The transmission system of a motorcycle consists of primary deceleration, clutch, gearbox, and secondary deceleration.
1. Primary deceleration
The primary deceleration is mainly composed of the driving sprocket (drive gear) mounted on the crankshaft end, the sleeve roller chain and the driven sprocket (driven gear) on the clutch, which acts as a primary deceleration and transmits the engine power to the clutch.
2. Clutch
Motorcycle clutches have the following structural types:
(1) Wet multi-plate friction clutch The clutch assembly is immersed in oil and is divided into three parts: active, driven and separated. The power of the engine is driven by the sprocket-type gear to drive the active cover. There are grooves on the periphery of the cover. There are five friction plates (active plates) embedded with rubber cork friction materials. The bumps on the outer edge are placed in the grooves of the active cover. It then rotates together as the active part of the clutch. Four steel follower pieces are connected with the follower piece fixing basin through the inner teeth to form the driven part. The main and driven plates are installed staggeredly, the fixed basin is connected with the main shaft of the gearbox with internal splines, and the four clutch springs on the gland press tightly against the friction plates and the driven plates to transmit the power to the gearbox. The clutch is of the normally engaged type. When the clutch handle is tightly squeezed through the steel cable, the screw sleeve rotates in the left cover, and the adjusting screw in the screw sleeve moves to the right, pushing the separation push rod and the gland, the spring pressure disappears, and the friction sign and the follower plate separation.
(2) The structure of automatic centrifugal clutch is used in light motorcycles such as Yamaha CY80 and Suzuki FR50, which automatically controls the separation and engagement of the clutch according to the level of engine speed. The clutch consists of active, driven and disengagement mechanisms. The active part is composed of clutch cover, thrust plate, clutch plate and so on. The driven part is composed of friction plate, center sleeve, etc. When the engine is running, as the speed increases, the centrifugal force generated by the steel ball also increases, and its axial component force overcomes the tension of the separation spring and moves outward along the groove in the clutch cover, pressing the thrust plate to tighten The clutch plate is pressed and the friction sign makes the clutch in the engaged state, and the power is output. When the engine speed is reduced to idle or flameout, the centrifugal force of the steel ball is reduced or not, and the tension of the separation spring overcomes the centrifugal force of the steel ball to make the steel ball return to its original position along the groove, and the clutch is separated.
(3) The structure of shoe block type automatic clutch is used in some miniature motorcycles. The active part is a fixed seat driven by the crankshaft. There are three shoe block assemblies on the seat, which are connected to the fixed seat with pins. The block is pulled toward the center of the crankshaft to maintain a certain gap between the shoe of the shoe block assembly and the clutch disc of the driven part. When the rotational speed increases, the centrifugal force generated by the shoe block is greater than the pulling force of the spring, and it is thrown outward. When the centrifugal force reaches a certain value, it engages with the clutch disc, and generates friction to drive the driven part to rotate and transmit power.
3. Secondary reduction and transmission
With different motorcycle models, there are three transmission modes: belt drive, chain drive and universal joint shaft drive. In miniature motorcycles, the belt drive is often used as the rear transmission device, and the size of the main and driven pulleys determines the secondary reduction ratio. Generally, motorcycles use chain drive for rear drive. Chain drive, simple structure, few parts, easy to manufacture and repair. There is a rear drive driving sprocket on the output shaft of the gearbox, and a driven sprocket on the rear wheel, which transmits power with a corresponding sleeve roller chain. In motorcycles with larger power engines (such as Yangtze River 750 motorcycles), its rear transmission mode adopts universal joint shaft transmission, and the rear wheel is equipped with a pair of helical bevel gears for auxiliary-level deceleration