Question

Write a detailed research report on GEARBOXES

Answer 1

GEAR BOX AND NECCESSITY OF GEAR BOX IN AUTOMOBILE

At the timing of starting, hill climbing, accelerating and pulling a load, we need high torque which is provided by gear box.

the gear box is necessary in the transmission system to maintain engine speed at the most economical value under all conditions of vehicle movement.

a gear box provides a wide range of different gear ratios so that engine speed could be kept at or near the value at which maximum power can be developed and it doesn't on the speed of the vehicle.

TYPES OF GEAR BOX AND GAER BOX TRANSMISSION

Constant Mesh gear box- in constant mesh gear box, all the gears are in constant mesh with each other.

these gear rotate on splined bushes independent of the output shaft.

to obtain a perticular gear ratio the output gear is locked on the output shaft by means of a dog clutch.

instead of actual gear movement, the dog clutch moves along the splined shaft by its selector fork.

Sliding mesh gear box-

Sliding mesh gear contains three parallel shafts:

a. input shaft

b. counter shaft(lay shaft)

c. output shaft.

the output and input shaft in line and counter shaft is parallel to them and lies on one side.

the engine supplies power to input shaft via clutch and input shaft transfers power to the output shaft via gears mounted on lay shaft.

the output shaft transmits power to the propeller shaft for onward transmission to road wheels.

1. Manual gear transmission- it is conventional type gear box and these are widely used on vehicles. the engagement of first, second, third and reverse gears are accomplised by the driver.

2. Semi automatic transmission.- semi automatic transmission refers to a conventional manual transmission with a automatic clutch.

3. Automatic transmission- Automatic transmission is a type of motor transmission that automatically changes the gear ratio as vehicle moves.

DESIGN OF A GEAR BOX OF AN AUTOMOBLIE

1. determine the maximum and minimum speeds of the output shafts, then calculate the number of steps or speed reduction stages for this range.

2. select the type of speed reducer or gear box based on the poer transmission requirements, gear ratio, postions of axis, space available for speed reducer.

3. determine the progression ratio which is the ratio of maximum speed and minimum speed of output shaft of gear box. the nearest progression ratio should be a standard one and is taken either from R 20 or R 40 series.

4. select materials for the gears so that gear should sustain the operating conditions and operating load.

5. determine the center distance between the driven and driver shaft based on the surface compressive stress and the module of gear by beam strength as well as fix the number of teeth required.

6. calculate the key size, shape or type of transmission keys foe each gear and select appropriate fit and tolerance for mating parts like shaft and gear.

7. select bearing types based on the loading and operating conditions. also make sure to include consideration speed and expected life of gear and gear box.

8. provide suitable clearance between gears and walls of the housing of gear box and based on the considerations the casting/ housing of gear box.

9. complete the design of casting in drawing by providing fins if necessary to have increased haet transfer by convection and conduction.

10. draw neat and clean working drawings in suitable sofware like AutoCAD, Pro engineer etc. indecating required details during manufacturing or assembly and one can also perform finite element analysis of the complete gear box after it completely designed.

GEAR RATIO AND SIGNIFICANCE OF LOW AND HIGH GEAR RATIO

it is the ratio of increse or decrease in the speed of the griven gear B with respect to the driver gear A

Gear ratio also known as velocity ratio which depends upon the number of teeth of the meshing gears, and can be expressed by

Nb/Na=Ta/Tb=speed of driven gear/ speed of driver gear

a higher gear ratio would inprove mileage and produce less wear on the engine, but at the cost of less acceleration

a low gear ratio will require a lesser amount of torque than a higher gear ratio.