Automobile

Understanding Limited Slip Differential

A limited-slip differential (LSD) allows the two output shafts to rotate at different speeds while limiting the maximum difference between them. it is also known as self-locking differential or differential lockout.

In this article, you’ll get to know the definition, applications, diagram, types, working, advantages, and disadvantages of Limited slip differential.

limited slip differential

What is limited-slip differential (LSD)?

By shifting torque between the driven wheels, a limited-slip differential (abbreviated as LSD) allows for faster cornering. This allows the car to make the most of its engine’s output by reducing wheelspin and maximizing traction. It is a type of differential that allows its two output shafts to rotate at different speeds but limits the maximum difference between the two shafts.

Read more: Understanding differential

Applications

The applications of the limited-slip differential gearbox are commonly used in off-road and high-performance all-wheel-drive vehicles. It is also used handy on icy or dirt roads. Finally, limited-slip differentials are commonly used on performance cars such as BMW, Audi, Lexus, Dodge, Cadillac, and many others.

 

Diagram of limited-slip differential:

 

Types of a limited-slip differential

The followings are the common types of a limited-slip differential.

Fixed Value LSD:

Regardless of the torque input to the differential or the speed difference between the two outputs, the maximum torque difference between the two outputs, Trq d, is a constant value in this differential. Typically, spring-loaded clutch assemblies were employed in this differential.

Torque Sensitivity LSD:

Helical gears, clutches, or cones (an alternate type of clutch) are used in these limited-slip differentials, and the engagement force of the gears or clutch is a function of the input torque delivered to the differential (as the engine applies more torque the gears or clutches grip harder and Trq d decreases).

Torque detecting LSDs react to driveshaft torque, therefore the higher the driveshaft input torque, the tighter the clutches, cones, or gears are squeezed together, and the closer the drive wheels are coupled. Some contain spring loading to produce some tiny torque such that the drive wheels are minimally connected with little or no input torque (trailing throttle/gearbox in neutral/main clutch depressed). The amount of preload (therefore static coupling) on the clutches or cones is determined by their overall condition (wear) and the tightness with which they are loaded.

Read more: Types of differential and their functions

Clutch, Cone-type, or Plate LSD:

The clutch is made up of a stack of thin clutch discs, half of which are connected to one of the driving shafts and the other half to the spider gear carrier. The clutch stacks may be present on both or only one of the drive shafts. If there is only one, the spider gears connect the surviving driveshaft to the clutched drive shaft. The clutches are replaced by a pair of cones that are squeezed together to provide the same effect in a cone type.

2-Way, 1-Way, 1.5-Way:

Load, no-load, and overrun are the three input torque states. The coupling is proportional to the input torque during load situations, as previously indicated. The connection is reduced to a static coupling when there is no load. The behavior of the LSD on overrun (especially rapid throttle release) indicates whether it is a one-way, 1.5-way, or two-way system.

In both the forward and reverse directions, a 2-way differential will have the same limiting torque Trq d. This means that under engine braking, the differential will provide some restricting action.

Geared LSD:

Worm gears and spur gears are used to transfer and differentiate input power between two driving wheels or front and back axles in geared, torque-sensitive mechanical limited-slip differentials. This is not to be confused with the most typical beveled spider gears found in most automobile applications. The gears are pressed against the walls of the differential housing as torque is applied, causing friction. The limiting torque Trq d is created by friction resisting the relative movement of the outputs.

Speed Sensitivity:

Based on the difference in speed between the two output shafts, speed-sensitive differentials limit the torque difference between the outputs, Trq d. As a result, the differential’s behavior for minor output speed variations may be quite similar to that of an open differential. The limiting torque increases as the speed gap grows. When compared to a torque-sensitive differential, this results in a distinct dynamic behavior.

Read more: Understanding the working of a flywheel

Viscous LSD:

Because it relies on hydrodynamic friction from fluids with high viscosity, the vicious kind is often simpler. Silicone-based oils are frequently employed. A cylindrical chamber of fluid-filled with a stack of perforated discs spins in tandem with the output shafts’ normal motion. The chamber’s interior surface is connected to one of the driveshafts, while the outside is connected to the differential carrier. In the stack, half of the discs are connected to the inner, while the other half are connected to the outer. Differential motion causes the interleaved discs to move against each other through the fluid. When the speed of some viscous couplings is maintained, the fluid will heat up owing to friction.

Electronic LSD:

A planetary or bevel gear set comparable to that of an open differential and a clutch pack similar to that of a torque-sensitive or gerotor pump-based differential are common features of an electronic limited-slip differential. The clamping force on the clutch in the electronic unit is controlled externally by a computer or other controller. This enables the differential’s limiting torque, Trq d, to be regulated as part of a comprehensive chassis management system.

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components of limited slip differential

Read more: Understanding automobile clutch

Working Principle of a limited-slip differential

In most cases, the standard differential is sufficient. On the extremely slick ground, such as icy or muddy roads, a lack of driving power, known as traction force, can cause the rear wheels to slip because the typical differential will drive the wheel with the least traction. The ring gear and differential case will drive the pinion gears if one drive wheel is on dry pavement and the other is on ice or mud. The pinion gears, on the other hand, will not drive both side gears.

On dry pavement, the pinion gears will stroll around the side gear corresponding to the wheel when driven by the differential case. The pinion gears drive the slipping wheel, and the car will not move as a result. Almost all of the engine’s power is sent to the sliding wheel through the conventional differential. Differential locks can be used to solve this problem. Differential locks solve traction issues by distributing the same amount of power to both wheels while still allowing the vehicle to turn normally.

The limited-slip differential (LSD) in the differential case limits the differential rpm between two wheels, two thrust washers, and a clutch plate. When the left-side differential gear’s resistance is greater than the wheel’s, the right-side differential gear rotates. It causes the right-side differential clutch member’s teeth to climb the left-side differential clutch member’s teeth. As a result, it causes two clutch members to move away from one another.

As a result, the thrust washers are forced against the side gears. As a result of the friction between side gears and thrust washers, the rpm of the rear axle shafts approaches the differential case. As a result, it’s known as the limited-slip effect.

Watch the video below to learn more about the working of limited-slip differential:

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Advantages and disadvantages of Limited slip differential LSD

Advantages:

Below are the benefits of limited-slip differential LSD in their various applications:

  • A limited-slip differential boosts the car’s performance and speed by increasing the amount of traction it creates.
  • A limited-slip differential improves a vehicle’s safety by giving the driver more control over the vehicle.
  • Consider how a typical (or “open”) differential performs in off-roading or snow scenarios where one wheel begins to slip. With a typical differential, the non-contacting or slipping wheel will get the majority of the power (in the form of low-torque, high-rpm spinning), while the contacting wheel will remain stationary concerning the ground.

Disadvantages:

Despite the good advantages of LSD, some limitations still occur. Below are the disadvantages of a limited-slip differential.

  • The design is complex
  • Maintenance cost is high

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  • Conclusion

Limited-slip differential LSD which is also known as self-locking differential or differential lockout is a better way of achieving faster cornering. It allows cars to make the most of their engine’s output by reducing wheelspin and maximizing traction. It is a type of differential that allows its two output shafts to rotate at different speeds but limits the maximum difference between the two shafts. That’s all for this article, where the definition, applications, diagram, types, working, advantages, and disadvantages of Limited slip-differential are been discussed.

I hope you learn a lot from the reading, if so, kindly share with other students. Thanks for reading, see you around!