Automotive Essay: Differential, Gear Box, And Clutch Are Crucial Components.

1.1 This assignment involves the selection and layout design of suitable transmission systems to drive a new generation of diesel trains with underfloor diesel engines.  The equipment has to be selected (and the ratios of each gear pair determined, etc.) so that the train meets the required performance, ideally using the minimum of energy output (and fuel input).

1.2  Each course member will be given a different variant to design.  For each variant of the performance specification, the required station to station times and station to station distances are already specified.  The vehicle masses and passenger loads have been estimated and the average track gradient for the route is known.  The engine (power rating), vehicle maximum speed and transmission ratios (etc.) will need to be selected appropriately.
1.3  The first area of work of the assignment relates to the Automotive Type Transmission.
However, later in the assignment, alternative types of transmission are to be considered.
1.4 The assignment must be in the form of a written report (clear handwriting is sufficient) with drawings showing sketched layouts and specifications of the chosen equipment  (CAD is not necessary).   A number of graphs will be needed and these may be done by hand, or by using Excel.   Do not use CAD or word processors unnecessarily: the work must be in self-explanatory note form: long essays are not required!
1.5 Please bear in mind that the number of hours spent on this work should be approximately the same as the number of marks allocated. (30% of 20 credits: equivalent to approx. 60 hours).  
1.6 Higher marks will be given for complete work (and designs) demonstrating understanding of the subject.  No marks are allocated for “beauty” of the submission, provided the work is completely clear.

Different Types of Automotive Type Transmission Components

Automotive Type Transmission (R, et al., 2015):    

           

Differential: The differential is a device that splits the engine torque two ways, allowing each output to spin at a different speed. The differential is found on all modern cars and trucks, and also in many all-wheel-drive (full-time four-wheel-drive) vehicles. Differential helps in turning the drive wheels at different rpm while the vehicle takes a turn Differential gear, in automotive mechanics, gear arrangement that permits power from the engine to be transmitted to a pair of driving wheels, dividing the force equally between them but permitting them to follow paths of different lengths, as when turning a corner or traversing an uneven road. Wheels receive power from the engine via a drive shaft. The wheels that receive power and make the vehicle move forward are called the drive wheels. The main function of the differential gear is to allow the drive wheels to turn at different rpms while both receiving power from the engine. When a large vehicle has to curve on road, outer wheels cover more distance as compared to inner wheels, so in order that wheels do not skid, we use Differential. It consists of no. of gear wheels like Crown Wheel or Ring Gear and Tail Pinion. Tail pinion is mounted after propeller shaft. It drives Ring Gear which consists of Sun and planet gear assembly. So whatever the type of curve is, Lift or Right Turn, that respective shaft, precisely B.P. shaft, revolves faster, resulting in that wheel revolving faster. Differential can be used in Rear or Front Axle or in both, depending on Drive, 2 wheel Front or Rear Drive or Four wheel Drive.

Gear Box: The gear box is the second element of the power train in an automobile. It is used to change the speed and torque of vehicle according to variety of road and load condition. A gear box changes the engine speed into torque when climbing hills and when the vehicle required. Sometimes it is known as torque converter. Provide the torque needed to move the vehicle under a variety of road and load conditions. It does this by changing the gear ratio between the engine crankshaft and vehicle drive wheels. Gearboxes are nothing but gear trains mainly for power transmission from the power producing device to the vehicle's wheels, reducing torque increasing speed, and maintaining the speed and torque of the machine shaft and transmission shaft. The gearbox is a set of gears packed into a casing. The gears inside are of different sizes and have different number of teeth. This is because, the gearbox can then cater to the demand of varying speed and torque. Each gear has a specific speed and torque response. It is combination or a set of gears meshing each other & mounted on shafts with bearing to support them. It can be used either to reduce or increase the speed ratio of input shaft. The housing will have usually two halves bolted to each other & uses a lubricating oil filled inside to reduce heat due to friction caused by meshing of gears. This is a general concept of gear box basically to transmit power or rotation from one drive to another.

Differential

Clutch: A clutch is a mechanical device which engages and disengages power transmission especially from driving shaft to drive shaft. The principle behind working of clutches (friction) is that no torque/power gets transmitted until both the friction plates touch each other. One friction plate is bolted to flywheel & the other is movable over the crankshaft. Its function is to transmit the torque from the engine to the drivetrain, smoothly deliver the power from the engine to enable smooth vehicle movement, Perform quietly and to reduce drive-related vibration. The clutch connects the engine to the wheels and when we step on the clutch it disconnects the engine. Clutch control refers to the act of controlling the speed of a vehicle with a manual transmission by partially engaging the clutch plate, using the clutch pedal instead of (or in conjunction with) the accelerator pedal. Clutch works on the principle of friction because when the two rough surface clutch plates are comes in contact with each other then they become rotating as a single unit. In the simplest application clutches are employed in devices which have two rotating shafts. In these devices one shaft is typically attached to a motor or other power unit (the driving member) while the other shaft (the driven member) provides output power for work to be done. Some types of clutches used in vehicles are given below : (a) Friction Clutch : It may be (i) single plate clutch, (ii) multi-plate clutch, or (iii) cone clutch.

