Sliding mesh gearbox: Definition, Diagram, Construction, Working, Advantages and disadvantages, Application [with Pdf]

What is sliding mesh gearbox?

1] Sliding mesh gearbox is the oldest type of gearbox in which gear shifting is carried out by sliding of certain output shaft gears and meshing with certain lay shaft gears.

2] It is one of the types of manual transmission gearboxes which was used in the oldest vehicles.

Sliding mesh gearbox diagram:

Sliding mesh gearbox diagram

Sliding mesh gearbox construction:

The sliding mesh gearbox is consists of the following key components:-

  • A) Engine Shaft
  • B) Output Shaft
  • C) Lay shaft
  • D) Clutch Gear
  • E) Fixed Gears on lay shaft
  • F) Gears on Output Shaft
  • G) Gear shifting mechanism
  • H) Gear Pedal
  • I) Idler gear

A) Engine Shaft:- Engine Shaft has clutch gear fixed on it one end. Another end of the engine Shaft get power from the engine.

Clutch gear is engaged with gear 4 which is mounted on lay shaft, Therefore power transmission starts from the engine shaft to the lay shaft.

B) Lay shaft:- Lay shaft has the 4 fixed gears which are gear 1, gear 2, gear 3, gear 4. Gear 4 meshes with clutch gear & receives power from the engine shaft.

When the lay shaft gears mesh with output shaft gears, power transmits from the engine shaft to the output shaft through lay shaft.

C) Output Shaft:- It is a spline shaft. It has three gears ( gear A, gear B, gear C, gear D ). These gears have internal splines hence these gears can easily slide on the output shaft and rotate with it.

The gear shifting mechanism is used in the gearbox to push output shaft gears.

When the output shaft gears mesh with lay shaft gears, power transmits from the engine shaft to the output shaft through lay shaft.

D) Clutch Gear :- Clutch gear is fixed at one end of the engine shaft. Clutch gear meshes (engages) with gear 4 on lay shaft, hence power transmits from the engine shaft to lay shaft.

E) Fixed Gears on lay shaft:- These four gears (gear1, gear2, gear3, gear4) are rigidly fixed on the lay shaft.

When these gears mesh with output shaft gears, power transmits from the engine shaft to the output shaft through lay shaft.

F) Gears on Output Shaft:- These gears has internal splines hence these gears can easily slide on the output shaft and rotate with it.

When the output shaft gears mesh with lay shaft gears, power transmits from the engine shaft to the output shaft through lay shaft.

The Gear pedal is connected to gears on the output shaft through a gear shifting mechanism.

The gear shifting mechanism is used to push output shaft gears (either on the left side or right side) on the output shaft.

This means when the driver shifts the gear pedal to achieve the desired gear, through the gear shifting mechanism, gears on the output shaft slides to mesh (engage) with gears on lay shaft.

G) Gear shifting mechanism:- Gear shifting mechanism is used to push output shaft gears (either on the left side or right side) on the output shaft.

One end of this mechanism is connected to the gear pedal and another end is connected to output shaft gears.

Therefore, when the driver shift the gear pedal to achieve desire gear, through the gear shifting mechanism, gears on the output shaft slides to mesh (engage) with gears on lay shaft.

H) Gear Pedal:- The Gear pedal is connected to gears on the output shaft through a gear shifting mechanism.   when driver shift gear pedal to achieve desire gear, through gear shifting mechanism, gears on output shaft slides to mesh (engage) with gears on lay shaft.

I) Idler Gear:- It is Separate Gear use in this gearbox. The idler gear is used in the gearbox, to achieve reverse gear.   When gear on lay shaft meshes (engage) with gears on output shaft, both rotate in opposite directions, which means vehicle runs to frontward.

Hence Idler gear is use between lay shaft gear and output shaft gear, therefore, both gears (lay shaft gear & output shaft gear) rotate in the same direction, which means the vehicle runs backwards.

Sliding mesh gearbox working:

In sliding mesh Gearbox, when driver press gear pedal, Gear slides (move) on the output shaft and meshes with gears on lay shaft. Therefore in such a way when gear meshes, speed/torque obtains at the output shaft.

In a Neutral position, output shaft gears are not meshed with gears on lay shaft hence power only transmits from the engine shaft to lay shaft
as shown in the above figure.

Therefore four gears positions we can obtain are as follows:-

First Gear:-

It is achieved when gear C moves towards left side and Meshes with a small Gear 2.   Hence small gear 2, transmits power to gear C.

Sliding mesh gearbox diagram First Gear

In the first gear, high torque and low speed are obtained at the output shaft.

Power Transmission= Engine Shaft->Clutch Gear->Gear 4->lay shaft->Gear 2->Gear C->Output Shaft

Second Gear:-

Sliding mesh gearbox diagram Second Gear

It is achieved when gear B moves towards the left side and meshes with gear 3. Hence gear 3 transmits power to gear B. In the second gear, medium torque and speed are obtained at the output shaft.

Power Transmission=Engine Shaft->Clutch Gear->Gear 4->lay shaft->Gear 3->Gear B->Output Shaft

Third gear:-

Sliding mesh gearbox diagram Third gear

It is achieved when gear A directly meshes with clutch gear. Hence power transmits from gear clutch gear to output shaft.

In the third gear, high speed and low torque are obtained at the output shaft. In the third gear, both shafts ( Engine shaft and Output Shaft) rotates at the same speed.

Power Transmission= Engine Shaft->Clutch Gear->Gear A->Output Shaft

Reverse Gear:-

Sliding mesh gearbox diagram Reverse Gear

It is achieved when gear C moves towards the right side & meshes with gear idler gear. Hence power transmits from gear 1 to gear C through Idler gear.

During reverse gear, gear 1 and gear C rotates in the same direction.

Power Transmission = Engine Shaft->Clutch Gear->Gear 4->lay shaft->Gear 1->Idler Gear->Gear C->Output Shaft

Sliding mesh gearbox advantages:

Sliding mesh gearbox has the following advantages:

  1. It is easy to manufacture.
  2. It has more efficiency as compared to constant mesh gearbox since only one gear is in meshing.

Sliding mesh gearbox disadvantages:

Sliding mesh gearbox has the following disadvantages:

  1. It has high tear and wear since more friction occurs.
  2. It requires more effort for the engagement of gears.
  3. It is large in size as compared to constant mesh gearbox.

Sliding mesh gearbox applications:

Sliding mesh gearbox is the old type gearbox that has applications in the oldest types of vehicles as follows:

  1. In Mercedes 35 HP
  2. In Fiat 6 HP
  3. In Alpha 12 HP.

FAQ’s:-

  1. What gear is used in sliding mesh gearbox?

    The spur type gears are used in the sliding mesh gearbox.

  2. What are the advantages of sliding mesh gearbox?

    Sliding mesh gearbox has the following disadvantages
    1] It has a high tear and wear since more friction occurs.
    2] It requires more effort for the engagement of gears.
    3] It is large in size as compared to a constant mesh gearbox.

  3. What is the difference between sliding mesh and constant mesh gearbox?

    In the sliding mesh gearbox only one gear is meshing but in the constant mesh gearbox, all gears are in constantly meshing.

  4. In what way a constant mesh gearbox is better than sliding mesh gearbox?

    In the sliding mesh gearbox, the chances of gear teeth failures are more because of continuous engagement of gears while in the case of a constant mesh gearbox, the dog clutch gets damaged not gears since gears are engaged by the dog clutch.

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