Evolution Of Manual Gearbox Design

1. Using either your own data or the data provided in this brief, work out suitable gear ratios and hence gear teeth for each gear to withstand the torque requirement of: 350Nm torque.
2. Once you have completed the necessary calculations, consider the types of materials that you will use for the gear teeth. Specify benefits and disadvantages of the materials and cost drivers for the different rates of production stated overleaf and the manufacturing methods  possible.
3. Finally, model the gears and gear selectors etc. to produce a driven simulated gearbox  model. I.e. your model must be able to change gear and the output shaft change speed etc. For differentials a model showing the output direction to be accurate. You will be marked on the quality of your parts and assembly so take close care to ensure the marking scheme is read and understood before following for your design.
4. Ensure fitness for purpose for all aspects of the problem including analysis where possible, manufacturability, environmental considerations, operating conditions and maintenance.
5. Write a technical report based on tasks 1, 2, 3 and 4, include any drawing sheets in the appendix. Think of the report as a business case on why your design should be used.

The Reasoning for Manual Gearboxes

The major reasoning for having a gearbox in vehicles it to facilitate the transfer of power that comes from engines to be directed to the wheels via the driveshaft. Using various gears allows equally various torque levels that are to be directed to the vehicle wheels with a dependence to the speed that the vehicle moves changing the level of torque requires the gears being used to be shifted by automatic or manual means, this depends on the transmission type under study (Salah & Aliofkhazraei, 2015).

The manual model that was produced first came from Louis-Rene in unison with Emile Levassor. Their invention involved a transmission system that allowed transmission of three speeds in 1894. They produced the design that is the major point of starting for numerous manual transmission system. Levassor and Panhard made use of chain drives in the first transmission system. However, in the year that came afterwards, 1898 Louis Renault used the first design that was present and improved it to another level using the substitution of the driveshaft to make use of a drive chain with an addition of various axle that was applied in the rear wheels ton increase transmission in the designed manual system. This design was key as when the 20 the century began, most manufacturers of cars had to use the non-synchronized transmission that was manual that required improvement taking note of the past designed Levassor/Panhard/Renault designs. The invention that followed was the year 1928. Cadillac made use and developed a better-synchronized transmission system that was manual, with the added reduction in gear grinding and easier shifting of gears (Anon., 2016). The improvement also had smooth gear shifting. There is a studied basic gear system evolution concerning the manual gearbox. The use of helical gears is the preference that is chosen first for designing this gearbox due to the quiet and smooth operation of the gearbox in its maximum speed level. However, these types of gears are difficult to manufacture due to the increased difficulty and complexity in the time, shape, and cost of the involved individual parts (Parker, 2008)

Specifications of product’s design: the production or manufacture of these gearbox products involve the development of steps or the first development of an imagination to the engineers to be involved. These engineers would then turn the concept of these imaginations into engineering files and drawings that depict the plan of manufacturing the design. Use of PDS, therefore, would allow elimination of unnecessary delay and checklist. The communication inability to pass on an idea would make the eventual design look similar to previous designs as well as the review cycle to make the approval for the incoming step. Using the PDS procedure can be developed only if the gaolsof the design are stated clearly. In PDS, the goals involved have relations to one another, therefore, there is used for rating. Another essential step is the writing of engineering specifications (Genta & Morello, 2016).

History of Manual Gearbox Design

One appropriate way that the goal of the design can be achieved is by coming up with numerous design attributes. These attributes are then rated depending on the engineering goals with specifications guiding both designers and engineers. The end product could produce different results due to the varying inputs in design. The main purpose is to make the team of designers understand the goals of the design in the imagined process. One way of achieving this is by noting down specifications required by engineers with the help of engineering design tools such as CAD software. This software allows commencing with the initial process of production. Physical concepts can easily be used by engineers in coming up with hand sketches. The final 3D diagram could henceforth be developed by 3D CAD software that optimizes specific model parts. Better knowledge of the materials required for major purposes and the process of manufacturing that satisfies the design of required gearbox design is also facilitated by the software. Selection of material, as well as the process of manufacturing, have to sync with the requirements of the design. Use of PDS design allows various volumes of production. The needs of the customers are therefore identified early enough allowing their independence in the implementation of the final design (Gkikas, 2016)

GEAR RATIO:  this ratio has it the definition as direct measurement ratio of depicted speeds of rotation of any interlocking gears. Overall, in the start, there are two gears that include the drive gear that directly obtains more force of rotation output by the engine having the larger size than the driven gear. The last gear has a higher turn speed and it opposite the direction of the first gear. This brings out the formula;

                                    Gear ratio=T2/T1

                  T1= total teeth number of the first gear.

