Design And Fabrication of Six Speed Constant Mesh Gear Box

Design And Fabrication of Six Speed Constant Mesh Gear Box

M. Santhanakrishnan1, N. Maniselvam2

Assistant Professor, Department of Mechanical Engineering,

S.K.P Engineering College, Tiruvannamalai 606611

Abstract – All the automobile vehicles available are always set to changing speed and torque between engine and driving wheels. Torque is not directly changed but it can be done in the form of power using a suitable device. It is a very useful method that we adopt, and it is also easily affordable. Many other alternative, even though more elegant, and appear to be more effective are not feasible when it comes to transmission. This project mainly focuses on the design and fabrication of a gear box that can transmit torque to the maximum and also helps to do some useful work in automobile where power transmission is a major factor. The transmission of power is done in six speeds in this project. The setup uses two shafts and thirteen gears arranged in suitable distances to achieve the desired torque and speed.

Key words: Gear, Shaft, Dog clutch, Ball bearing, lever.

1. INTRODUCTION

   The present day world is moving towards globalization. Now to keep at par with the global market, the countries follow a different set of standards.

   The main purpose of these standards is to make a product available, in every nook and corner of the world with exactly the same specifications without any single change.

   The standards are being adopted in each and every field of technology and science. These changes, especially in automobile next to the clutch are the transmission in the transmission system of a motor vehicle. The word

   transmission is used for a device that is located between clutch and propeller shaft. The device used for the transmission is Gear Box.

2. PURPOSE OF THE GEAR BOX

   • The purpose is to provide high torque at the time of starting, accelerating and pulling load. When vehicle is starting a high torque is required at the driving wheels.

   • Hence a device must provide to permit the engine crank shaft to revolve a relatively high speed, while the wheels turn at high speeds. This is obtained by a set of gears called a transmission or gear set. The gear set is enclosed in a metal box called a Gear Box.

   • It helps to reduce the engine speed in the ratio of 4:1 in case of passenger cars and in a greater ratio in case of Lorries.

   • It helps the turning of drive around 90 and to drive driving wheels at different speed.

3. THE WORKING OF 6 SPEED CONSTANT MESH GEAR BOX

   The six speed constant mesh gear box has two shafts , one for the input and the other for output. Six gears are mounted on both the shafts and are in constant mesh. Ball bearings are connected to the gears on the output shaft which makes them to rotate freely on the output shaft.

   The output gears have extensions on one side for the engagement purpose. The clutches are engaged and disengaged with the gears by the use of levers. The clutches are keyed to the output shaft. The engine flywheel is connected to the input shaft.

   The gears on the output shaft rotate freely on the bearings. Inorder to engage the dog clutch with the gear the respective lever is moved. This moves the clutch towards the gear and the dog gets engaged with the extensions on the gear. The rotation is transferred to the output shaft. The wheels connected to the output shaft are also rotated.

4. DESIGN PROCEDURE

   4.1. DESIGN CALCULATION

   PINION

   C45 steel

   o u = 630MPa HB=215 GEAR:

   C45 steel

   o b = 210 MPa E=2.15 X 105 N/ mm2 [DATA BOOK Pg No. 8.4, 8.5, 8.14] GEAR RATIO

   i = 1.4

   NUMBER OF TEETH

   Teeth on Pinion: 38

   Teeth on Gear: 54 TANGENTIAL LOAD

   Power to be transmitted = 1.5 KW Input speed =750 rpm

   Ko =1 (steady load) Ft=(P/V) Ko Ft= [(1500)/[(m(38)(750)/60 x103]] x 1 V=[ d1N1/(60 x 103)]

   Ft = 1005.16/m V=[ mZ1N1/(60 x 103)] INITIAL DYNAMIC LOAD:

   [Cv From Data Book PgNo. 8.51] Fd= Ft xCv Assume Vm = 3 m/s

   Vm< 10m/s Fd=(1005.6/2) x 2 Cv = (3+Vm)/3 Fd=(2011.3/m) Cv=2

   BEAM STRENGTH:

   [Fs from DataBook PgNo. 8.50] s=[ b] bym [b = o/3] [b]= [(u)/3] = 210mPa
   [y-From DataBook PgNo.8.50]

   b=10m [Assumption] y=0.154 (0.912/z1) = 0.13 [Take 20 INVOLUTE]

   Fs=[ 210 x 10m x 0.13 x x m] Fs=[ 857.22 m 2]

   EVALUTE

   Fs = Fd

   857.2 m2= 2011.3/mm=1.32

   Standard Value m=1.5 mm

   [From Data Book PgNo.8.2,Standard Value]

   Face value, b =15 mm Pitch diameter, d= 57mm

   Velocity, v= 2.237 m/s

   1. RECALCULATED BEAM STRENGTH

      [Fs = From Data Book PgNo.8.50] Fs= [210 x 15 x0.13 x x 1.5] Fs=1928.47 N

      ACCURATE DYNAMIC LOAD Fd= Ft+[21V (b1Ft )]

      Ft={p/V}=670.54

      b=15mm V=2.237 m/s

      Assume Carefully Cut Gear: e=0.025

      [e- From Data Book Pg 8.53 Table 42, m upto 4]

      c=296.5

      Fd=670.54 + [(46.977(51118.04))/46.977+71.54)] Fd=2699.19 N Fd> Fs

      Design is not safe Assume precision Gear: e=0.0125

      [e- From Data Book Pg 8.53 Table 42, m up to 4]

      c=148.25

      Fd=670.54 + [(46.977(2894.29))/46.977+53.79)] Fd=2019.844 N Fd> Fs

      Design is not safe D1=57mm

      Q=2i/(1+i)=[(2 x 1.42)/2.42]=1.173

      [From Data Book PgNo.8.51]

