University of Bahrain

College of Engineering

Department of Mechanical Engineering

Junior Project (MENG 290)

Gear Box

Transmission Fundamentals

Bashar Al-Tobul 20125667

Hammam Mohamed 20123973

Mahmoud Islam Elghoneimy 20124754

Salaar Shakeel 20122385

Semester II 2013/2014

Course Instructor: Dr. Noaman Bekheet

May 23, 2014

2

Table of Content |

Abstract.3

Introduction..4-9

Design Calculations and Drawings..9-14

Gearbox Operation.15-18

Comments and Conclusions.19

Appendix20

Reference.20

Acknowledgment.20

List of Figures |

Figure1 Spur gear.....5

Figure 2 Helical gear......6

Figure 3 Bevel gear...7

Figure 4 Worm gear....7

Figure 5 First Gear..15

Figure 6 Second Gear16

Figure 7 Third Gear.17

Figure 8 Fourth Gear.18

Figure 8 Reverse Gear..18

Figure 9 Stress Machine.20

The free-hand sketches and the AutoCAD drawing are attached to the report

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1.0 Abstract |

The objective of this project is to fully understand how a gearbox operates

and what the role of each component inside it is. Likewise, the dimensions of each

components are measured. The gearbox 5 transmissions are explained in details with

figures. Moreover, free hand sketches and AutoCAD drawings are attached for

further explanation. Difficulties faced during the project are also mentioned and

solutions and improvements are discussed.

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2.0 Introduction |

A gear is a machine element used to transmit motion between rotating

shafts/wheels when the center distance between the shafts is not too large. They

provide a positive drive, maintaining exact velocity ratios between driving and driven

shafts.

A transmission is a speed and power changing device installed at some point

between the engine and driving wheels of the vehicle. It provides a means for

changing the ratio between engine rpm (revolutions per minutes) and driving wheel

rpm to best meet each particular driving situation. Given in order to get smooth

starts and have power to pass and climb hills, a power ratio must be provided to

multiply the torque and turning effort of the engine. Also required is a speed ration

to avoid the need for extremely high engine rpm at high road speed. The

transmission is geared to perform these functions.

Power transmission gears are usually made from chromium molybdenum steel

which provides good toughness and resistance to wear. Some (low power) gears are

made from sintered metal (powered metal). Non-power gears can be made of

almost any material including composites for quieter running non lubricated

arrangements.

Most gears are run lubricated either by regular maintenance lubrication or by

being run semi submersed in oil or spray lubricated.

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2.1 Gears usage:

It plays an important role in our daily life basis, starting from our washing

machines in houses till the heavy vehicles in mining and construction places.

Accordingly for each machine or vehicle. Gears are simply a means of applying

leverage to rotating parts. A modern transmission provides both speeds and power.

The engineer who designed it selected the gear sizes that would give the best all

around performance. It is geared to a power ratio that puts the car in motion, and

then it shifts, or it shifted, to one or more speed ratios that keeps it rolling.

2.2 Types of gearboxes:

Different types of gearbox are used. These types are manual gear, automatic,

semi-automatic, and bicycle gearing. For each gearbox, several gears are utilized

such as spur, helical, bevel, hypoid and worm gears. Each type of gear is explained

briefly below:

Spur Gear

This is the most common type

of gear tooth shape, and

would be fitted in the

accessory gearbox of an

engine. The gear can be

formed either internally or externally. An internal gear would be used where

a change in speed is required without changing the axis of drive. External

spur gears are used where a change in speed is required but the shafts lie

Figure 1: Spur gears

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parallel to each other. Spur gears may be noisy owing to the impact of the

teeth upon each other as they rotate.

Helical Gear

This is a smoother, less noisy running gear than the spur gear, the teeth are

cut on a curve or helix, which produces a sliding engagement of the teeth, and more

than one tooth is in engagement at any one time. A disadvantage of this gear for is

that it produces a heavy axial load. This disadvantage can be eliminated by using

double helical gears, with the teeth being cut in an opposite helix. An advantage of

this type of gear is that it can accept and transmit a higher loading than a spur gear

of the same size. Helical gears might be fitted in the reduction gearbox of a turbo

prop engine or in the gearbox of an ordinary car.