                  T2= total teeth number of the second gear.

Determination of the basic ratio in gears involves the use of at least two engaged gears that is the gear train. Most cases involve the first gear being the drive gear that has an attachment to motor shaft while the second gear is the driven gear that ah an attachment to the load shaft. In this project, the plan is to design a gearbox of 5-speed specification meaning there is a possibility of using many gears between the mentioned two types. These many gears would facilitate power transmission. Ideal gears are the name of the intermediate gears in between the two. Determining the gear ratio involves proper meshing that facilitates proper constant construct as one gear turns the other (Bosch, 2013). A comparison of the teeth number is another method that simpler to use in finding the gear ratio in any two gears that interlock. One more way of achieving this is by manual counting of the teeth of gears interlocking, dividing the teeth number of the driven gear by the teeth number of the drive gear, makes way for getting the gear ratio value. One important value of the ratio is the ability of the drive gear to turn one and a half times so as to make the driven gear turn once. This is because the driven gear has a bigger size than the drive gear, therefore, it will run slower. Mass has a say in this movement. The speed of the driven gear can easily be known based on the drive gear input speed (Ramanujam & Tacke, 2016).

Specifications of Product's Design

Ratio= ( Driven /Drive)* (Driven /Drive)

The following are calculations of gear ratios and formulas required for the speed designed manual gearbox.

Formulaes	(Teeth o/Teeth in)=(Dop/Dip)=(Nin/Nop)=(Top/Tip)
		Gear Ratio=G1XG2	G1=(Teeth o/p) / (Teeth i/n)	G2=(Teeth o/p) / (Teeth i/n)
	Input Torque		200 N-m
	Input RPM		5000 RPM

1st Gear-Ratio
Input Gear Ratio
G0	T o/p	34
	T i/p	31
G0	1.1
			G0XG1=4
1st Gear Teeth Ratio
G1	T o/p	50	Compound Gear Ratio=4
	T i/p	14
G1	3.6
1st Gear RPM=1250 RPM

2nd Gear-Ratio
Input Gear Ratio
G0	T o/p	34
	T i/p	31
G0	1.1
			G0XG2=2.6
2nd Gear Teeth Ratio
G2	T o/p	45	Compound Gear Ratio=2.6
	T i/p	19
G2	2.4
2nd Gear RPM=1923 RPM

3rd Gear-Ratio
Input Gear Ratio
G0	T o/p	34
	T i/p	31
G0	1.1
			G0XG3= 1.76
3rd Gear Teeth Ratio
G3	T o/p	39	Compound Gear Ratio=1.76
	T i/p	25
G3	1.6
3rd Gear RPM=2840 RPM

4th Gear-Ratio
Input Gear Ratio
G0	T o/p	34
	T i/p	31
G0	1.1
			G0XG4= 1.1
3rd Gear Teeth Ratio
G4	T o/p	32	Compound Gear Ratio=1.1
	T i/p	32
G4
3rd Gear RPM=4545 RPM

5th Gear-Ratio
Input Gear Ratio
G0	T o/p	34
	T i/p	31
G0	1.1
			G0XG5= 1
3rd Gear Teeth Ratio
G5	T o/p	31	Compound Gear Ratio=1
	T i/p	34
G5	0.911764706
5th Gear RPM=5000 RPM

Detailed calculations were done on the given geometries of gears. The major gear components in the preferred equations include; pressure angle, material strength, centre-to-centre distance, gear reduction ratio, gear teeth number and face width. Parameters need to be loaded into gear design in study making this step very important. The determination of these parameters involves coming up with the pitch-line velocity as well as determining the bending stress of every gear tooth. This has its importance in ensuring proper material selection. Materials selected have to be strong enough allowing support of stress that was calculated. Calculation of bending stress is made possible by the use of Lewis factor, max tangential and face width. Such parameters are used in calculating maximum stress. Lewis factor was produced by the use of pressure angle on gears and teeth number er gear. Talking about safety, has its numerous relations to application factor, size factor, form factor, rim thickness, load distribution and dynamic factor (Zurschmeide, 2016).

M  =  PITCH DIAMETER/NUMBER OF TEETH (Zurschmeide, 2016)

BENDING STRESS = K*W/M*B*Y (Zurschmeide, 2016)

Torque: transmitted force system is done using and via the machine or structural member, with the capability of developing efficient rotational displacement about the axis longitude.

