Manual Transmission project report (Gear-box)

University of Bahrain College of Engineering Department of Mechanical Engineering Junior Project (MENG 290)

Gear Box Transmission Fundamentals

Bashar Al-Tobul Hammam Mohamed Mahmoud Islam Elghoneimy Salaar Shakeel

20125667 20123973 20124754 20122385

Semester II 2013/2014 Course Instructor: Dr. Noaman Bekheet May 23, 2014

Table of Content | Abstract…………………………………………………………………………………………………………………….3 Introduction………………………………………………………………………………………………………..…4-9 Design Calculations and Drawings……………………………………………………………….……….9-14 Gearbox Operation…………………………………………………………………………………………….15-18 Comments and Conclusions…………………………………………………………………………………….19 Appendix…………………………………………………………………………………………………………………20 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 Gear………………………………………………………………………………………………16 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

Figure 1: Spur gears

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

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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

Figure 2: 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.

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

Bevel Gear

Figure 3: 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 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 8

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

1

Clutch Shaft

1

C.I.

2

1st speed synchronizer assembly

1

Steel

3

1st synchronizer hub

1

Steel

10

Material

4

5

6

7

2nd gear

3rd gear

1st gear

4th gear

1

1

1

1

𝑁 = 33 𝑑𝑝 = 75 𝑚𝑚 𝑃𝑑 = 0.44 𝑚𝑚 𝑃𝑐 = 7.14 𝑚𝑚 𝑎 = 2.27 𝑚𝑚 𝑏 = 2.630 𝑚𝑚

Steel

𝑁 = 28 𝑑𝑝 = 105 𝑚𝑚 𝑃𝑑 = 0.2667 𝑚𝑚 𝑃𝑐 = 11.78 𝑚𝑚 𝑎 = 3.750 𝑚𝑚 𝑏 = 4.338 𝑚𝑚

Steel

𝑁 = 36 𝑑𝑝 = 120 𝑚𝑚 𝑃𝑑 = 0.30 𝑚𝑚 𝑃𝑐 = 10.47 𝑚𝑚 𝑎 = 3.33 𝑚𝑚 𝑏 = 3.857 𝑚𝑚

Steel

𝑁 = 16 𝑑𝑝 = 70 𝑚𝑚 𝑃𝑑 = 0.229 𝑚𝑚 𝑃𝑐 = 13.74 𝑚𝑚 𝑎 = 4.367 𝑚𝑚 𝑏 = 5.05 𝑚𝑚

Steel

11

8

2nd & 3rd synchronizer hub

1

Steel

9

Reverse Idler

3

C.I.

10

Countershaft

1

C.I.

11

Countershaft gear

1

Steel

12

12

2nd gear & 3rd gear input

1

Steel

13

Reverse gear

1

Steel

14

Bearing

5

Steel

13

15

Drive gear

3

Steel

16

Housing

1

C.I

14

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. 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑓 𝑑𝑟𝑖𝑣𝑒𝑛 𝑔𝑒𝑎𝑟

36

3

(𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑓 𝑑𝑟𝑖𝑣𝑖𝑛𝑔 𝑔𝑒𝑎𝑟 = 12 = 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 2 nd gear input, hence the 2nd gear rotates leading to the drive shaft to rotate with 2.4 to 1 33

gear ratio; (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

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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 28

ratio of 1.4 to 1; (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 4 th 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 don’t 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", Intext: (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

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