Figure 2: Helical Gear

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Bevel Gear

This type of gear is used when the drive is required to be transmitted

through an angle; in this case the gear teeth can be straight cut or in a helical form,

when the axis of the shafts intersect. An example of use would be for the

transmission of drive from the main rotating assembly on a gas turbine to the

accessory gearbox, or the tail rotor gearbox on a helicopter.

Worm Gear

This gear form is used where there is a large resistance to turning,

and a large reduction in speed is required. The worm teeth are

similar to a multi start thread, and are cut at an angle or on the

skew, in which case the gear may be called a skew gear.

Figure 3: Bevel Gear

Figure 4: Worm Gear

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Automatic gear box : An automatic transmission (also called automatic

gearbox) is a type of motor vehicle transmission that can automatically

change gear ratios as the vehicle moves, freeing the driver from having to

shift gears manually. Most automatic transmissions have a defined set of

gear ranges, often with a parking pawl feature that locks the output shaft of

the transmission stroke face to keep the vehicle from rolling either forward

or backward. [2]

A semi-automatic transmission (SAT) (also known as a clutch-less manual

transmission, automated manual transmission, flappy-paddle gearbox,

or paddle-shift gearbox) is an automobile transmission that does not change

gears automatically, but rather facilitates manual gear changes by dispensing

with the need to press a clutch pedal at the same time as changing gears. It

uses electronic sensors, pneumatics, processors and actuators to

execute gear shifts on the command of the driver or by a computer. This

removes the need for a clutch pedal which the driver otherwise needs to

depress before making a gear change, since the clutch itself is actuated by

electronic equipment which can synchronize the timing and torque required

to make quick, smooth gear shifts. The system was designed by automobile

manufacturers to provide a better driving experience through fast overtaking

maneuvers on highways

Bicycle gearing: Bicycles usually have a system for selecting different gear

ratios. There are two main types: derailleur gears and hub gears. The

derailleur type is the most common, and the most visible,

using sprocket gears. Typically there are several gears available on the rear

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sprocket assembly, attached to the rear wheel. A few more sprockets are

usually added to the front assembly as well. Multiplying the number of

sprocket gears in front by the number to the rear gives the number of gear

ratios, often called "speeds".

The type of gearbox used in this project is a manual Nissan car gearbox. The main

specification of the gear box we selected consists of main shaft, counter shaft, and

housing. Gears are placed in the main shaft and counter shaft to transmit the

motion, whereas bearings to hold and support the shafts inside the housing. The

selected gearbox has specifications of helical and spur gearings. Gearbox

importance appears in transmitting the work output from the pistons to the car

wheels. Owing to the gear ratios, gears such as reverse gear, low gear, second gear,

high gear, & overdrive rotate in different rotational speeds. For example in high gear,

the gear ratio is 1 to 1, thus the output shaft turns at the same speed as the

crankshaft.

The objective of this project is to illustrate how a gearbox works and show the

function of each component inside it.

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3.0 Design Calculations and Drawings |

The following table shows the gearbox components and their specifications:

Part List

Item Part Name Quantity Calculations Picture Material

1 Clutch Shaft 1

C.I.

2 1st speed synchronizer

assembly 1

Steel

3 1st synchronizer hub 1

Steel

11

4 2nd gear 1

= 33

= 75

= 0.44

= 7.14

= 2.27

= 2.630

Steel

5 3rd gear 1

= 28

= 105

= 0.2667

= 11.78

= 3.750

= 4.338

Steel

6 1st gear 1

= 36

= 120

= 0.30

= 10.47

= 3.33

= 3.857

Steel

7 4th gear 1

= 16

= 70

= 0.229

= 13.74

= 4.367

= 5.05

Steel

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8 2nd & 3rd synchronizer

hub 1

Steel

9 Reverse Idler 3

C.I.

