附 录A一、英文原材料Drive AxleAll vehicles have some type of drive axle/differential assembly incorporated into the driveline. Whether it is front, rear or four wheel drive, differentials are necessary for the smooth application of engine power to the road.The drive axle must transmit power through a 90 angle. The flow of power in conventional front engine/rear wheel drive vehicles moves from the engine to the drive axle in approximately a straight line. However, at the drive axle, the power must be turned at right angles (from the line of the driveshaft) and directed to the drive wheels.This is accomplished by a pinion drive gear, which turns a circular ring gear. The ring gear is attached to a differential housing, containing a set of smaller gears that are splined to the inner end of each axle shaft. As the housing is rotated, the internal differential gears turn the axle shafts, which are also attached to the drive wheels.The differential is an arrangement of gears with two functions: to permit the rear wheels to turn at different speeds when cornering and to divide the power flow between both rear wheels.(1)The accompanying illustration has been provided to help understand how this occurs. The drive pinion, which is turned by the driveshaft, turns the ring gear.(2)The ring gear, which is attached to the differential case, turns the case.(3)The pinion shaft, located in a bore in the differential case, is at right angles to the axle shafts and turns with the case.(4)The differential pinion (drive) gears are mounted on the pinion shaft and rotate with the shaft.(5)Differential side gears (driven gears) are meshed with the pinion gears and turn with the differential housing and ring gear as a unit.(6)The side gears are splined to the inner ends of the axle shafts and rotate the shafts as the housing turns.(7)When both wheels have equal traction, the pinion gears do not rotate on the pinion shaft, since the input force of the pinion gears is divided equally between the two side gears.(8)When it is necessary to turn a corner, the differential gearing becomes effective and allows the axle shafts to rotate at different speeds.As the inner wheel slows down, the side gear splined to the inner wheel axle shaft also slows. The pinion gears act as balancing levers by maintaining equal tooth loads to both gears, while allowing unequal speeds of rotation at the axle shafts. If the vehicle speed remains constant, and the inner wheel slows down to 90 percent of vehicle speed, the outer wheel will speed up to 110 percent. However, because this system is known as an open differential, if one wheel should become stuck (as in mud or snow), all of the engine power can be transferred to only one wheel.Engineers searched diligently for ways to allow each driving wheel to operate at its own speed. Many ideas were tried with mixed results before the basic design for the present-day, standard differential was finally developed. The successful idea that is still used in principle today was to divide the engine power by dividing the axle in two-attaching each driving wheel separately to its own half-axle and placing in between, an ingenious, free-rotating pinion and gear arrangement. The arrangement was called the differential because it differentiates between the actual speed needs of each wheel and splits the power from the engine into equal driving force to each wheel.On/off road vehicles and other trucks required to haul heavy loads are sometimes equipped with double reduction axles. A double reduction axle uses two gear sets for greater overall gear reduction and peak torque development. This design is favored for severe-ser-vice applications, such as dump trucks, cement mixers, and other heavy haulers.The double reduction axle uses a heavy-duty spiral bevel or hypoid pinion and ring gear combination for the first reduction. The second reduction is accomplished with a wide-faced helical spur pin-ion and gear set. The drive pinion and ring gear function just as in a single reduction axle. However, the differential case is not bolted to the ring gear. Instead, the spur pinion is keyed to and driven by the ring gear. The spur pinion is in turn constantly meshed with the helical spur gear to which the differential case is bolted.Many heavy duty trucks are equipped with two rear drive axles. These tandem axle trucks require a special gear arrangement to deliver power to both the forward and rearward rear driving axles. This gearing must also be capable of allowing for speed differences between the axles. Two axle hub arrangements are available to provide support between the axle hub and the trucks wheels: the semi-floating type axle and the fully floating type axle. Of the two ,the semi-floating is the simplest, cheapest design to incorporate ,but the fully floating axle is more popular in heavy-duty trucks. In the semi-floating type axle, d