Rear axle limited slip differential/differential lock

[WapCar] The rear axle limited slip differential is located between the two rear wheels, which can compensate for the idling caused by the suspension of the wheels of the ordinary differential. At this time, the differential will continuously transmit the powerto the idling wheel without resistance, not only the vehicle can not be able to move forward, but also lots of the power will be lost. Generally the rear axle limited slip differential will be equipped on some high-performance vehicles. Vehicles equipped with the rear axle limited slip differential can also perform a large range of drift action during intense driving

Differential

Before that, let's first understand what a differential is and why is it necessary? As the name implies, differential is used to make the wheel speed difference, and in the case of turning, it can make the left and right wheels carry out a reasonable torque distribution to achieve reasonable turning effect. When driving in a curve, there is a certain difference in the  rotating speed of the wheels on the inside and outside, and the outer wheels have long driving distance and the rotating speed is higher than that of the inner wheels,  at this time, a differential is needed to adjust.

So how is this process achieved? First, let's take a look at the composition of an ordinary differential. The differential is mainly composed of planetary gear, gear rack and  left and right axle gear. At the junction of the drive shaft and the drive axle, we can see a driven gear with a relatively large radius. Because the radius of the driving gear of the input shaft is relatively small, a process of deceleration and torque increase can be realized in the process of the power transmission from this gear to the driven gear with a relatively large radius.

Next the driven gear of reducer drives the planetary gear to rotate together, since the left and right output shafts are connected with planetary gear carrier, the left and right output shafts will rotate together, and then the left and right axle gears will run together, and the key to acheive "different speed" is that the two planetary gears perpendicular to the left and right half shaft gears. The two planetary gears are meshed with the left and right wheels, and the gear meshing method allows the left and right gears to achieve a mutually resisting effect.

When the car is driving inline, the torque and rotating speed of the left and right axle gears are the same, so when combined with the planetary gears, the left and right sides can cancel each other out, and at this time, the planetary gears do not move. When encountering a turning situation, the inner wheel will recive more resistance than outer wheel, the torque of the left and right axle gears is different at this time, which will cause the rotation of the planetary gear. The planetary gear can give the inner gear a resistance torque to achieve deceleration, and at the same time can increase the speed of outer gear, so that the outer gear rotates faster than inner gear and a smooth turning is achieved.

Limited slip differential

The common differential has a disadvantage that because the wheels are suspended and cause idling, once this similar situation occurs, the differential will continuously transmit the power to the idling wheels without resistance, not only the car can not move forward, but also lots of power will be lost. At this time, a differential is needed to solve this problem, which is the limited slip differential introduced below.

Limited slip differential is abbreviated as LSD, the main function of LSD is to make the left and right wheels run together when working, and to control the rotating speed difference of the left and right wheels in a certain range, so that the vehicle can ensure normal driving. According to the difference of realization methods and machine structure, LSD can be subdivided into many types: torque sensing type, viscous coupling type, helical gear type, standard mechanical LSD and so on. Although the process of achieving the limited slip differential is different, and the final goal is the same.

When driving a car equipped with LSD and one of the driving wheels is idling, the LSD will control the power output of the two wheels and prevent the idling wheel stopping from continuing to idling, so that the other wheel has enough power to help the vehicle to move forward. When accelerating and cornering, the output torque and centrifugal force make the inner wheels of the vehicle lift off the ground or produce a slip phenomenon, and the LSD device will try to transfer the power to the outer wheels, so it can help the driver increase the speed of cornering, and thereby enhancing the handling performance.

Differential lock

The function of the differential lock is to lock the differential housing and half shaft lock together when one driving wheel slips, so that the differential loses the differential function and transfers all torque to the other side driving wheels. The differential lock is a good solution to the problem of power transmission that occurs when one side wheel is slipping, that is to the lock differential, so that the differential no longer works and the driving wheels on the left and right sides can obtain the same torque.

Rear axle differential lock

The rear axle differential lock is a locking mechanism installed on the central differential, which is placed between the rear wheels and is used to deal with the situation that the wheels lose adhesion and cannot get out of trouble. The differential lock and differential have completely opposite function, that is, the differential is not allowed to work and make the rotating speed of the vehicle on the both sides is the same. For example, when one side wheel is stuck and the other side wheel is slipping, the differential will work, because the function of the differential is to allow the speed difference between the wheels on the both sides, so that the stuck wheel remains stand still. And the wheel on other side will spin wildly due to the function of the differential, one side is stuck and one side spins wildly, so the vehicle will not be able to move forward and be trapped.

In order for the power to be transmitted to the "still" wheel normally, there must have the differential lock, which can rigidly connect the two half shafts to make it to whole, so that the wheels on the bothe sides can get the same power and make the vehicle get out of trouble, and this is the function of the differential lock. Typical cars with a front axle limited slip differential lock include Mercedes-Benz G-Class, Mercedes-Benz G-Class AMG, Wrangler Rubicon and other models.

Electronic differential lock

There are also so-called electronic differential locks on the market. In fact, the electronic differential lock does not have an objective entity, it is an extended function of the ABS/ESP system.   

Electronic differential lock is abbreviated as EDS, also known as EDL. It is an extended function of the ABS, which is used to identify whether the wheels of the car have lost the landing friction, so as to control the acceleration and skidding of the vehicle. It is relatively easy to understand the work principle of EDS. During the acceleration process of the car, when the electronic control unit judges that one side of driving wheel is slipping according to the wheel speed signal, the EDS will automatically start to work. The hydraulic control unit is used to brake the wheel with proper strength, thereby increasing the adhesion utilization rate of the driving wheel on the other side and improving the passing capability of the vehicle. When the driving condition of the vehicle returns to normal, the electronic differential lock stops working. Compared with ordinary vehicles, vehicles with EDS can make better use of ground adhesion to improve the vehicle's operability.