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.
Earlier differential designs delivered the same amount of torque to each powered tire. The approach usually worked until one of the powered tires slipped. The other tire couldn’t compensate for the sudden imbalance.
In such a situation, a limited slip differential can direct more torque to a different tire that maintains its grip on the road surface. It can compensate for a powered tire losing traction, allowing you to retain control of your vehicle.
Last but certainly not least is the differential. It’s a gear assembly that splits the torque produced by the engine and delivers it to the wheels on the same drive axle. It also transfers the driveshaft’s motion to the axle that intersects with the shaft at a right angle.
Differentials come in several variants. The simplest one is the open differential, which uses interlocking gears to divide the torque between the wheels. In an open differential, each tire can rotate at a different speed when necessary.
Open differentials have several drawbacks. One of the most serious issues appears in vehicles that drive the wheels with the same axle. When you make a turn or drive in a curving path, tension accumulates in the outermost drive wheel. That wheel has to cover a greater distance, so it needs to spin much faster than the inner drive wheel. If the tension becomes too great, it causes the tire to slip. In the worst-case scenario, the driveshaft might break.
Thus, the open differential gave way to the limited slip differential. The newer differential variant restricts the difference in rotational speed between the two wheels, preventing slippage and relieving tension in the driveshaft.
When you put its component words together, eLSD refers to a limited slip differential with electronic controls.
The electronic limited slip differential comes into play when you make turns while driving your vehicle. When you drive in a straight line, the tires spin at the same speed. But when you make a turn, the tires on the side closer to the curb cover a shorter distance than the ones on the opposite, outermost side. The eLSD compensates for the difference in turning speeds, preventing slippage.
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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