      B=20 mm

      K=[((1)2)sin 20)/1.4] x [(1/(2.15 x 105))+ (1/(2.15 x 105))] [From Data Book PgNo.8.51] [c] = Contact compressive stress

      [Data Book PgNo.8.16]

      HCR -48[scale] [Data Book PgNo.8.38] HB 460[Case hardened] [Data Book PgNo.8.16] Kc1=1[life <10 7rpm] [Data Book PgNo.8.17 Table 17] [c]= Cr HRC Kcl

      =256 x 48 x1

      12720 kgf/cm2

      1272 N/mm2

      K=[(1272)2)sin 20)/1.4] x [(1/(2.15 x 105))+ (1/(2.15 x 105))]

      K=3.67

      Fw=57 x 1.173 x 3.67 x 20 Fw=40907.59N

      Fd= Fw

      Design is Safe Basic Dimensions:

      MODULE m=1.55mm FACE WORTH b=20mm TEETH

      Z1= 38 Z1=54 PITCH DIAMETER

      d1= 57mm d2= 81mm CENTER DISTANCE O=69mm

      TOOTH DISTANCE H= 3.375mm

   2. DESIGN PROCEDURE FOR BEARING SHAFT DIA: 10 mm

      Bearing No: SKF 6200[from DataBook PgNo.4.13]

      ISC NO: 10BCO2

      Inner Dia: 10mm

      Outer Dia: 26mm Width: 9mm

      Life required for Bearing: 1 x 107 rev Dynamic capacity C= (L/L10)(k/p)P Equivalent Load =P[XFr+YFs]S

      [L10 =1mr K=3vfor Ball Bearing from Datebook] Fr=[2Mt/D] Mt=[(P x 60)/2dN]

      Fr=[(2 x 27.13 x 10 3)/81] Mt=227.13 x 10 3 N mm

      P=Power =1.5 x W d=57mm N1=Initial Speed N1=750 rpm

      N2=75001.42 = 528 rpm Ft=670.8N=Fa

      Fr=Ft ton 20 Fr=243.81N Fa/Fr=2.75

      For bearing no:skf 6200 Co=2240N Fc/Co=(670.8/2240)=0.299

      Fc/Co=e=0.299 Fc/Fr>e

      [from databook Pg No:4.4]

      X=0.56 Y=1.1608

      S=service factor

      [databook Pg No:4.2] S=1.3[Rotary m/c with no impact] P=[0.56×243.8+1.1608×670.8]1.3

      P=1189.75 N C=(L/L10)1/kp C=(1×107/1×106)1/3×1189.75

      C=2563.23 N C=256.32 Kgf

      As dynamic load ratio for SKF6200 bearing is c=400 kgf

      The selected bearing SKF6200 is safe SKF6200

      D=10mm D=26mm

      B=9mm allowable speed=20000 rpm

   3. DESIGN OF SHAFTS: Shaft-engine shaft

   Nmin=750 rpm Mt=Px60/2 N

   =1.3x103x60/2xx750

   =19.10×103 Nmm

   Pt=2Mt/D

   =2×19.10×103/38

   =1065.7 N

   Pn=Pt/cos 20

   =1069.7

   Mb=PnL/4=1069.7×100/4 Mb=26.742×103 Nmm

   Mteq=Mb2+Mt2 Mteq=32.86×103 Nmm T=16Mt/d3 =55

   =16×32.86×103/ d3 D=14.49mm

   D=16mm NHW=529 rpm

   Mt=27.09×103 Nmm pt=[(2x 27.09×103)]

   pn=(Pt)/cos20=106.7 N

   Mb=(Pn x L)/4 =26.09 x 10 3Nmm

   Mtor= 38.031 Nmm

   T=[(16Mb)/ d3 ]

   55=[(16x 38.03 x 103)] d=15.21 mm

   D=16mm R20 Series DataBook

5. FABRICATION PROCESS

The material for shaft and gear are taken as C 45 steel. The gears and the shafts are fabricated in the following method.

Gears

Machining, drilling and boring

These operations where done in gears at centre to produce hole in the gears to hold on the shaft.

Shafts

Turning-These operations are done in lathe for the shaft in which the cylindrical objects may be produced. With the work piece rotating and single point cutting tool

Welding-This sort of operation is done to fix the gears onto the shaft.

Assembly

After machining the components, they were assembled.

• At first, the gears are mounted on the shafts as a preliminary process the two dog clutches are mounted on the shaft. One in the input shaft and another in the output shaft.

• For the rigid support of gears on the spline shaft a bearing is provided over a dog clutch.

• The bearings are fixed to the mountings on the shaft.

• The gear shift lever is fixed, in the assembly for engaging gears.

Fig. 1 CAD Model of Six speed constant mesh Gearbox

Fig. 2 CATIA Model of Six speed constant mesh Gearbox

CONCLUSION

Although there are much advancement in the field of designing and fabrication of gear boxes, the constant mesh gear box is one of the most efficient gear boxes. The Project was an exposure to the world of practical working knowledge. It gives us an opportunity to apply the theories studied in the curriculum in a practical situation. It also gave an opportunity to know the practical difficulties that arise in the process of designing and fabrication. A gear box can also be designed and fabricated for 4, 8, 12, 16, etc as per the requirement using the same principle and method.

FUTURE SCOPE OF THE PROJECT

The future scope of the project is by replacing the material of the components with a low weight and high strength materials. The dog clutch can be engaged or disengage by hydraulic or pneumatic systems with help of sensors. We can also reduce the number of gears and obtain the same number of speeds. The type of engagement between the dog clutch and the gear can also be improved by some other means.

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