Output Torque= Torque input/Gear Ratio (Zurschmeide, 2016).

In the above equation, the torque input equals torque output. The torque input is put on an assumption.

ENVIRONMENT AND SAFETY: one the design was completed for all of its components, an analysis of safety is to be performed. This analysis makes sure the design is safe and secure with importance focused on safety in assembling. Unfortunately, a well-assembled design of gearbox has its safety risk that come from slight improper synchronisation. The risk involved in this stage was improved to a degree that had better clarity before activation of the performance of the shaft. Any concerns about the environment are the addressed. This possible to be analysed by critically investigating the material used in making the used gears. Special care has to be taken when selecting the materials of the gear. Alloys of aluminium were considered to be detrimental to the environment if compared to cast iron or steel. Effects to the environment usually come to view when aluminium is being processed (Adler, 2007). Placement of products for mass development makes this consideration be looked at larger scales. Every country has its requirements in conserving the environment. Choosing greater toxic materials would lead to equally greater pollution of the environment. Such choices would mean increased cost of running the vehicle gearbox design. Wholly, the discussion of some material parts in mass production has its importance in consideration of various options allowing better designing of these gearboxes (Ebsch, 2010).

Gear Ratio

Design of gearboxes in this study has its focus on using numerous options of materials. To begin with, the majorly looked at components are the metals that have great endurance in sustainability, durability and loading parameters. Since the is the use of gears and shafts in this required project in having high resistance to wear, the sued gears were of steel (Corpor, 2016). The shaft selected material was an alloy due to the included bending loads. Material that was selected had to be hardened with high tear and wear resistance. Another feature is the use of an-susceptible deformability in the action of performance torsion as well as various bending cycles. In the section of gear hubs, the material that seemed ideal was to be of lower density than steel so as o reduce the weight of the gearbox in total. An alloy of aluminium seemed the chosen option due to the future of enduring stress. Such an alloy would also avail the needed elasticity modulus required in press-fit hubs. A negative effect is a constant stress due to the spline interacting. Aluminium has the benefit of better cost-effective than other components possessing features. Taking note of numerous analysis, an alloy of steel was produced to make the gears while the shift was made of aluminium alloy. Hence, the manufacturing process involved analysis of gears and shafts. The shaft calculations were therefore begun (Smith, 2016). The conventional method of machining seemed to be the better choice in shaft making. Torque to be transferred had to be included for the conduction of an analysis of bending stresses. The force and direction were determined on the analysed shaft. An assumption was made that all of the forces that were involved had horizontal alignment. The sheer force was calculated across the shaft from left to right. Shear forces obtained as well as the distance every force is located from static ends allowed calculation of bending moments (Ebsch, 2010).

Disadvantages and advantages of each part’s chosen material assembled

Part	Material	Advantage	Disadvantage
hubs	Aluminium	-easy grounding for spline creation -Already available	-Expensive - Heavy
shaft	Aluminium	-greater spline shear strength(above -Lightweight	-Expensive
Gears	Alloy Steel	-Higher shear strength for splines -Lightweight	-requires hardening
Gearbox	Aluminium	-strong, lightweight	-Expensive

The gearbox price has a variation due to the influence of accuracy, size, backlash, specification, specific manufacturer and gear ratio. Gearboxes that have backlash ranging to 30-arc minutes would cost about 50 pounds rice. If the gearbox has its value below 5-arc minutes then the backlash costs more than any gearbox possessing the high value of backlash (Couto, et al., 2017). However, the assembly costing is about 150 dollars as shown in figure 1 that appear to be impractical and wrong. This is according to the analysis that costly have their chosen materials to be an aluminium alloy or steel alloy. These materials are very expensive. In addition, alloys of aluminium have greater difficulty in manufacturing with higher toxicity to the environment when given a comparison to steel (Hobbacher, 2015).

Environment and Safety

Prototype: the objective of creating a prototype is to have a demonstration of function and form. The project allowed determination of gear sizing. Use of CAD software allowed calculation without details of the gear tooth. However, during the placement of dimensions on the CAD software, there was a realization that the beginning stages of intermediate gears were too big having gone through the shaft's output. This would fail for a practical design. Therefore, there was the reason to try the feasible reduction of gears. Error correction of the output shaft, as well as the intermediate gears, made an almost CAD model completion but few errors still remained since the time was insufficient. The use of CNC router produced the cut design from the tooling board. The needed shapes were then created whole then the steel shafts were addressed to the gear tooling board. Creation of this design helped in the extensive analysis of the design. Prototype creation was approximately 1000 – 1500 pounds (Lehmhus, et al., 2013).

