Advanced Automotive Fault Diagnosis
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LÔØI NOÙI ÑAÀU, ledklok
| 10.3.3 Epicyclic gearbox
operation Epicyclic gears are a special set of gears that are part of most automatic gearboxes. They consist of three elements: ● a sun gear, located in the centre; ● the carrier that holds two, three, or four planet gears, which mesh with the sun gear and revolve around it; ● an internal gear or annulus is a ring with internal teeth, which surrounds the planet gears and meshes with them. Any part of a set of planetary gears can be held stationary or locked to one of the others. This will produce different gear ratios. Most of the auto- matic gearboxes of the type shown earlier have two sets of planetary gears that are arranged in line as shown in Figure 10.8. This provides the necessary number of gear ratios. The appropriate elements in the gear train are held stationary by a system of hydraulically operated brake bands and clutches. These are worked by a series of hydraulically operated valves in the lower part of the gearbox. Oil pressure to operate the clutches and brake bands is supplied by a pump. The sup- ply for this is the oil in the sump of the gearbox. Unless the driver moves the gear selector to operate the valves, automatic gear changes are made depending on just two factors: ● throttle opening a cable is connected from the throttle to the gearbox; ● road speed when the vehicle reaches a set speed a governor allows pump pressure to take over from the throttle. The cable from the throttle also allows a facility known as ‘kick down’. This allows the driver to change down a gear, such as for overtaking, by pressing the throttle all the way down. Many modern automatic gearboxes now use gears the same as in manual boxes. The changing of ratios is similar to the manual operation except that hydraulic clutches and valves are used. tải về 7.07 Mb. Chia sẻ với bạn bè của bạn:
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