks varies with the number of

gears.

The selector forks are moved byselector rods (rails). The drivers gear

lever controls the selector rods.

When the driver selects a leverposition, this transfers themovement to the selector forks,

which in turn move thesynchronizer sleeves.

l ctorro s

l ctor fork

l ctorfork

8/7/2019 Gears (2)

37/46

37 of 27

Selectorrod

Detents

Selector forks

Selectorpins

Fork

Pivot

There are two main types of linkages: external and internal. These connect the drivers gear

lever to the selector rods and forks.

Various configurations of linkage are used depending on the position of the transmission inrelation to the lever (for example, rear wheel drive or front wheel drive vehicles).The diagram above shows a single rail selector that uses one selector rod. The rod has fixed pins

to move the selector forks. The gate is formed by extensions of the selector forks. To select agear, the rail is rotated until the selector pin aligns with the required selector fork and then

moved backwards or forwards.

8/7/2019 Gears (2)

38/46

38 of 27

Multi-rail selection uses selector rods sliding in

the gearbox housing. Sliding with these rods arethe selector forks, which fit onto the synchronizer

sleeves.

Pushing a selector fork will move the outersleeve of the synchronizer hub to engage

the selected gear.

Shiftlever

Selector

gates

Selector

rods

Selector

forks

he lower end of the gear lever

moves between the three selectorgates to align with one rod.

hen the gear lever is moved

forward or backward, theselector rod and fork move

laterally.

8/7/2019 Gears (2)

39/46

39 of 27

Neutral

When the shift lever is in the neutral position, the gears on the input shaft,countershaft and output shaft spin at engine speed, however, none of the gears

are engaged to the output shaft, so there is no drive.

Input Output

8/7/2019 Gears (2)

40/46

40 of 27

1st Gear

The diagram shows the power flow from input to output when1st gear is selected.

Input Output

8/7/2019 Gears (2)

41/46

41 of 27

2nd Gear

The diagram shows the power flow from input to output when2nd gear is selected.

Input Output

8/7/2019 Gears (2)

42/46

42 of 27

3rd Gear

The diagram shows the power flow from input to outputwhen 3rd gear is selected.

Input Output

8/7/2019 Gears (2)

43/46

43 of 27

4th Gear

The diagram shows the power flow from input to output when 4th gear isselected. Connects the input shaft to the main shaft, giving direct drive (1:1).

Input Output

8/7/2019 Gears (2)

44/46

44 of 27

5th Gear

The diagram shows the power flow from input to output when5th gear is selected, giving overdrive.

Input Output

8/7/2019 Gears (2)

45/46

45 of 27

The diagram shows the power flow from input to output when reverse idler gearis selected, changing the direction of rotation of the output shaft.

Reverse Gear

Input Output

8/7/2019 Gears (2)

46/46