10 Countershaft 1

C.I.

11 Countershaft gear 1

Steel

13

12 2nd gear & 3rd gear input 1

Steel

13 Reverse gear 1

Steel

14 Bearing 5

Steel

14

15 Drive gear 3

Steel

16 Housing 1

C.I

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4.0 Gearbox Operation |

The gearbox principle is based on receiving the motion from the piston,

where the clutch controls whether to connect the motion to the clutch gear or not,

and pass it through the main shaft. Within the main shaft, the arrangement of the

gears decides the passage of the motion, thus, leading to specific speed of the drive

gear. In our gearbox, 5 transmissions were found and explained as follows:

4.1 First Gear: the clutch connects the motion to the clutch gear then to the

counter shaft which provides the motion to the 1st gear input. Next, the

1st gear input causes the 1st gear to rotate and thus leading to rotate the

drive shaft. The 1st gear diameter is 30 mm which is relatively large.

Though the large gear gives low speed, very large power is obtained. In

the first gear, the gear ratio is 3 to 1.

(

=

36

12=

3

1)

Figure 5: First Gear

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4.2 Second Gear: again when the clutch connects the motion to the clutch gear,

the counter shaft is directed to transmit the motion to the 2nd gear input,

hence the 2nd gear rotates leading to the drive shaft to rotate with 2.4 to 1

gear ratio; (33

14=

2.4

1). The 2nd gear diameter is 25 mm, less power but higher

speed is provided compared to the 1st gear.

Figure 6: Second Gear

17

4.3 Third Gear: as dog clutch clutches the 3rd gear of 20 mm in diameter, the

motion passes through the counter shaft leading to the drive shaft to gear

ratio of 1.4 to 1; (28

20=

1.4

1). Compared to 2nd gear, the drive shaft rotates in

very high speed with lower power.

Figure 7: Third Gear

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4.4 Fourth Gear: Owing to the straight pass of motion, the gear ratio of the 4th

gear becomes 1 to 1; the driven gear is the same as the driving gear.

Figure 8 Fourth Gear

4.5 Reverse Gear: Though, the motion of the reverse gear is similar to the first

gear, the motion of delivered to the drive shaft is in the opposite direction.

This happens due to the reverse idler which exists between the main shaft

and the countershaft.

Figure 1 Reverse Gear

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5.0 Comments and Conclusion |

Unfortunately, many difficulties were met in the project from the beginning

of how to choose a gearbox till the end of how to assemble the parts again after

disassembling. Some of these difficulties are listed below:

A gearbox was bought and disassembled and then it was discovered that the

gearbox was automatic and it had to be left and another one had to be

brought instead. 3 weeks were lost for this problem.

During disassembling the new gearbox, as we had no experience in such

thing, little help was asked. However, wrong instructions were given by the

technicians. On the other hand, one student from another group helped us

and we got back on the right track. 2 weeks were spent for disassembling.

Press machine (Appendix 1) was used to dislocate the case out of the main

shaft.

For future improvements for the following batch that they should stick to the

schedule so that they dont run out of time.

Finally, the objective of the project is successfully accomplished; the gearbox

functionality is known and the role of each component inside it is fully

understandable.

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6.0 Appendix |

This figure shows the stress machine used to dislocate the case out of the shaft:

Figure 9 Stress machine

7.0 References |

[1] Lahue, K. C., Petersen's big book of auto repair, In-text: (Lahue, 1976.)

[2] Autoweb.com, Leading Transmission Maker Predicts Major Shift to

Automatics in Heavy Vehicles, Accessed 27 May 2014.

[3] Brain, M., HowStuffWorks "How Sequential Gearboxes Work", In-

text: (Brain, 2014), Bibliography: Brain, M, and Accessed 27 May 2014.

8.0 Acknowledgment |

The student who helped us in the workshop is Muslim Abdulkayoum Saed 20124138