【正文】 aft coupling the transmission to the rear drive axle. Drive in through the layout of the bridge, the bridge drive shaft arranged vertically in the same vertical plane, and not the drive axle shaft, respectively, in their own subactuator with a direct connection, but the actuator is located at the front or the back of the adjacent shaft of the two bridges is arranged in series. Vehicle before and after the two ends of the driving force of the drive axle, is the subactuator and the transmission through the middle of the bridge. The advantage is not only a reduction of the number of drive shaft, and raise the driving axle of the mon parts of each other, and to simplify the structure, reduces the volume and quality.Fig 2 Rearwheeldrive axleSome vehicles do not follow this typical example. Such as the older Porsche or Volkswagen vehicles which were rear engine, rear drive. These vehicles use a rear mounted transaxle with halfshafts connected to the drive wheels. Also, some vehicles were produced with a front engine, rear transaxle setup with a driveshaft connecting the engine to the transaxle, and halfshafts linking the transaxle to the drive wheels.Differential operationIn order to remove the wheel around in the kinematics due to the lack of coordination about the wheel diameter arising from a different or the same rolling radius of wheel travel required, interwheel motor vehicles are equipped with about differential, the latter to ensure that the car driver Bridge on both sides of the wheel when in range with a trip to the characteristics of rotating at different speeds to meet the requirements of the vehicle kinematics.Fig 3 Principle of differentialThe acpanying illustration has been provided to help understand how this occurs. drive pinion, which is turned by the driveshaft, turns the ring gear. ring gear, which is attached to the differential case, turns the case. pinion shaft, located in a bore in the differential case, is at right angles to the axle shafts and turns with the case. differential pinion (drive) gears are mounted on the pinion shaft and rotate with the shaft . side gears (driven gears) are meshed with the pinion gears and turn with the differential housing and ring gear as a unit. side gears are splined to the inner ends of the axle shafts and rotate the shafts as the housing turns. 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. it is necessary to turn a corner, the differential gearing bees effective and allows the axle shafts to rotate at different speeds .Openwheel differential on each general use the same amount of torque. To determine the size of the wheel torque to bear two factors: equipment and friction. In dry conditions, when a lot of friction, the wheel bearing torque by engine size and gear restrictions are hours in the friction (such as driving on ice), is restricted to a maximum torque, so that vehicles will not spin round. So even if the car can produce more torque, but also need to have sufficient traction to transfer torque to the ground. If you increase the throttle after the wheels slip, it will only make the wheels spin faster.Fig 4 Conventional differentialLimitedslip and locking differential operation Fig 5 Limitedslip differentialDifferential settlement of a car in the uneven road surface and steering wheeldriven speed at about the different requirements。 but is followed by the existence of differential in the side car wheel skid can not be effective when the power transmission, that is, the wheel slip can not produce the driving force, rather than spin the wheel and does not have enough torque. Good nonslip differential settlement of the car wheels skid on the side of the power transmission when the issue, that is, locking differential, so that no longer serve a useful differential right and left sides of the wheel can be the same torque.Limitedslip and locking differential operation can be divided into two major categories：(1) mandatory locking type in ordinary differential locking enforcement agencies to increase, when the side of the wheel skid occurs, the driver can be electric, pneumatic or mechanical means to manipulate the locking body meshing sets of DIP Shell will be with the axle differential lock into one, thus the temporary loss of differential role. Relatively simple structure in this way, but it must be operated by the driver, and good roads to stop locking and restore the role of differential. (2) selflocking differential installed in the oil viscosity or friction clutch coupling, when the side of the wheel skid occurs when both sides of the axle speed difference there, coupling or clutch friction resistance on the automatic, to make certain the other side of the wheel drive torque and the car continued to travel. When there is no speed difference on both sides of the wheel, the frictional resistance disappeared, the role of automatic restoration of differentials. More plicated structure in this way, but do not require drivers to operate. Has been increasingly applied in the car. About nonslip differential, not only used for the differential between the wheels, but also for allwheel drive vehicle interaxle differential/.Gear ratio The drive axle of a vehicle is said to have a certain axle ratio. This number (usually a whole number and a decimal fraction) is actually a parison of the number of gear teeth on the ring gear and the pinion gear. For example, a rear means that theoretically, there are teeth on the ring gear for each tooth on the pinion gear or, put another way, the driveshaft must turn times to turn the wheels once. The role of the final drive is to reduce the speed from the drive shaft, thereby increasing the torque. Lord of the reduction ratio reducer, a driving force for car performance and fuel econo