- March 3, 2018
- Posted by: maxpower
- Category: Uncategorized
Gearbox in mainly divided into two types based on the type of transmission-
- Automatic Transmission Gearbox:
A transmission in which various speeds are obtained automatically is known as an automatic transmission. An automatic transmission is generally subdivided into two types:
- Epicyclic gearbox: This type of gearbox uses no sliding dogs or gears to engage but different gear speeds are obtained by merely tightening brake bands on gear drum. It consists of a ring gear annular wheel, sun gear and planet gears with a carrier. In order to obtain different speeds, any one of these units can be held from rotation by means of brake bond. The ring gear contains teeth on its inner circumference and is surrounded by a brake band. The brake band is operated by a gear stick or lever to grip the ring gear and hold its movement. The sun gear is attached to the clutch shaft thus moves along with the movement of the engine crankshaft. The planet gears are in constant mesh with both the sun gear and ring gear and are free to rotate on their axes carried by the carrier frame which in turn is connected to the driver shaft.When the ring gear is locked by the brake band, the rotating sun gear causes the planet gears to rotate. Since the ring gear cannot move. The planet gears are forced to climb over it. During this position, the ring gear acts as a track for the planet gears to move over. The driven shaft which is connected to the planet gear carrier is thus rotated. When the ring gear is released, it is free to move in consequence to the rotation of planet gears which rotate around their axis. During this position, there is no movement of planet carries and hence the driven shaft remains stationary. A planetary gearbox contains a number of such units to obtain various speed reductions.
- Hydraulic torque converter: Hydraulic torque converter is same as the electric transformer. The main purpose of the torque converter is to engage the driving member to driven member and increase the torque of driven member. In the torque converter, an impeller is bolted to the driving member, a turbine is bolted on the driven member and stationary guide vanes are placed between these two members. This all parts are enclosed in a single housing filled with hydraulic liquid. The impeller rotates with the driven member and it through the liquid outward by centrifugal action. This liquid flowing from the impeller to turbine runner exerts a torque on the stationary guide vanes which change the direction of liquid, thereby making possible the transformation of torque and speed. The difference of torque between impeller and turbine depends upon these stationary guide vanes. This serves as the function of both gearbox and clutch.
- Manual Transmission Gearbox:
In this type of transmission, different speed ratio or gear ratio is selected by the driver manually. According to their design, this is subdivided into three types-
- Sliding mesh gearbox: This is one of the oldest types. It this, gears on the main shaft are moved right or left for meshing them with appropriate gears on the countershaft for obtaining different speed. This type of gearbox derives its name from the fact that the gears are meshed by sliding. One disadvantage of it is that special skill is required to operate this gearbox.
- Constant mesh gear box: In this gearbox, all the gears are in constant mesh with each other all the time. The gears on the main shaft rotate freely without rotating the main shaft. Constant mesh gear box consists two dog clutches. These clutches are provided on the main shaft, one between the clutch gear and the second gear and the other between the first gear and reverse gear. When the left side dog clutch is made to slide left by means of the gearshift lever, it meshes with the clutch gear and the vehicle runs at top speed. If this clutch slides right and meshes with a second gear than the vehicle runs on second gear speed. So in constant mesh gearbox, we can change the gear ratio by shifting the dog clutch. This type of gearbox is more popular than sliding mesh because it creates low noise and less wear of gears.
- Synchromesh gearbox: This gearbox is same as the constant mesh gearbox except dog clutch is replaced by synchromesh devices. Synchromesh gear devices work on the principle that two gears to be engaged are first brought into frictional contact which equalizes their speed after which they are engaged readily and smoothly. The synchromesh looks like as the cone clutch where the outer surface of cone consists the frictional surface. This type of gearbox is widely used in an automobile.