Small run: mistakes that were made from prototyping were to be eliminated to keep the design more accurate I the process of manufacturing with the small run. The small run has the importance of being the intermediate stage of production and prototyping. The reduced mistakes that come up at this stage are pushed to the last stage of production. Small run, however, ha a higher sot of production than prototyping stage since the technology used in manufacturing as well as labour is higher at this stage (Mallick, 2016).

Production: This is the last stage in designing the gearbox. There needs to be the least error at this stage since after it is the market assignment. The resulting produce hat to be fully complying with the customer requirements, regulations and satisfaction. In production, the components have to be authentic and real with the requirement of large production scale in technology and infrastructure as well as labour cost and testing (Thorpe & Thorpe, 2011).

There is a three-scale production that includes;

Small run: from 2250-22500 pounds

Prototypes: from 100-1500 pounds

Production: from 33750-112500 pounds

GEAR TEETH: Cutting of gear teeth is possible by use of vertical machining. When the gear it heat treated, there is an influence on the shape, therefore, heat treating is better done before shaping. Heat treating increases tolerance of the gear ensuring nice meshing of the teeth (Menon & Malik, 2016).

GEAR HUBS: Output and intermediate gears can be removed to remain with the teeth ring. The proper tolerance level is key to press fit having the aluminium hubs. This hub of aluminium transfer enough torque. The hubs had to be turned down using the lathe and machined with CNC mill. The resulting teeth were put in the oven, as the hubs had to be dropped into dry ice mixed with acetone. The resulting gear teeth and aluminium hubs are later pressed together for large intermediate gear as well as the output gear (Tiwari & Herstatt, 2013).

SHAFTS:  in manufacturing the shaft section, polygon and spline motion had to be transferred from the rotating shaft to the end gears (Streitz & Markopoulos, 2016).

BEARINGS: Mostly, the gear bearings have to be compact, durable, reliable, offering high ratings of load to the required design. The design together with manufacture factors for proper bearing techniques is the reduced noise property the method of proper straightforward and safety requirement in the bearing mounting. Manufacturing the to meet the applications intended involves regarding the availability of space, the speed of performance, stress being loaded, operating environment and considerations to requirements of lubrication. When the bearing is mounted correctly, here is an increased performance to optimum. The latest software can be used to develop the function simulation for any bearing system proposal. BEARINX is one of this software that calculates and analyse results for engineering applications. This software only seems very important when there is a complex system being designed. For increased accuracy and speed, they are applicable. Fast modelling for bearing designs are possible with consideration of critical factors such as deformation and elasticity. In the application requiring high speed, roller bearings that are cylindrical are prepared with an external guidance disc cage made of brass. Such bearings are possible to endure great running speeds but at low frictional torque. Different bearing that may be applicable in other gearboxes is plastic bearings, polymer bearings and metal bearings (Juvinall & Marshek, 2017).

Designing the gears was performed with the use of solid works. The normal steps of designing that included drawing the circle to the intended diameter and later extrusion to the possible thickness required was done. Centre line of appropriate thickness is drawn from the gear centre to the top. Tooth profile was determined are then added to the helical gears. The gears are rotated to the other side with the teeth drawn to match the drawn ones. One tooth profile is rotated 10 degrees before using the loft base in joining the profiles designed. With a circular pattern of equal spacing, teeth are created around the gear (Silva, et al., 2016).

Conclusion:

This study produces a manual 5-speed gearbox that has a design to possess helical gears but did not function as was intended due to a failure of parts not having proper mating. In addition, the process of manufacturing which was chosen for aluminium alloy in shaft designing was cumbersome to produce. The same aluminium alloy had higher toxicity to the environment. More analysis of the design procedure showed an indication of high difficulty in manufacturing and assembly cost for the parts were however low. The main aim of the study was to come up with a design that has fully understood the working of the gearbox. Using helical gears in this study proved to be advantageous due to the capability to run smoothly at higher speed.

A brief recommendation for the above project is an increase in the shaft and gear designing for more compactness with an added analysis, design process and material selection. It is also a good recommendation to obtain the initial ratios of gears before beginning the meshing. Lastly, it is good to make us of recent types of bearing such as plastics.

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