what is a Gearbox and how it works?

Answer 1

Let me starts with an example:
A heavy rotary kiln is to be rotated at 1 RPM, and you have a 1440 RPM motor, then you have to think of gear box/gear reducer.Couple the shaft of a motor with with input shaft of a gearbox ,(which may be single stage, multi stage depending upon the ratio.)out put shaft of the gear box to the rotary kiln using coupling [which is capable of taking designed starting torque].

In gear box there is a meshing of gears(e.g.spur,bevel,helicle,herringbone etc.),which follows the following formula:
simple gear box:
RPM1*NO. OF TEETH OF 1ST GEAR
=RPM2*NO. OF TEETHOF 2ND GEAR.
multistage gearbox:
Nn/N1=T1/T2*T2/T3*T3/T4..........*N(n-1)/Tn,where
Nn is n th gear and
There are no. of gears depending on the speed and torque.
So, in our case,ratio of gearbox required is,
1440*t1=1*t2
t2/t1=1440
This much ratio required huge gear box which is practically
not feasible.
SO, IN such a case , we have to designed the gear box in 3 to 4 stages.
Every gear is mounted on bush bearing or rolling contact bearing which are lubricated with gear oil having different viscocity depending on the size of gears inside and ratio.

Input shaft of the gearbox is having smaller diameter and out put shaft is having bigger diameter.WHY? Think about torque!


Gearbox is the system of gears and/or the hydraulic system (called variously "hydrodynamic", "fluid" or "automatic" transmission) that transmits mechanical power from a prime mover—such as an engine or electric motor—to some form of useful output device, normally rotary in form, and generally at a reduced rate of angular speed but at a higher motive torque.
Generally, transmissions will provide a significant speed-power conversion known as gear reduction (in speed) to a higher torque (rotational force or power) through the use of gearsets. In motor vehicle transportation, a vehicle transmission may provide many different speed-power ratios known colloquially as "gears" or "speeds", and possibly several variant speeds in reverse direction as well. Tractors and large trucks especially may have a dozen or more forward "gears" which vary from a crawling speed at high torque to high speed at low torque where the only torque needed with a load coasting along at a given speed are that small additional energy (force) needed to overcome ongoing friction and other road losses such as climbing a grade. When the torque needed to surmount a grade is insufficient at a higher rotational speed, the gearbox is shifted into a lower gear to provide more power, as was needed when initially accelerating said vehicle to the desired road speed. Gearing has much in common with the mechanics and mechanical factors present in pulley systems. One trades distance (numbers of rotations) for increased force.
Gearboxes have found use in a wide variety of different—often stationary—applications.
Transmissions are also used in agricultural, industrial, construction, mining and vehicle equipment. In addition to ordinary transmission equipped with gears, such equipment makes extensive use of the hydrostatic drive and electrical adjustable-speed drives.

for cross-sectional drawing,pl. visit :
www.mech.uwa.edu.au/DANotes/gears/intro/intro.html
www2.rgu.ac.uk/celt/em/avdi/showreel/pages/gearbox.htm
metalworking.com/DropBox
sales.nordex-online.com/Fotos

Answer 2

A gearbox converts an input angular velocity and torque to an output angular velocity and torque. Like a transformer in electronics, the power in will equal the power out(minus frictional losses). So for example, if you wanted to double the speed of a shaft, connect it to the gearbox and you'll get double the speed BUT half the torque. You increased speed, but decreased torque at the same ratio. This is the purpose of a gearbox.

Answer 3

In mechanics, a transmission or gearbox is the system of gears and/or the hydraulic system (called variously "hydrodynamic", "fluid" or "automatic" transmission) that transmits mechanical power from a prime mover—such as an engine or electric motor—to some form of useful output device, normally rotary in form, and generally at a reduced rate of angular speed but at a higher motive torque.

