21-11-2012, 01:35 PM
GEAR BOX
gear box.pptx (Size: 1.2 MB / Downloads: 44)
On a conventional rear-drive transmission, there are three basic shafts; the input, the
output, and the countershaft. The input and output together are called the main shaft, since they
are joined inside the transmission so they appear to be a single shaft, although they rotate totally
independently of each other. The input length of this shaft is much shorter than the output shaft.
Parallel to the main shaft is the countershaft. There are a number of gears fixed along the
countershaft, and matching gears along the output shaft, although these are not fixed, and rotate
independently of the output shaft. A front-drive transmission is basically the same, but may be simplified. There often are
two shafts, the input and the output, but depending on the direction of rotation of the engine.
FIRST GEAR:
Let us now understand how four different speeds could be obtained from the set of eight
different gears. Meshing of 1st gear with 3rd and 5th gear with 7th gear will give the first gear
shift. This gear shift will give the maximum torque. The arrangement is shown in figure.
THIRD GEAR:
Now meshing of 1st gear with 3rd and 6th gear with 8th will give the third gear shift. The
obtain value of speed will be higher than that produced by first and second gear shift while the
torque obtained will be comparatively less. The arrangement of the third gear shift is as shown
Below
SECOND GEAR:
Meshing of 2nd gear with 4th and 5th gear with 7th will give second gear shift. The speed
achieved will be higher than the previous gear shift whereas the torque will be comparatively
less. This arrangement is as shown below.
NEUTRAL:
The gearbox will be in the neutral position if none of the gears are meshing. In the
neutral position no power is being transmitted and all the gears will be rotating ideally. The
arrangement of neutral gear shift is as shown below.
SLIDING-MESH GEARBOX:
The sliding gearbox was popular on cars up to about 1930, but it is rarely used. The basic layout of a 4-speed and reverse gearbox is shown in the figure. The various spur-type gears are mounted on three shafts. o Primary shaft (alternative names – clutch or first motion shaft) o Layshaft (countershaft) o Mainshaft (third motion shaft).