Speed Reduction Gear Box Design PDF

International Journal of Computer & Organization Trends – Volume 2 Issue 4 Number 1 – Jul 2012

DESIGN OF AN A SIX SPEED GEARBOX Mr. RAGURAM.R Department of Mechanical Engineering, Bharath institute of science and technology, Bharath University, Chennai-600073,Tamilnadu

ABSTRACT

ABSTRACT A Gearbox is a mechanical device that is used to provide Speed and Torque conversions from a rotating power source to output shaft. As the speed of the shaft increases, the torque transmitted decreases and vice versa. Multi-speed gearboxes are used in applications which require frequent changes to the speed/torque at the output shaft. Gearboxes work on the principle of meshing of teeth, which result in the transmission of motion and power from the input source to the output.

A gearbox is formed by mounting different gears in appropriate speed ratios to obtain the desired variations in speed. Gearboxes usually have multiple sets of gears that are placed appropriately to obtain different speed reductions. The types of gearboxes are Sliding mesh gearbox, Constant mesh gearbox, synchromesh gearbox. In a sliding mesh gearbox, the two types of gears are sliding gears and stationary gears. The sliding gears are mounted on splined shafts to enable them to slide along the axis of the shaft to enable meshing with different pairs of gear

GENERAL CONCEPT OF A GEARBOX The main purpose of a gearbox is to transmit power according to variable needs from an input power source to the desired output member. A Gearbox is a mechanical device that is used to provide Speed and Torque conversions from a rotating power source to output shaft. As the speed of the shaft increases, the torque transmitted decreases and vice versa. Multi-speed gearboxes are used in applications which require frequent changes to the speed/torque at the output shaft. Gearboxes work on the principle of meshing of teeth, which result in the transmission of motion and power from the input source to the output.

ISSN: 2249-2593

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USES OF A GEARBOX: Gearboxes are used for some or all of the following purposes, 

Changing the Direction through which the power is transmitted.



Changing the amount of force or torque that is transmitted.



Changing the Revolutionary speed of the input relative to the output.

LIST OF COMPONENTS USED IN A GEARBOX: Some of the primary components used in a Gearbox are listed below. 

Gears



Bearings



Shafts

TYPES OF GEARING The following are the primary types of gearing in a Gearbox. These may be used individually or in unison with other types.  Spur Gearing  Helical Gearing  Herringbone Gearing  Epicyclic or Planetary Gearing.

TERMS ASSOCIATED WITH A GEARBOX The following are some of the terms associated with gearboxes and their working.  Gear Ratio  Power Transmitted  Type of Drive  Step Ratio  Number of Speeds

1.4.1 GEAR RATIO The Gear ratio is the ratio with which the speed varies from one gear pair to another. In a multi stage gearbox the product of the gear ratios of each stage gives the final gear ratio. 1.4.2 POWER TRANSMITTED Power transmitted is the total power transmitted by the gearbox through its gears from the input shaft to the output shaft taking into account the losses due to efficiency and other factors. Generally the power transmitted at the output shaft is lower than the power received at the input shaft. 1.4.3 TYPE OF DRIVE This is used to denote the type of gearing and the types of contact between the gears in a gearbox. Some types are Epicyclic Drive, Synchromesh Drive, etc.

OVERVIEW AND PRINCIPLES OF COMPONENTS USED

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GEARS Gears are used to transmit power between shafts rotating at different speeds. Gears are widely used in applications which require high load carrying capacity, high efficiency and no slip between the meshing shafts.

SPUR GEARS Spur gears are gears which have vertical upright teeth perpendicular to the radial axis of the Gear wheel. The following figure illustrates the terms and notations associated with a spur gear.

FIGURE - 1

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FIGURE 2 Spur Gears are used to transmit power and motion between parallel axes or shafts. The gear types available for spur gear vary in terms of their module, metric gears, pinion gears, racks, internal and cluster gears etc. The Gears mesh or mate with teeth of very specific geometry. If the teeth are not cut to the required level of accuracy, the teeth may interfere with each other’s movements and cause jamming or locking. SOME TERMS ASSOCIATED WITH SPUR GEARS 

MODULE Module is the ratio of pitch circle diameter in mm to the number of teeth in the same gear.

