Synchromesh gearbox: Definition, Diagram, Working principle, Construction, Working, Advantages and disadvantages, Application [with Pdf]

What is synchromesh gearbox?

1) Synchromesh gearbox is the latest type of manual transmission gearbox.

2) In this gearbox, lay shaft gears are in constantly meshing with the gears on the output shaft as like a constant mesh gearbox.

3) But in Synchromesh gearbox, Instead of Dog clutch, Synchronizer Ring and Hub is used.

4) Synchronizer Ring helps in bring the all shaft speed to equal and Synchronizer Hub helps in smoothly engage the gears.

5) Synchromesh gearbox is invented by Earl Thompson in 1918.

Synchromesh gearbox diagram:-

synchromesh gearbox diagram

Construction:-

Synchromesh Gearbox Is consists of the following key components:-

  1. Engine Shaft
  2. Lay Shaft
  3. Output Shaft
  4. Gears on Lay shaft
  5. Gears on Output shaft
  6. Cone
  7. Synchronizer Hub
  8. Sliding Sleeve
  9. Synchronizer Ring

A) Engine Shaft:- Engine Shaft’s one end is connected to the clutch, hence when the clutch engages, the engine shaft rotates at the speed received from the engine.

On the other end of the engine shaft, the clutch gear is fixed.

Clutch gear constantly meshes with the lay shaft gear. Hence when the clutch is engaged, power transmission occurs from the engine shaft to the lay shaft.

B) Lay Shaft:- There are 5 fixed gears located on the lay shaft are gear1, gear2, gear3, gear4, gear5.

The Gear 5 is located on lay shaft meshes with clutch gear which rotates with power from the engine shaft.

C) Output Shaft:- There are 4 Gears on this shaft.

D) Gears on Lay shaft:- There are four gears fixed on the lay shaft. These gears are constantly meshing with the gears on the output shaft.

Hence power transmission occurs from the engine shaft to the gears on output shaft gears through the gears on lay shaft.

E) Gears on Output shaft:- These gears are located on the output shaft which are freely rotated on it.

Externally Cone shape cones are attached to the gears. Cones have Dog teeth for the Gear engagements..

When the driver shifts the gear, through the shift fork, Sliding sleeve press the Synchronizer Ring on the cone.

F) Cone:- It is an external cone shape part that is attached to the gears. Cones have Dog teeth for the Gear engagements.

As per movement of shift fork, sliding sleeve (having internal teeth) slides & internally meshes with the dog teeth of the cone.

G) Synchronizer Hub:- Synchronizer hub is fixed on the output shaft. It has external teeth for the sliding of the sleeve.

Sliding Sleeve is internally meshing with the Synchronizer hub. Hence sliding sleeve can slide in both directions.

H) Sliding Sleeve:- Sliding Sleeve is internally meshing with the Synchronizer Hub. Hence sliding sleeve can slide in both directions. It is used for the interlocking of Synchronizer Hub and Cone.

The gear lever is connected to the shift fork & the shift fork is connected to the sliding sleeve. Hence when the driver shifts the gear, the shift fork moves the sleeve on the hub.

I) Synchronizer Ring:- Synchronizer Ring has an internal cone shape to engage with the cone.

When Driver shifts the gear, the shift fork moves the sleeve, therefore the sleeve Presses the Synchronizer Ring inside the cone.

Synchromesh gearbox working principle:-

Synchromesh devices works

1) Externally Cone shape cones are attached to the gears. Cones have Dog teeth for the Gear engagements.

2) Synchronizer Ring has internal cone shape to engage with the cone.

3) Sliding Sleeve is internally meshing with the Synchronizer hub. Hence sliding sleeve can slide in both directions.

4) When the Driver shifts the gear, the shift fork moves the sleeve, therefore the sleeve presses the synchronizer ring inside the cone.

5) Hence due to friction between cone & synchronizer ring output shaft starts rotating with gears at the same speed.

6) Then sleeve engages on the dog teeth of cone hence in such way with the help of synchronizer devices smooth engagement dones & Power obtain at the output shaft.

Working of synchromesh gearbox:-

In the synchromesh gearbox, gear shifting is done with the help of a shift fork.

The gear lever is connected to the shift fork & the shift fork is connected to the sliding sleeve. Hence when the driver shifts the gear, the shift fork moves the sleeve on the hub.

When the sleeve moves on the hub, It presses the Synchronizer ring on the cone & then sleeve internally locks the cone & hub by internally meshing.

Due to the Synchronizer ring pressed on the cone, the Output shaft starts to rotate at the speed of gears. Hence Synchronizer ring helps in bring the speed of all shafts to the same.

A sliding sleeve helps in the engagement of gears by internally locks the cone & hub by internally meshing.

In a Neutral Position, the sliding sleeve is at the middle of the hub.

FIRST GEAR:-

synchromesh gearbox FIRST GEAR

When Sliding Sleeve 1 moves towards the left and press the Synchronizer ring 1 on the cone & then sleeve internally locks the cone & hub by internally meshing.

Hence Output shaft starts to rotate at a speed of gear A

Therefore In first gear, The power transmits from

Engine shaft to Clutch gear to gear 5 to lay shaft to gear 4 to gear A to output shaft

SECOND GEAR:-

synchromesh gearbox SECOND GEAR

When Sliding Sleeve 1 moves towards Right and press the Synchronizer ring 2 on the cone & then sleeve internally locks the cone & hub by internally meshing.

Hence Output shaft starts to rotate at a speed of gear B

Therefore In Second gear, The power transmits from 

Engine shaft to Clutch gear to gear 5 to lay shaft to gear 3 to gear B to output shaft

THIRD GEAR:-

synchromesh gearbox THIRD GEAR

When Sliding Sleeve 2 moves towards left and press the Synchronizer ring 2 on the cone & then the sleeve internally locks the cone & hub by internally meshing.

Hence Output shaft starts rotate at a speed of gear C.

Therefore In Third gear, The power transmits from

Engine shaft to Clutch gear to gear 5 to lay shaft to gear 2 to gear C to the output shaft

REVERSE GEAR:-

synchromesh gearbox REVERSE GEAR

When Sliding Sleeve 2 moves towards the Right and press the Synchronizer ring 2 on the cone & then sleeve internally locks the cone & hub by internally meshing.

Hence Output shaft starts to rotate at a speed of gear D

Therefore In Reverse gear, The power transmits from 

Engine shaft to Clutch gear to gear 5 to lay shaft to gear 1 to Idler gear to gear D to output shaft

5 speed 1 reverse synchromesh gearbox working video:-

Advantages and disadvantages of synchromesh gearbox:-

Advantages of synchromesh gearbox:-

The advantages of the synchromesh gearbox are as follows:-

  1. It provides smooth & quite shifting of gears due to use of Synchronizer Ring and Sliding sleeve.
  2. No need of skill to operate.
  3. It has more power transmission capacity as compared to constant mesh gearbox.
  4. No Double Declutching is required.

Disadvantages of synchromesh gearbox:-

The disadvantages of the synchromesh gearbox are as follows:-

  1. It is Bulky gearbox.
  2. It is Expensive.
  3. It requires more space.

Application of synchromesh gearbox:-

The application of synchromesh gearbox are as follows:-

  1. Sports Car
  2. Local Deliveries Trucks
  3. Wagon R Vxi

Thanks to:-

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