Automakers sure love their acronyms, don’t they? Some abbreviations are straightforward–AWD stands for all-wheel drive, and 4WD is four-wheel drive. There is stuff like ABS, the anti-lock brake system, which makes you wonder where the L (for lock) went. Today, we’re looking at a specific term that appears more frequently in modern vehicles: eLSD, short for electronic limited slip differential.
“Electronic limited slip differential” is a mouthful because it includes three concepts in a single phrase: Electronic control, differential, and limited slip.
Let’s break down the major parts of eLSD:
The term electronic indicates the use of electronic devices to monitor, regulate, and run the system. If the control module detects that one of the wheels is slipping because the wheel is spinning too fast, the computer will engage the limited slip differential’s mechanisms automatically.
Speaking of tire slippage–limited slip refers to a type of differential that imposes a limit on the difference between the speeds of its output shafts. The shafts can still have different rotational speeds, but neither can rotate too fast compared to the other.
Non-limited slip differentials without electronic traction control will, when on ice, mud, or wet grass, allow the right hand wheel (forward gear) to receive all the torque while the left hand wheel sits there and does almost nothing. This causes you to get stuck.
Limited slip differentials will have a series of friction clutches between the axle gears and the differential carrier, with a big S shaped spring holding the axle gears against the clutches, which are able to slip under normal circumstances when the vehicle is turning but will prevent one wheel from spinning in wet grass or mud. Both wheels will receive torque all the time but with limited slip.
This type of differential requires a friction modifier fluid added to the gear oil to prevent the clutches in the final drive from chattering during turns.
The pinion gear transfers the driveshaft’s motion to the ring gear, which drives the carrier in which the small differential (spider) gears are housed.
Each axle has its own gear, and there are smaller pinion gears rolling on a shaft that passes through the center of the ring gear carrier. These smaller gears provide the connection between the ring gear carrier and the axle gears. During turns, these gears allow the axles to spin at different speeds.
The problem is that these gears will naturally deliver torque to the wheel with the least turning resistance, thus the spinning that happens on slippery surfaces.
The electronic limited slip differential engages when selected to provide even traction to both wheels using an electromagnetic coil. It can only be engaged at a stop or at less than 20 miles per hour and is used in extreme circumstances when maximum traction is necessary.
Some eLSDs feature a dedicated computer as their electronic brain. Others leverage the existing powertrain control module (PCM). Both types use wheel sensors to measure how fast the wheels are spinning and determine if they should apply extra torque to the appropriate tire.
In many models, the electronic limited slip differential is a part of the vehicle’s automotive chassis control or electronic stability control (ECS) system. Car manufacturers that produce vehicles with an eLSD include General Motors, Jeep, Mitsubishi, and Saab.
If the electronic limited slip differential is just a computerized LSD, is it worth the extra expense? What can it do that a manually operated limited slip differential cannot achieve?
Here are the benefits of using an eLSD over a standard LSD or other differential variants:
Computers react faster and work with higher precision than human beings. Thus, a computer-controlled electronic limited slip differential outperforms older differential designs. In particular, the eLSD improves your vehicle’s handling when changing lanes and turning around corners at high speeds.
The more capable eLSDs have pre-programmed settings for different road surfaces. Not all roads are equal–for example, gravel roads provide less road traction than pavement, and paved roads become more slippery when it rains or snows.
The electronic limited slip differential needs to take road surface friction into account if it wants to prevent tire slippage effectively. After all, the torque required to compensate for slippage on gravel roads isn’t the same as the torque for, say, mud. Switching to a torque distribution setting designed for use in the specific situation makes the job easier.
Vehicle yaw refers to how the vehicle rotates around its central point during a turning maneuver. Severe yaw can lead to the car or truck spinning out of control when making turns or changing lanes. Vehicles operating in AWD mode are highly vulnerable to vehicle yaw because they drive all four wheels, making it much easier for a wheel to slip.
Fortunately, the electronic limited slip differential can dampen vehicle yaw. Many AWD vehicles feature a rear eLSD system that aligns their rear end in the same direction as their front wheels. Thus, some drivers and mechanics refer to the eLSD as active yaw controls.
So, there you have it. The eLSD is short for electronic limited slip differential. It’s a useful technology that plays a major role in your vehicle’s handling and safety on the road.
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