 PITCH Pitch is a measure of the tooth spacing and is expressed in several ways. 1.

Circular Pitch pc : It is a direct measure of the distance from one tooth center to the adjacent tooth center. It is one of the most widely used terms in gearing.

2.

Diameter Pitch pd : The ratio of number of teeth to the pitch circle diameter in inches is called the diameter pitch.

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International Journal of Computer & Organization Trends – Volume 2 Issue 4 Number 1 – Jul 2012 

PRESSURE ANGLE

The

angle

between the line of force between meshing teeth and the tangent to the pitch circle at the point of mesh is the pressure angle. Gears must have the same module and pressure angle to mesh without interference. 2.2 BEARINGS Bearings as the name suggests are components that are used to carry load and at the same time permit constrained relative motion of the loading member. There are a number of types of bearings. Some of them are listed below. 

Roller Bearings



Ball Bearings 2.1.1 BALL BEARINGS Ball bearings are used to provide smooth, low friction motion in rotary applications. Ball bearings include

Radial ball bearings (Deep Groove and Angular Contact) and thrust ball bearings. Radial ball bearings are designed to carry both radial and axial loads, while thrust bearings are for axial loads only. Radial or Deep Groove Ball Bearings consist of an inner ring, an outer ring, balls and sometimes a cage to contain and separate the balls. These bearings are designed to permit rotational motion of one ring relative to other but do not allow axial movement. These bearings in order to function properly are assembled with a thrust load (Pre loaded). Similar applications are used for roller bearings, where in place of a ball, rollers are used.

FIGURE - 3 SHAFT Shafts are the members of the gearbox that transmit the rotary motion of the gears to subsequent stages and also transmit power from one stage to the other. They are also the members on which the gears are mounted .The shafts are coupled to the bearings to enable the shafts to rotate without much friction. In a gearbox, two types of shafts are primarily used, keyed shafts and Splined shafts. 

KEYED SHAFT

They are the shafts in which a keyway is machined so as to enable a gear to be mounted to the said shaft rigidly with the help of a key. In the case of such shafts the gears are rigidly coupled with the shaft and cannot move relative to the shaft. 

SPLINED SHAFT

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These are the shafts in which splines are cut to enable the gears which have an opposite mating spline cut into them to transmit rotational motion from the gear through the shaft without causing slip. The splines are cut to enable the axial movement of sliding of the gears on the shaft while executing rotational motion without slip.

FIGURE – 4

PROPERTIES OF SHAFT MATERIALS  Should have high strength.  Should have good machinability.  Should have great heat treatment properties.  Should have high wear resistant properties.  The material used for ordinary shaft is carbon steel of grades 40C8, 45C8, 50C4 and 50C12.  (In this design we have selected the shafts of mild steel and we have kept the key way and spline for the required dimension.)

DESIGN AND ASSOCIATED CALCULATIONS

There are many ways of approaching the design of a multi speed gearbox. One of the methods id to consider each pair individually and design them accordingly and check if they meet the required design and operating criteria. This method of design is called the Lewis Buckingham method and the gears subjected to the highest loads/stresses/forces are designed since all the remaining gears, designed proportionally will satisfy the required safe operation criterion.

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International Journal of Computer & Organization Trends – Volume 2 Issue 4 Number 1 – Jul 2012 

INITIAL SPECIFICATIONS FOR THE GEARBOX

Power transmitted

:

2KW

Max. Speed

:

1400 rpm

Min. Speed

:

460 rpm



CALCULATION OF PROGRESSION RATIO

nmax / nmin = 1400/460 = Ø6-1 Ø = 1.249 We take 1.12 * 1.12 = 1.254 (Skipping one Speed)



