Synchromesh gearbox transmission system is an extension of a constant mesh type transmission system. In 1928, Engineers from General Motors developed a Synchromesh transmission system in order to overcome the problems of the constant mesh transmission system.
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| Example of Synchromesh Gearbox |
In the Synchromesh gearbox system, the dog clutch from the constant mesh gearbox is replaced with the synchromesh device. This synchromesh device makes the gearbox more compact, smooth, and noise-free operation of gears.
Usually, it comes with 5 speed 1 reverse manual transmission configuration. The best example of it is Maruti Suzuki Swift model.
Why there is a need for Synchromesh Gearbox?
- Gear shifting response in constant mesh gearbox was not quick because the dog clutch used in constant mesh gearbox needed to mesh with pair of gears which is not a quick and fast responsive task.
- In the constant-mesh gearbox, there was a lack of a mechanism that can bring all the rotating shafts i.e. clutch shaft, layshaft, main shaft at the same rotating speed which was responsible for the harsh shifting of gears.
- This caused more wear and tear of the dog clutch resulting in more maintenance of the system.
- The constant-mesh gearbox was not that compact and it has to be less noisy.
These problems lead the engineers from General Motors to develop a special type of gearbox popularly known as Synchromesh gearbox which will overcome all the above problems.
Table of Contents
Synchromesh Gearbox Construction and Working
The synchromesh gearbox is an extension of the constant mesh type gearbox.
Synchromesh type of gearbox is used over the constant type of gearbox because constant mesh type suffers from the problem of clashing of dog clutch due to the large difference in speeds of engaging gears.
Synchromesh gears ensure initial frictional contact amongst mating parts of gears to equalize the speed of gears pair and then push for smooth engagement of dog clutch with gear on the main shaft.
Construction of Synchromesh Gearbox
- Clutch shaft
- Layshaft
- Main shaft
- Reverse idler shaft
- Bearing
- Transmission gears
- Synchromesh device/synchronizer
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| 3D view of Synchromesh Gearbox |
The Clutch shaft is the input shaft of the gearbox as it is connected to the output shaft of the engine.
Layshaft is the intermediated shaft on which gears are mounted which transmits power from the clutch shaft to the output shaft.
The main shaft is the splined output shaft. Synchronizers and gears are mounted on the main shaft.
Synchronizers are special shifting devices that have conical grooves cut over their surface which provides frictional contact to the gears that are meshed to equalize the speed of the clutch shaft, layshaft, and main shaft. This provides smooth shifting of gears.
Clutch Shaft
- It is the input shaft to the gearbox.
- Its outer end is connected to the clutch disc.
- It has a gear machined at its inner end that meshes with a respective gear on the layshaft.
Lay Shaft
- The layshaft is freely suspended in bearing mounted on the transmission case.
- It has gears rigidly mounted/machined on it.
Main Shaft
- It is the output shaft of the gearbox.
- It has splines cut across its length to accommodate axial movement of gears on it.
- its outer end is connected to the propeller of the shaft through a universal joint.
Bearings
- Generally, taper roller bearings are used.
- These bearings are required to take radial and thrust loads during gear engagement.
Reverse idler shaft
- It is a short shaft that supports the reverse idler gears.
Transmission gears
- In synchromesh gearboxes, generally helical gears are used.
- These gears can be grouped into
Gears on the clutch shaft – rigidly attached/machined
Gears on layshaft – rigidly attached/machined
Gears on main shaft – free to rotate on main shaft
Gears on reverse idler shaft – rigidly attached/machined
Synchromesh Devices
- It consists of sliding dog members
Selector mechanism
- The selector mechanism employed is similar to that used on the sliding mesh gearbox.
Transmission case
- It provides support for bearings and shafts.
- It also provides an enclosure for lubricating oil.
- Generally, it is made up of aluminum to reduce weight.
- It has a vent on its top surface to ensure atmospheric pressure inside the gearbox.
Working of Synchromesh Gearbox
Advantages of Synchromesh Gearbox
- Synchromesh gearbox creates negligible noise during engagement and disengagement of gear.
- Avoids double-declutching.
- Quick shifting of gears.
- Compact in size.
- Used in most modern cars.
- No wear and tear of gears.
- Low vibration.
Disadvantages of Synchromesh Gearbox
- Expensive due to more number of gears and high manufacturing costs.
- Not capable enough to handle high loads.
- Damage possibility due to improper handling is high.
