GEAR BOX IN VEHICLES

Gearbox is a device which converts speed and torque, whereas a transmission is a type of gearbox that can be “shifted” to dynamically change the speed:torque ratio, such as in a vehicle. The gearbox that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device. The most common use is in motor vehicles, where the transmission adapts the output of the internal combustion engine to the drive wheels. Such engines need to operate at a relatively high rotational speed, which is inappropriate for starting, stopping, and slower travel. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process. Transmissions are also used on pedal bicycles, fixed machines, and anywhere else rotational speed and torque needs to be adapted. A transmission will have multiple gear ratios (“gears”), with the ability to switch between them as speed varies. This switching may be done manually (by the operator), or automatically. Directional (forward and reverse) control may also be provided.

In motor vehicle applications, the transmission will generally be connected to the crankshaft of the engine. The output of the transmission is transmitted via driveshaft to one or more differentials, which in turn drive the wheels. While a differential may also provide gear reduction, its primary purpose is to permit the wheels at either end of an axle to rotate at different speeds.

WORKING

There are three forks controlled by three rods that are engaged by the shift lever. Looking at the shift rods from the top, they look like this in neutral, rev­erse, first and second gear. A sequential manual transmission works the same way. There is still a set of gear selector forks that move collars that engage gears. The only difference is the way the control rods are manipulated. The “H” pattern is eliminated and replaced with a different motion. Manual transmission come in two basic types.A simple but rugged sliding-mesh or unsynchronized or non-synchronous system, where straight-cut spur gear sets are spinning freely, and must be synchronized by the operator matching engine revs to road speed, to avoid noisy and damaging “gear clash”  and the now common constant-mesh gearboxes which can include non-synchronised, or synchronized or synchromesh systems, where diagonal cut helical gear sets are constantly “meshed” together, and a dog clutch is used for changing gears. On synchromesh boxes, friction cones or “synchro-rings” are used in addition to the  clutch.

The engine drives the input shaft as per any car.  The gears transfer the torque to the output shaft.  This shaft has a pinion on it which drives the ring gear around the diff assembly.  These two parts determine the final drive ratio of the vehicle,  and as it is before the diff they can be changed independent of any other ratio.The ring gear is around the centre diff.  This diff splits the torque between front and rear axle.  Think of it purely as a normal diff,  with two output shafts for now.  One of these shafts goes to the front diff,  which acts in the normal matter to split torque between the front two wheels.

Motions are doing is rotating a ratcheting drum.If the drum is located away from the transmission’s gears, the grooves control standard control rods. If the drum is located next to the gears, the grooves directly move the gear selector fork, and no control rods are needed. This seems to be the more common technique because it has fewer parts and is more compact. when you move the lever, it rotates the drum one increment (for example, 50 degrees). This rotation causes the rods or forks to move according to the grooves in the drum, changing the gears. Because of the drum, you have to shift in sequence. There is no skipping, for example, from first gear to third. You must always go through second gear to get to third gear. It is the same when downshifting. The advantage of this system is that shifting mistakes are impossible.

Advantages

• The sequential shift is quicker. For example, to go from 2nd to 3rd gear on the “H” pattern, you have to push the lever up, over and up again. That takes time. On a sequential gearbox, you simply push the lever up for every gear change.

• The sequential shift is consistent. You do not have to think, “Let’s see, I’m in second gear so I have to go up-over-up to get to third.” You simply push the lever forward — it’s the same motion for every gear.

• The hand location is consistent. With the “H” pattern, the location of the shift lever changes, so you have to think about where to put your hand depending on which gear you are in. With a sequential gearbox, the shift lever is always in the same place for the next shift.

• The sequential shift has no surprises. If you mis-shift with the “H” pattern in a race (for example, down-shifting to 2nd when you meant to go to 4th), it is possible to blow up the engine. That can never happen with a sequential gearbox.