Limited Slip Differential or Self-Locking Differential or Differential Lockout
- The standard differential works well in most situations. However, on very slippery surfaces such as icy or muddy roads, a lack of driving force, called traction force, can cause rear wheels to slip because the standard differential will drive the wheel with the least traction.
- If one drive wheel is on dry pavement and the other is on ice or mud, the ring gear and differential case will drive the pinion gears. But, the pinion gears will not drive both side gears.
- When the pinion gears are driven by the differential case, they will walk around the side gear related to the wheel on dry pavement. It results in the pinion gears driving the slipping wheel and the vehicle will not move.
- The standard differential sends almost all engine power to the slipping wheel. This problem can be avoided by using differential locks. Differential locks overcome traction problems by sending the same power to both wheels while allowing the vehicle to make normal turns.
- The limited-slip differential (LSD) restricts the differential rpm between two wheels, two thrust washers and a clutch plate which are incorporated in the differential case shown in Figure
- When the resistance of left side differential gear is larger than the wheel, the right side differential gear will rotate. It makes the teeth of the right side differential clutch member climbing the teeth of the left side differential clutch member. So, it makes two clutch members move away from each other.
- Hence, the side gears are pushed against the thrust washers. Due to this, the rpm of the rear axle shafts comes closer to the differential case due to the friction between side gears and thrust washers. So, it is called the limited-slip effect.
Types of limited-slip differential:
The two most common types of limited-slip differential are as follows.
I. Clutch-plate differential
2. Cone clutch differential.
1. Clutch-plate differential:
The clutch-plate differential uses several friction discs which are similar to small manual clutch discs. The main difference between this limited-slip differential and a standard differential is the clutch packs placed between side gears and differential case. The clutch friction discs are made of steel covered with friction material. The clutch plates are made of steel. The discs and plates are alternately splined to the side gear and dogged (meaning tabs fit into grooves) to the differential case. Grooves in discs or plates are for better-grabbing power.
The pinion gears, side gears, and other parts are similar to a standard differential. The differential case of the limited-slip differential is made in two parts to allow for clutch pack removal. The discs and plates are applied by the preload springs and by the mechanical pressure of the pinion gears on the side gears. Since, the pinion and side gears are beveled gears, their teeth try to come out of engagement when the differential is transmitting engine torque.
It creates a pushing action on the side gears and forces them outward against the differential case. The outward pressure of the side gears presses the friction discs and steel plates together between side gears and case. Whenever the discs and plates are pressed together, the splined and dogged connections ensure the side gear: and differential cases are locked together.
When the vehicle is moving straight ahead, the clutch-plate differential operates similarly to a standard differential. The rear wheels and the differential case tum at the same speed. The clutch packs are applied but they are not needed.
When the vehicle is making a tum, a high torque caused by the outer wheel rotating faster than the case and it causes the clutch pack to slip. It allows the differential to operate similarly to a standard differential when making turns. The discs and plates slide against each other discs turn with side gears, plates turning with case allowing different rotating speeds between the case and side gears. Therefore, rear wheels rotate at different speeds.
2. Cone clutch differential:
It is the next version of the limited-slip differential. In place of clutch packs, the friction lined cones are used. The cone differential uses a cone-shaped clutch which engages a matching cone-shaped receptacle. The operation is similar to the clutch-plate differential.
Preload spring and side gear pressures force the cone into a dished depression in the differential case. Friction tries to lock the cone. Therefore, the side gear sends power to the wheel with the most traction. Both clutch-plate and cone differentials require a special limited-slip gear oil. Using ordinary gear oil in limited-slip differentials, it will cause the discs and plates or cones to slip and vibrate during turns.
Advantages of Limited Slip differential Gearbox :
- A limited-slip differential generates a higher level of traction, which increases the performance and speed of the car.
- A limited-slip differential increases the safety of a vehicle because it increases the control a driver has over the vehicle.
- The main advantage of a limited-slip differential is demonstrated by considering the case of a standard (or “open”) differential in off-roading or snow situations where one wheel begins to slip. In such a case with a standard differential, the slipping or non-contacting wheel will receive the majority of the power (in the form of low-torque, high rpm rotation), while the contacting wheel will remain stationary with respect to the ground.
Disadvantages of Limited Slip Differential Gearbox :
- Maintenance is more.
- Complex in design.
Applications of Limited Slip Differential Gearbox :
- Limited Slip Differentials are used in off-road and high-performance all-wheel-drive vehicles.
- Limited Slip Differentials are also used on handy on icy or dirt roads.
- Limited-slip differentials are commonly found on performance cars from BMW, Audi, Lexus, Dodge, and Cadillac, among many others.
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