英语翻译
In passenger cars,the final drive usually consists merely of a hypoid bevel-gear drive.The geometry of the bevel-drive pinion and of the crown wheel determines the final-drive ratio (i0=2.24~4.93 for standard-production vehicles) (Fig.3-18).The hypoid gear is in common use today due mainly to the fact that the offset pinion allows the propeller shaft to be set below (for cars),or above (for commercial vehicles) the crown wheel center.This gives either a reduction in the propeller shaft tunnel,which causes a bump in the vehicle floor,or in the case of a commercial vehicle a reduction in the angle though which the universal joint has to operate.
In commercial vehicles,the necessary final-drive ratio can only rarely be accommodated in one stage (bevel-gear drive).For this reason,use is usually made of more elaborate final-drive systems:
1) single-reduction axle (up to i0=7) ,
2) transmission-type axle with front-or top-mounted bevel-gear drive,
3) double-reduction axle (total transmission ratio up to i0=9),
4) pinion axle (spur-gear drives in the wheel hubs),
5) planetary-hub reduction axle (also shiftable in special cases).
Large crown wheels reduce the ground clearance under the differential.In the case of pinion axles and planetary-hub reduction axles,the differential and the half-shafts can be made smaller by splitting the reduction.This makes it possible,even in the case of high power outputs,to achieve sufficient ground clearance of the vehicle.