Here’s a clear explanation of a constant mesh transmission:
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Constant Mesh Transmission
A constant mesh transmission is a type of manual gearbox in which all gears on the main shaft and countershaft (layshaft) are always meshed together, but only one gear at a time is connected to the output shaft to transmit power to the wheels.
It is the most common type of manual transmission in modern cars because it provides smooth gear shifting and longer gear life.
1️⃣ Key Features
- All gears are always in mesh → reduces the risk of gear grinding.
- Power is transmitted only through the engaged gear → selected using a dog clutch (sliding collar).
- Dog clutches slide along the main shaft to lock a specific gear to the output shaft.
- Usually includes reverse gear using an idler gear.
2️⃣ Main Components
- Input Shaft (Primary Shaft): Connected to the engine via clutch.
- Layshaft (Countershaft): Always rotates; carries gears meshed with main shaft gears.
- Main Shaft (Output Shaft): Receives torque from engaged gear; drives the wheels.
- Dog Clutches (Sliding Collars): Engage selected gear to main shaft.
- Gears:
- Fixed gears: Permanently meshed on countershaft
- Free gears: Rotate freely on main shaft until engaged
- Reverse Idler Gear: Reverses rotation for backward movement.
3️⃣ Working Principle
- Driver moves gear lever → sliding collar moves → engages desired gear.
- Torque flows: Engine → Clutch → Input Shaft → Layshaft → Engaged Gear → Main Shaft → Wheels.
- Other gears remain unengaged and spin freely, reducing wear.
- Reverse gear uses idler gear to reverse rotation.
4️⃣ Advantages
- Prevents gear grinding → smoother operation.
- Durable gears
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