Where is gearbox

There are many terms that gear manufacturers as well as engineers and designers use to talk about what sometimes is essentially the same thing. The most basic definition of a gearbox is that it is a contained gear train, or a mechanical unit or component consisting of a series of integrated gears within a housing. In fact, the name itself defines what it is — a box containing gears. In the most basic sense, a gearbox functions like any system of gears; it alters torque and speed between a driving device like a motor and a load.

The gears inside of a gearbox can be any one of a number of types from bevel gears and spiral bevel gears to wormgears and others such as planetary gears. The gears are mounted on shafts, which are supported by and rotate via rolling element bearings. The selector rods lie parallel with shafts carrying the gears. The most popular design is the constant-mesh gearbox. It has three shafts: the input shaft , the layshaft and the mainshaft, which run in bearings in the gearbox casing.

The engine drives the input shaft, which drives the layshaft. The layshaft rotates the gears on the mainshaft, but these rotate freely until they are locked by means of the synchromesh device, which is splined to the shaft.

It is the synchromesh device which is actually operated by the driver, through a selector rod with a fork on it which moves the synchromesh to engage the gear. The baulk ring, a delaying device in the synchromesh, is the final refinement in the modern gearbox.

It prevents engagement of a gear until the shaft speeds are synchronised. On some cars an additional gear, called overdrive , is fitted. It is higher than top gear and so gives economic driving at cruising speeds. The synchromesh device is a ring with teeth on the inside that is mounted on a toothed hub which is splined to the shaft.

When the driver selects a gear, matching cone-shaped friction surfaces on the hub and the gear transmit drive, from the turning gear through the hub to the shaft, synchronising the speeds of the two shafts. Due to the variable nature of the vehicle resistance resulting in load and gradient changes, it require that the engine power should be available over a wide range of road speeds.

Hence, for this reason, the engine speed maintain by using a reduction gear resulting in the road wheels rotating at a proper speed suited to the operating conditions of the vehicle. Therefore, a single torque multiplication in the rear axle must be interposed and a variable multiplication factor in the gearbox is provided for this purpose.

To maintain engine speed on all conditions of load and vehicle speed, the gearbox uses a system to maintain engine speed, while sacrificing the same road speed. To enable the engine to run faster on-road wheels as well as to multiply the torque, a gearbox is required.

A clutch shaft is a shaft that takes power from the engine to supply another shaft. The clutch shaft or driving shaft is connected through the clutch and when the clutch is engaged, the driving shaft also rotates.

Only one gear is fixed on the clutch shaft and this engine rotates with the same speed as the crankshaft. In addition, the driving shaft and main shaft are in the same line. The counter shaft is a shaft that connects directly to the clutch shaft. It has gear which connects it to the clutch shaft as well as the main shaft.

It can be run at engine speed or below engine speed according to gear ratio. The main shaft or output shaft that rotates at different speeds and also provides the necessary torque to the vehicle. The output shaft is a splined shaft, so that the gear or synchronizer can be moved to engage or disengage.

The bearings are required to support the rotating part and reduce friction. The gear box has both a counter and main shaft which is supported by the bearing.

Gears are used to transmitting the power from one shaft to another shaft. The amount of torque transmitted through the gears depends on the number of teeth and the size of the gears. All gears except those on the main shaft are fixed to their respective shafts; They can slide in any of the directions along the shaft. Gear selectors are simple devices that use a lever that selects gears to engage in disengage mechanisms.

The motion of the lever slides the engaging part on the shaft. It depends on the type of gearbox whether the lever slides the gear or synchronizer that are already forged along the main shaft. It is the simplest type of gearbox. In this gearbox, spur gears are used. The Figure shows the construction of a sliding mesh type transmission having three forward and one reverse speeds.

There are three gears 1, 6 and 5 attached on the main shaft and four gears 2, 3,4 and 7 on the layshaft. The two gears on the main shaft 6 and 5 can be slided by a shafting yoke and mesh with the gears 3 and 4 on a layshaft. Therefore, it is called a sliding mesh gearbox.

A separate idler gear 8 is mounted on the idler shaft. Figure shows the construction of a constant mesh type gearbox having three forward and one reverse speeds. In this type of gearbox, all gears are constantly in mesh and dog clutches are used for engaging and disengaging the gears. The dog clutches D and D2 are mounted on the main shaft. One D2 is connected between clutch gear and reverse gear whereas the other D is placed between low speed gear and reverse gear.

The splines are provided on the main shaft for the linear movement of dogs. Dog clutch can slide on the shaft and rotate along with it. All gears are rigidly fixed on the counter shaft. All main shaft and layshaft gears, and idler gears are engaged by dog clutch to obtain opposite and slow speed. Only reverse gears are spur gear type and all others are helical gears.