Pulleys are mechanical devices that are used to change the direction of force or change the speed of rotation. In motorcycles, pulleys are typically used in the drive train to transfer power from the engine to the rear wheel. There are two main types of pulleys used in motorcycles: drive pulleys and driven pulleys.
Drive pulleys, also known as crankshaft pulleys, are connected to the engine's crankshaft and are responsible for turning the drive belt, which in turn powers various motorcycle components such as the alternator, water pump and air compressor.
The driven pulleys, also known as transmission pulleys, are located at the rear wheel and are connected to the transmission. They are responsible for transferring power from the drive belt to the rear wheel, which drives the motorcycle forward. These pulleys are responsible for the final drive ratio, which determines how much torque is delivered to the rear wheel.
Both pulleys are usually made of aluminum or steel and have a series of grooves in which the drive belt sits, allowing the pulley to grip and transfer power. Pulley and belt wear can affect the performance of a motorcycle. It is important to check pulley and belt wear and replace them as needed.
In scooters, pulleys work in a similar way to motorcycles. The main difference is that scooters usually use a continuously variable transmission (CVT) system, which eliminates the need for gears and allows for smooth and effortless acceleration.
In a CVT system, power from the engine is transferred to a drive pulley, which is connected to the engine's crankshaft. The drive pulley is usually a thin, grooved wheel that is connected to a belt. The belt then wraps around the driven pulley, which is located at the rear wheel. The driven pulley is usually a larger, grooved pulley that is connected to the transmission.
When the engine revs up, the drive pulley spins faster, causing the belt to move up the grooves of the pulley. This causes the driven pulley to rotate faster as well, which in turn propels the scooter forward. The scooter's pulley system allows the engine to rotate at a constant RPM, while the rear wheel can rotate at different speeds. This is why scooters have a much smoother acceleration compared to motorcycles.
It is important to check the pulleys and belt wear and replace them as necessary, as worn pulleys or belts can affect the scooter's performance and can lead to failure. It is also advisable to read the owner's manual and follow the manufacturer's recommendations for replacement frequency.
A CVT transmission requires at least two pulleys to operate, transmitting torque through friction between the pulley surface and the drive belt. Therefore, the rim of the pulley must be a special groove with two symmetrical planes inclined at an angle to the axis of rotation. This inclination depends on the diameter of the wheel - the smaller it is, the sharper the angle. There are wheels with a narrow, normal and wide profile. Pulleys can have one or more grooves, in which case we are dealing with multi-groove belts. The runners of the passive pulley are compressed by a spring, this counteracts the reduction of the diameter of the surface on which the belt works.
The pulley transmits drive by friction across the surface of the pulley and the belt. With the correct combination of the two, the drive belt does not touch the bottom of the groove or protrude above the pulley rim. The belt must be sized to exclude the possibility of slippage. For proper interaction of the pulley and belt, it will also be important to keep the axis of rotation of both wheels parallel, which protects against premature wear of both components. Working pulleys do not cause noise, and the system has low inertia, which eliminates the possibility of significant overload.