Generally, transmissions will provide a significant speed-power conversion known as gear reduction (in speed) to a higher torque (rotational force or power) through the use of gearsets. In motor vehicle transportation, a vehicle transmission may provide many different speed-power ratios known colloquially as "gears" or "speeds", and possibly several variant speeds in reverse direction as well. Tractors and large trucks especially may have a dozen or more forward "gears" which vary from a crawling speed at high torque to high speed at low torque where the only torque needed with a load coasting along at a given speed are that small additional energy (force) needed to overcome ongoing friction and other road losses such as climbing a grade. When the torque needed to surmount a grade is insufficient at a higher rotational speed, the gearbox is shifted into a lower gear to provide more power, as was needed when initially accelerating said vehicle to the desired road speed. Gearing has much in common with the mechanics and mechanical factors present in pulley systems. One trades distance (numbers of rotations) for increased force.

Answer 4

(m)

The classic answer to "What is the Gearbox for?" is "To keep the oil in", which is fair enough unless you want to know how it works! In this series we will dip into the tool chest to see if there is anything to help us understand some of the fundamentals of the motor car's innards. After all, if we have a problem, we stand a much better chance of working out what has gone wrong, and what to do about it, if we know how the thing should work. So what, basically, is inside this particular oil can?

The following diagrams show the simplest form of sliding mesh gear box with three forward speeds and reverse, the function of which is to change the speed of the transmission shaft relative to the primary/input power shaft from the engine. Diagram 1 shows the gears in Neutral. The sliding Gear can be moved along the Splined Mainshaft by the gear Lever. The Primary shaft is in 'constant mesh' with the Lay Shaft, which has a larger gear so that it turns slower. In Neutral the layshaft turns freely and is not connected to the transmission shaft.

To engage 1st Speed, the sliding gear is moved to the rear until its larger gear meshes with the smaller,1st Speed gear on the layshaft. The connection to the transmission shaft is now through two sets of reduction gears as shown in Diagram 2, so the transmission shaft turns at its lowest speed.

To engage 2nd Speed, the sliding gear is moved forward until its smaller gear meshes with the 2nd Speed gear on the layshaft as in Diagram 3. These gears are normally the same size, so the drive path is now though only one set of reduction gears and the transmission shaft turns faster.

To engage Top Speed, the sliding gear is moved further forward until the dog clutch engages, as in Diagram 4, the drive path now being straight through to the transmission shaft, which is now driven at the same speed as the input shaft from the engine. To engage Reverse, the sliding gear is moved fully rearwards until it meshes with the reverse idler pinion as in Diagram 5, the idler having the effect of making the transmission shaft turn in the opposite direction, ie, the car will go backwards. To make room for the idler, the reverse gear was often smaller than the 1st speed gear, so the overall reverse ratio was lower than 1st speed. This is why some old cars could go up hills backwards that they couldn't climb in bottom gear going forwards!

In later gearboxes, the sliding gear was made up of two separate gears, the front gear for top and second, the rear for first and reverse, each moved by its own gear selector fork. The forks are controlled by a gate and interlock mechanism which prevents two gears being engaged at the same time. Diagram 6 shows an early type of selector and 'H' gate mechanism. A latch prevents inadvertent engagement of reverse gear.

Driving with these sliding gears requires great skill and is often very noisy, with double de-clutching being an absolute must! For Connie's benefit, double de-clutching brings the two gears to the same speed so that they can be easily and quietly slid into engagement. The sequence is:

1. Depress clutch and move gear selector to neutral. (The mainshaft gear is rotating relative to road speed.)

2. Release clutch and adjust, engine revs to bring layshaft gear to a speed appropriate to the road speed and mainshaft gear to be selected. (Higher revs when changing down, iower when changing up.)

3. Engage next gear, simultaneously depressing clutch slightly to allow slippage in case gear speeds were not fully synchronised. (Nobody said it was easy!)

For pictures goto the below link

http://www.singster.co.uk/mascot%20January-February%202003.html

Answer 5

Do you understand levers?

Consider a series of gear wheels to be a series of circular levers.