Sliding mesh gearbox: Definition, Diagram, Construction, Working with Pdf

What is sliding mesh gearbox?

The 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.

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

Sliding mesh gearbox diagram:

Sliding mesh gearbox construction:

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

1. Engine Shaft
2. Output Shaft
3. Lay shaft
4. Clutch Gear
5. Fixed Gears on the lay shaft
6. Gears on Output Shaft
7. Gear shifting mechanism
8. Gear Pedal
9. Idler gear

1) Engine Shaft:- Engine Shaft has clutch gear fixed on it one end. Another end of the engine Shaft gets power from the engine.
Clutch gear is engaged with gear 4 which is mounted on a lay shaft, Therefore power transmission starts from the engine shaft to the lay shaft.

2) Lay shaft:- Lay shaft has 4 fixed gears which are gear 1, gear 2, gear 3, and 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 a lay shaft.

• Read here: Synchromesh gearbox

3) Output Shaft:- It is a spline shaft. It has three gears ( gear A, gear B, and gear C). 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 the lay shaft.

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

5) Fixed Gears on the 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 the lay shaft.

6) 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 the 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 slide to mesh (engage) with gears on the lay shaft.

7) 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 shifts the gear pedal to achieve desired gear, through the gear shifting mechanism, gears on the output shaft slide to mesh (engage) with gears on the lay shaft.

8) Gear Pedal:- The Gear pedal is connected to gears on the output shaft through a gear shifting mechanism. When the driver shifts the gear pedal to achieve desired gear, through the gear shifting mechanism, gears on the output shaft slide to mesh (engage) with gears on the lay shaft.

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

Hence Idler gear is used 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.

• Read here: Constant Mesh Gearbox

Sliding mesh gearbox working:

In a sliding mesh Gearbox, when the driver presses the gear pedal, the Gear slides (moves) on the output shaft and meshes with gears on the 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 meshes with gears on the lay shaft hence power only transmits from the engine shaft to the lay shaft.

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

First Gear:-

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

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:-

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:-

It is achieved when gear A directly meshes with clutch gear. Hence power transmits from gear clutch gear to the 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) rotate at the same speed.

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

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:

A sliding mesh gearbox has the following advantages:

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

Sliding mesh gearbox disadvantages:

A 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.

Sliding mesh gearbox applications:

The 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.

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