KINEMATIC ARRANGEMENT

Structural Formula = 3(1) 2(3) FIGURE - 5 

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RAY DIAGRAM


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FIGURE – 6 

CALCULATION OF NUMBER OF TEETH

STAGE 2 Considering the Ray that gives maximum reduction, speed is reduced from 1400 RPM to 450 RPM. Assume Z9 = 22 (Driver) (Z9 > 17) Z9 / Z10 = N10 / N9 = 450 / 1400 = 22 / Z10 = 68.44 Z10 = 69 Input speed is from shaft from gear 7 Z7 / Z8 = N8 / N7 = 1400 / 1400 The centre distances have to be same for both the pair of gears. Therefore, Z7 + Z8 = Z9 + Z10 = 22 + 69 = 91 From the above equation we get Z7 = Z8 = 91 / 2 = 45.5 = 46

STAGE 1 The sliding box consists of 3 gears. In this block, the number of teeth on adjacent gears must differ by at least 4 in order to avoid interference of gears of one shaft with the gear of the other shaft while shifting. (Z3 -Z5) > 4; (Z3 – Z1) > 4 Maximum Reduction of 1400 RPM to 900 RPM corresponds to gear 5 & 6 Z5 / Z6 = N6 / N5 = 900 / 1400 Assume, Z5 = 24; Z6 = 37

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Consider the next Ray speed reduction is from 1400 RPM to 1120RPM, corresponding to Gears 1 & 2. (Z1 / Z2) = N2 / N1 = 1120 / 1400 Z2 = 34; Z1 = 27 The next ray speed is constant at 1400 RPM through gears 3 & 4. Z3 / Z4 = N4 / N3 = 1400 / 1400 Z3 = Z4 = 31 Also, Z3 – Z5 = 31 – 24 = 7 Z3 – Z1 = 31 – 27 = 4 Since the difference in the number of teeth in the adjacent gears is greater than 4 the obtained number of teeth can be used as it is. 

Material Selection : 40 Ni2 Cr1 Mo2



MODULE CALCULATION

Equate Ft and FDB Ft = (KW * 1000 * K0)*V Where, V = Pitch line velocity in m/s K0 = Service Factor =1 Ft = (2 * 1000 * 1) / 0.5183m = 3858.76 / m FDB = σb Cv * πmby = 350 * 0.375 * π * m * 10m * 0.330 = 1360.70m2 3858.76 / m = 1360.7m2 m = 1.41 m = 1.5 (Standard) 

Calculation of b

b = 10 * 1.5 = 15mm 

Calculation of Centre Distance

a1 = (Z5 + Z6) m / 2

a2 = (Z9 + Z10) m / 2

a1 = 45.75mm 

a2= 68.25mm

Calculation of Length of Shaft

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L = 30 +10 + 4b + 20 + 7b + 10 + 30 L = 265mm 

Spindle Design

Assuming the gear is centrally placed, so that higher bending moment is obtained for safer design. α = 20 Fn = (3858.76 / m) / cos 20 Fn = 2737.60 N Bending moment due to Fn = Ft * L / 4 = 181366.29 Nmm Te = √ (BM + T ) 2

2

= 186.265 * 103 Nmm (16Te/ πds3) = 55 ds = 25mm 

Splined shaft connection since the diameter =25mm Standard four tooth Spline is chosen T= pArm

A= h*l*N

42441.3 = pArm, no .of. Splines N= 4 

Selection of Bearing

Series 6305, Deep Groove Ball Bearing is used as it meets the requirements for the loading capacity and service life.

RESULTS AND DISCUSSIONS

We have made an attempt to Design and Fabricate a Six Speed Gearbox for Low Power applications. In this process we have designed Spur Gears, Shafts, Splines, and Bearings. The Gears, Shafts were fabricated while the Bearings were purchased. 

CONCLUSION

Thus we conclude that the Gearbox designed by us is satisfactory and meets the requirements specified at the outset of the project. We would also like to state that this project can be further improved by further study research and Design.

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REFERENCES 1. PRABHU T J “Design of Transmission Elements” 2008. 2. Shigley “Mechanical Engineering Design” Tata McGraw Hill, 2004. 3. Maitra “Handbook of Gear Design” Tata McGraw Hill, 1995. 4. Hajra Chowdary S K “The Fundamentals of Workshop technology Vol I & II” Media Publishers, 1997. 5. Design Data, PSG College of Technology, 2007.

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Speed Reduction Gear Box Design PDF

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