One of the more impressive components in any automobile is the gearbox or “gearbox”. While most cars don’t benefit from the technology, the synchromesh is what the single-clutch manual gearbox is aiming for. At least for now.
A synchromesh is almost like a small clutch that sits on the output shaft between gears, slowing or increasing the required gear’s relative speed to perform a perfect meshing of teeth within the transmission.
What is Synchromesh Transmission?
Synchromesh transmissions are a further refined version of the constant mesh system, although less common. How it improves the system is by adding another stage to the process of connecting the gears to the drive shaft through the dog clutch.
It divides the dog clutch into two parts, a gear attached to the drive shaft called the synchromesh hub and a collar around the outside that can slide back and forth and is called the shift sleeve.
A new component was added to the gears themselves, the synchronizer cone, and another moving part called the synchronizer ring was introduced to surround the cone.
This is where things get a little complicated. The collars or shift sleeves are now the components controlled by the gear stick and they can slide halfway on the synchronizer rings in either direction.
This presses the rings against the synchronizer cones attached to the gears and, due to the increased friction caused by the widening cone, can either accelerate or decelerate the gear to match the speed of the shift sleeve and synchronizer hub.
As soon as the speeds are matched precisely enough, the sleeve can slide further over the locking ring and come into direct engagement with the cone and the gear wheel, whereby everything is connected and the power is transmitted to the drive shaft.
Incredibly, it all happens in the fraction of a second it takes to shift gears, giving you an even smoother gear change.
Why do We Need Synchromesh Transmission?
Since, the introduction of the transmission system from sliding mesh to constant mesh various modifications is made in both the systems to make them smooth, less noisy and to make the shifting response quick, though the constant mesh overcame the important limitations of sliding mesh gearbox like double-de-clutching, wear and tear but still has its own limitations, let’s discuss them:
- The response to the shifting of gears in the constant mesh gearbox is not quick as the dog clutches used in constant mesh gearbox has to mesh with the rotating pair of gears which is not a quick task.
- There is a lack of a mechanism in constant mesh gearbox that can bring all the rotating shafts that are clutch shaft, main shaft and lay shaft at the same rotating speed, which is responsible for the harsh shifting.
- The teethes of the dog clutches shows wear and tear which in turn increases the maintenance of the system.
- The shifting in constant mesh gearbox is a noisy process as the dog clutches has to make contact with rotating gear pair.
- The constant mesh gearbox is not compact as compared to a synchromesh gearbox.
These problems lead General Motors to develop a synchromesh gearbox which is still used in almost 52% of the automobile vehicles on the road today.
How Does a Synchromesh Work In a Gearbox?
A synchromesh system makes a gear shift smoother by refining the process of meshing two gears together.
First, a part called a gear hub is attached to the output shaft that leads to the wheels. A part called a shift sleeve can freely slide over the gear hub and mesh with the appropriate adjacent gear.
When this happens, the hub and the gear will spin together as a unit, and the wheels will spin based on the gear ratio of the selected gear.
However, since the gear hub and the appropriate gear are spinning at different speeds, they need help from the synchronizers. The shift sleeve needs to mesh with the appropriate gear in a fluid manner to avoid vibration, noise, and damage.
A shift sleeve is responsible for managing two numbered gears. So, for example, one shift sleeve is responsible for sliding back and forth between the first and second gear, while another shift sleeve is responsible for sliding back and forth between the third and fourth gear, and so on.
A part called the synchronizer ring is sandwiched between the shift sleeve and another component called a synchronizer cone. The synchronizer cone is located alongside the appropriate gear.
When the driver selects a gear by moving the gear lever, the shift sleeve will push the synchronizer ring into the synchronizer cone.
The synchronizer ring will then rub against the synchronizer cone like a clutch, increasing or decreasing the synchronizer cone’s speed depending on whether the driver is shifting up or shifting down.
The synchronizer ring and synchronizer cone have gears that align when they are synchronized. These gears will guide the shift sleeve into the appropriate gear.
What Is the Difference Between a Non-Synchromesh and Synchromesh Gearbox?
Non-synchromesh and synchromesh gearboxes are very similar. However, non-synchromesh gearboxes (sometimes called dog boxes in automotive applications) lack the refinement of a synchromesh gearbox.
Instead of using a synchronizer ring and synchronizer cone to combine the shift sleeve and the appropriate gear, non-synchromesh gearboxes have a dog clutch.
These dog clutches are essentially two opposing gears with large, squared teeth. However, one side has smaller teeth, so the two opposing gears don’t need to align perfectly to mesh together.
Unlike synchromesh gearboxes, dog clutches aren’t intended to rub and create friction. Dog clutches are meant to join the two gears by simply disrupting the momentum of the other gear.
Typically, non-synchromesh transmissions are found in race applications and motorcycles. On the other hand, synchromesh transmissions are what you’ll find in regular production cars.
Advantages of synchromesh gearbox
- Smooth and Noise free shifting of gears which is most suitable for cars.
- No loss of torque transmission from the engine to the driving wheels during gear shifts.
- Double clutching is not required.
- Less vibration
Disadvantages of synchromesh gearbox
- It is extortionate due to its high manufacturing cost and the number of moving parts.
- When teeth make contact with the gear, the teeth will fail to engage as they are spinning at different speeds which causes a loud grinding sound as they clatter together.
- Improper handling of gear may easily prone to damage.
- Cannot handle higher loads.