What exactly is the function of a multi-plate clutch limited-slip differential? Is it necessary for four-wheel drive vehicles?
If you are going to choose a fuel-powered four-wheel drive vehicle, you will probably notice a configuration called "multi-plate clutch limited-slip differential."
What exactly does it do? Is it the necessary and only configuration for a four-wheel drive?
Let's talk about this differential today, but you need to understand why differential is needed and what differential means. Refer to the picture below, which is just the turning radius of the car. Focus on the different turning radius of each wheel.
The wheel hubs and tire models of most cars are the same, which means that the front and rear wheels are of the same standard; only a few sports cars have rear wheels that are wider than the front wheels, and these cars will not be discussed. As long as the wheel hub and tire model are the same, the wheel circumference will be the same.
I think everyone knows the principle of a ballpoint pen. The reason why a ballpoint pen can write is that the ball on the pen tip can roll inside the pen tip; when rolling, it can dip in ink from the inside, and then roll it out and then apply it to the paper.
The wheels are like the balls of a ballpoint pen, except they don't leave marks on the ground.
If you tie a row of ballpoint pens together to draw a circle, the circumference and size of the drawn circle will be inconsistent. But have you ever thought that the rotation speed of the ballpoints is the same? As long as the ballpoints are the same size, this can still work. Did you draw a different circle?
Obviously not, because the balls are the same size and run at the same speed, the same amount of ink will be dipped in, and circles with the same circumference will be drawn under the same stroke - but the radius of each pen is different. In theory, it is forced To draw a circle, you have to draw circles with different circumferences; then the ball will compete with the paper and eventually the paper will be scratched.
On the contrary, if you want to draw a circle normally, you need to make the ball roll at different speeds.
This is easy to achieve, as long as you apply different forces to different pens when drawing a circle. The ball with a large force rotates fast, and the ball with a small force rotates slowly; for a car, the ball on each wheel The turning radius is different, but the circumference of the wheel is the same. If you want to turn normally (draw a circle), you have to make the wheel run at different speeds. This is the "differential speed", and the component that implements the differential speed function is called " Differential".
Both the front and rear axles of the car have differentials, but the rear axle of the front-wheel drive car does not have a differential, because the rear wheels are driven wheels and there is no contact between the two, so the natural drag force can be applied to the rear wheels on both sides. Different driving resistance; this resistance acts on the differential to perform differential transfer. Both the front and rear axles of rear-wheel drive and four-wheel drive vehicles have differentials. At the same time, the four-wheel drive part of rear-wheel drive vehicles also has differentials, of which the most commonly used is the "multi-plate clutch limited-slip differential"; four-wheel drive vehicles such as Haval H6, Envision S, Tiguan L, and Ruiji are based on front-wheel drive platforms. This limited-slip differential is used in all driving vehicles, and off-road vehicles based on rear-drive platforms such as Haval H9, Maxus D90Pro, Ford Everest, and Tank 500 also use this differential.
With this differential, it can ensure that the vehicle can use four-wheel drive on roads with high friction. The function of the limited-slip differential is to differentially transfer the front and rear wheels based on the running resistance of the front and rear drive shafts. This also ensures that the vehicle can Basic to normal cornering, these four-wheel drive vehicles have three sets of differentials.
The "multi-plate clutch limited-slip differential" has two functions. A part-time four-wheel drive only has front and rear axle differentials, and there is no differential in the transfer case; so this kind of four-wheel drive cannot be driven on the highway, but it can When off-road, it can ensure a 50:50 ratio of front to rear wheels to ensure that both the front and rear wheels have sufficient power to drive the vehicle out of trouble. On the contrary, if there is only an ordinary differential, if the front wheel friction is too low, too much or all of the power will be transmitted to the front wheels, and the rear wheels will lose power; because power and resistance are in opposition, small resistance will gain If there is more power, the vehicle will not be able to get out of trouble. If the rear wheel friction is small, the front wheels will lose power.
Therefore, when you want to go off-road, you still need to return to the state of part-time four-wheel drive. This is what the wet multi-plate clutch does; its function is to cancel the differential function of the differential and return to the state of part-time four-wheel drive. moving state.
However, the reliability of this wet multi-plate clutch is not high because it relies on compression to achieve a fixed ratio transfer; however, the wet multi-plate clutch itself has sliding friction, and long-term use of this mode can easily lead to high temperatures and Increased wear will reduce the life of the clutch assembly.
Therefore, real off-road vehicles do not use this structure. The ideal choice is a multi-plate clutch limited-slip differential with mechanical locking capability. When it is necessary to return to the part-time four-wheel drive state, it does not rely on the clutch friction plate, but mechanically The structure of the gear chain is combined with the transfer, so the reliability is much higher. The Tank 500, Patrol and Ford F150 Raptor all use this limited-slip differential, which is a true off-road vehicle.
In fact, the function of this part is the "differential lock", which uses a mechanical structure to lock the differential function of the differential.
Therefore, there are also some cars with open ordinary differentials and differential locks, such as the Land Rover Discovery 5. However, this combination does not have the intelligent transfer function of the multi-disc clutch limited-slip differential; and the Discovery 5 no longer uses high-speed differential. With its strong non-load-bearing body, this car is no longer strictly an off-road vehicle, but an SUV with certain off-road capabilities.