The functions of differentials and differential lockers are fundamentally different. In order to help everyone understand these two devices, let’s talk about the difference between them today.
Open Differential
This is a structure that all modern cars have. It is used to solve the problem of wheel speed difference between the left and right wheels when turning. It is too obscure to explain the principle directly. Let me give you an example to make it clear. When we were in primary and secondary schools, we all had a sports meeting and walked through the entrance ceremony. Each class needed to walk around the playground track in a square formation. When the track turned, the students on the outside of the queue needed to walk in big steps, while the students on the inside walked slowly or even marked the spot. If the students on the inside and outside still maintained the previous speed when turning, then the team would definitely be scattered and unable to maintain integrity. This is actually similar to the role of the open differential in a car.
The open differential is composed of a driving gear, a driven gear, two side gears (also called sun gears), and two spider gears. Its core function is to allow the left and right wheels of the vehicle to always allow a speed difference to occur, and to transfer power to the wheel on the side with less rolling resistance, so that the vehicle can travel more smoothly in curves. However, this also creates a problem, that is, when the vehicle is on a slippery road or driven fiercely, the inherent structure of the open differential will transfer power to the wheel with poor grip (because of the small rolling resistance), then the vehicle will not be able to drive normally, and the limited slip differential we will talk about below is needed.
LSD limited slip differential
Limited slip differential, also known as Limited Slip Differential, or LSD for short. As the name implies, it is an improved differential that limits wheel slippage, and refers to a type of differential that allows the speed difference of the driving wheels on both sides to be within a certain range to ensure normal cornering and other driving performance. In fact, LSD can be divided into several forms according to different structures, and each type of LSD also has its own special features, including torque sensing LSD, helical gear LSD, ball lock LSD, viscous coupling LSD, mechanical LSD and other LSDs of different structures. I will not explain them one by one here, but remember that no matter which type of LSD limited slip differential, it can distribute power to the non-slipping wheel when one side of the wheel slips.
The above describes two common differentials. Of course, there are many more in the large family of differentials, including Torsen type and multi-plate clutch type. The Torsen and multi-plate clutch types are not only placed on the front and rear axles as differentials to distribute power to the left and right wheels, but are also placed behind the gearbox as a central differential to distribute power to the front and rear axles. We have already introduced them in the previous four-wheel drive system article, so we will not go into details today. Let me introduce you to the differential locker.
Electric differential locker
Although the LSD limited slip differential is very powerful, it is still not enough for off-road vehicles. In extreme off-road conditions, it is very important to keep the power distribution between the left and right wheels at 1:1, and this is when the differential lock comes into play. The electric differential locker is the most primitive, simple and reliable type of differential lock. When the driver manually locks the electric differential locker, the differential lock is hard-connected inside, and the left and right wheels will no longer be allowed to have a speed difference. The wheels on both sides can always get 50% of the power distribution. This is very useful for off-road vehicles in road conditions such as shell pits and cross axles. If there is no differential lock, the vehicle cannot pass through such road conditions, and the power will always be transferred to the slipping wheels.
Automatic differential locker
The electric differential locker is simple and reliable. It is a commonly used differential lock mechanism in off-road vehicles. However, there is a fatal problem that it can only be opened and closed manually. If you forget to close the differential lock after passing the off-road road, it will cause damage to the half-axle and other transmission systems when driving on the paved road in a locked state. Therefore, the automatic differential locker came into being. Its working principle is similar to the LSD limited slip differential, but it will be more radical in the locking amplitude of the power and it is also a purely mechanical structure, so there will be no problems such as overheating and failure.
When the vehicle is driving normally, the automatic differential locker is no different from the ordinary open differential, allowing the wheels on both sides to have a speed difference. However, when one side of the wheel slips and the speed difference between the wheels on both sides reaches the preset value of the automatic differential locker, the mechanical structure inside the automatic differential locker will lock the differential, and the left and right wheels will obtain 1:1 power transmission. After the vehicle is driving normally, the mechanical mechanism will automatically unlock, and the vehicle can drive normally on the paved road again.
Conclusion
Compared with the electric differential locker, the automatic differential locker does not require manual control by the driver, which lowers the operating threshold and will not damage the half-axle transmission system due to forgetting to unlock. However, due to the inherent design of the mechanical structure, the automatic differential locker can only be locked when the vehicle slips.