1. It pick up its load smoothly without grab or clatter
2. It damp out any vibration of the crankshaft to prevent gear clatter
3. Require little pedal pressure to operate it.
4. Easy to adjust and service
5. Be cheap to manufacture

6.2 Component Torque and Speed:

 Considering vehicle Power plant as a diesel engine

Let Efficiency of diesel engine = η_d

Input Power = Indicated Power = Brake Power + Friction Power

P_input = T_input x ω

Let velocity of Piston = 2LN = V_p

Where N= rpm

N= Speed (rpm)

N= n for 2 stroke

N= n/2 for 4 stroke

N= rpm i.e revolution of crank per min.

P_input= Indicated Power (IP)

ω= 2πn/60

Considering 2 stroke engine

N= V_p/2L

L = length of stroke

P_input = T_input x ω = Ip

T_input=  IP/ ω = Input Torque.

Let η_mech= Mechanical Efficiency of Engine

T_output= Brake Power/ω = IP X η_mech/ω (W. & P., 2004)

For Under Floor Rail engine We consider Locomotive of 4500 hp two stroke diesel engine

6.3 Layout of Locomotive:

6.4 Main Gearbox ratio selection

In diesel locomotive the gears are only used in between the traction motor & the wheal by Gear pinion arrangements

The Gear ratio the above system is

Calculating by following law of gearing concept

Gear Box

i.e ω_p/ ω_g =  T/t = Gear ratio

t= no. of teeth on driver/ gear

T = no. of teeth on driven/ pinion

Now, Power of Pinion = η_gear X Power at gear

Power at gear = η_motor   X  Electrical power

ω_p = angular speed of pinion (rad s^-1)

ω_g = angular speed of pinion (rad s^-1)

Power = Torque X angular Speed (B., et al., 2011)

6.5 Calculation of Tractive effort in each gear

Tractive effort on the Driven Wheal is given by

F_t = T_ω / r_dyn

T_ω = Torque Transferred to the driven wheals

r_dyn= Dynamic radius of the type

For Driven gear, tractive effort is given by

F_t = T_p / r_p

T_p= Torque Transferred to pinion

R_p= Dynamic radius of the Pinion

Vehicle speed can be given be

V =π N_pr_dyn / 30G

G = Gear ratio

r_dyn = Dynamic radius of Wheal

N_p = Speed of Pinion (rpm)

6.6. Calculation of acceleration:-

S=(u*t)+(0.5a*t^2)

Where,

S= distance travelled.

u= initial velocity =0

v= final velocity

t= time taken.

Therefore, acceleration a= (2*S)/(t^2)

Residual force = Mass of vehicle * Acceleration

6.7. A) Plot between Speed & distance     

        

1. B) Plot between Residual force & acceleration

6.8. The above transmission system is totally based on the assumption values. To check the practical result the practical values can be used in the expressions and the results can be evaluated.

6.9. The three fundamental drive systems are:-

1. Hydraulic drive system.
2. Manual drive system
3. Automatic drive system.

Hydraulic drive system: - Basically this system comprises of fluid coupling and the torque converter.

A fluid coupling is a hydraulic system which transmits rotating mechanical power. In other words we call it as a hydrodynamic system. It is an alternative to the mechanical clutch. The turbine is connected to the input shaft of the automobile engine.  As the speed of engine increases the torque is transferred to the input shaft by the motion of the fluid (Galal, 2009).

Fig. View of the fluid coupling.

Torque converter is also a hydraulic system which controls the torque at fluctuating engine speed. It provides a variation of low to high ratio. It generally multiplies the torque when there is difference between input and output rotational speed, We can also call it as reduction gear.

Manual drive system:- In this system driver manually selects the gear during driving. Clutch plays an important role in this system. Clutch helps in engaging and disengaging of the imput shaft with the output shaft with proper gear selection. (J., 2010)

Fig. Manual drive system.

Automatic drive system:- It is the most advanced system which reduces the mechanical efforts and obtains different speed automatically. This is also called as hydromantic system. It is provided by epicyclic gear arrangement, fluid coupling and a torque converter. The working of the fluid coupling and the torque converter is explained above.

Fig. Automatic drive system showing epicycles gear train arrangement.

Stages of automatic system are:-

1. Park (P):- By selecting the park mode the transmission gets locked thus vehicle movement is restricted.
2. Reverse(R):- By selecting reverse mode vehicle is allowed to move backwards.
3. Neutral (N):- This mode disconnects the transmission with the wheels.
4. Low (L):- This mode lowers the vehicle speed during moving on hilly and muddy areas.
5. Drive (D) This mode allows the vehicle to move and accelerate the vehicle through the gear range.

Fig. Different modes of automatic drive system.

References

B., B. H., J., R. & W., N., 2011. Fundamentals, Selection, Design and Application. 2nd ed. London: Springer Heidelberg Dordrecht.

Galal, R. M., 2009. Fluid Power Engineering. New York City: The McGraw-Hill Companies.

J., E., 2010. Automatic Transmissions & Transaxles. 5TH ed. Boston: Delmar Cengage Learning.

R, F. et al., 2015. The Automotive Transmission Book. Switzerland: Spring International Publication.

W., H. V. A. & P., C., 2004. Hillier's Fundamentals of Motor Vehicle Technology, Book 1. 5th ed. Heltenham : Ielson Thornes Ltd.