Kelly-Anne Kidston
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Onto the viscous coupling, and how it works. It’s easiest to understand this by looking at a scenario when one of the driven wheels has limited traction (let’s imagine it’s on ice) while the other driven wheel has plenty of traction (on pavement). With an open differential, torque is evenly split between the two wheels (50/50). Since a wheel on ice can’t supply much torque, the other wheel will have limited torque as well, and often the vehicle will not be able to accelerate (this is why locked differentials are so prevalent for off-road vehicles) 😊 With an LSD, you are able to transfer more of the torque to the wheel with more traction 🙌 [1]
Open differentials are the most basic form of a differential. The purpose is to allow for different speeds between the two wheels, while torque split had is held constant at 50/50. A common misconception with open differentials is that when one wheel is lifted, 100 per cent of the torque is sent to it. This is not true, however the amount of torque sent to the wheel with traction is very low because the amount of torque required to spin a wheel is also low. Remember, both wheels always receive equal torque, but if one has no resistance (eg. If it’s in the air), the amount of torque sent to the drive axle as a result is very low. [2]
The first and second images show the three pairs of worm gears meshed with each half of the axle – with the spur gears at the end of each worm connecting the pairs. It’s this connection that transfers torque from one wheel to the other, once one axle begins rotating faster than the other. While the first and second images are of the orginal torsen design, the third image is of the second version of the torsen differential. The newer design repositioned the worms gears to be inline with axles but still perform the same mechanical action. Each worm gear is still in contact with its pair, and only one side of the axle with spaces in the gear removing the mesh with the other side. [3]
Goodparts.com goes on to mention that the best way to transmit power to the rear wheels of a vehicle is with a solid axle between the wheels. Since the wheels are mechanically connected they will always turn at the same rpm. When traveling in a straight line 50% of the drive torque goes to each wheel. If one wheel loses traction it takes less torque to rotate and the torque is automatically applied to the wheel with the traction. If one wheel is lifted off the ground it will be taking 0% of the torque and the other wheel will get 100%. Of course a solid axle does not work very well if we want the vehicle to make a turn. In a turn the wheels on the outside of the turn have to rotate faster than the wheels on the inside of the turn. [4]
Article References
- https://www.carthrottle.com/post/engineering-explained-how-viscous-limitedslip-differentials-work/
- https://www.carthrottle.com/post/engineering-explained-the-best-kinds-of-differential-and-whats-most-suitable-for-you/
- https://www.matfoundrygroup.com/News and Blog/Types_of_Differential_and_How_They_Work
- https://www.goodparts.com/viscous-limited-slip/
