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Tham khảo tài liệu 'motorcycle mechanics 2009 part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Illlitlo Transmissions The motorcycle engine is a wonderful piece of engineering. It is light compact efficient and develops tremendous power for its size. Its one drawback like most internal combustion engines is that it is only really efficient over a relatively narrow range of rpm. At low rpm it doesn t develop much power while at high rpm it wears out quickly. These characteristics of the engine require that a multiple-speed transmission be used to allow the engine to operate in its efficiency range. The transmission allows the engine to run in this narrow rpm range while the rear wheel s rotating speed varies greatly. The typical motorcycle engine runs fast at 2000 rpm and up on most bikes. At 60 mph the rear tires are only turning about 800 rpm while the engine is revving about 4000 rpm. Since the engine must turn five times faster than the rear wheel an overall reduction of about 5 to 1 is required. Part of this reduction is provided by the primary drive which was covered in Unit 17. Other gear reductions are handled by the transmission which allows the rider to select from four to six different ratios on most machines. The lower ratio gears allow the engine to get the mass of the machine and rider underway without straining the clutch or engine itself. The high ratio gears allow the engine to operate in its efficiency range at faster cruising speeds. 196 Figure 18-1 shows a layout of the basic parts of the power train in a typical motorcycle. It shows the primary drive from the engine to clutch the clutch the transmission and the final drive from transmission to rear wheel . The transmission is located behind the engine and receives its power through the clutch. The clutch connects and disconnects the engine from the transmission to allow the rider to select various transmission ratios and to start and stop efficiently. GEAR RATIOS When a small gear drives a larger one there is an increase in torque or twisting force and simultaneously a decrease in rpm at
