You may remember a previous post (TechTips 20), about 'Limited Slip Differential' implementations made with LEGO TECHNIC.
As a follow-up to that previous topic, lets take a look today into a more sophisticated and realistic solution, based on the Torsen Differential design.
The Torsen Differential or Torsen Traction, is another type of limited slip differential (LSD) used in automobiles. Torsen was invented by the American Vernon Gleasman and got its name from a contraction of Torque-Sensing.
It is a purely mechanical device which exploits the fact that worm gears cannot be back driven; it has no electronics, clutches or viscous fluids.
Works as an open differential when the amount of torque going to each wheel is equal. As soon as one wheel starts to lose traction, the difference in torque causes the gears in the Torsen differential to bind together.
The design of the gears in the differential determines the torque bias ratio. For instance, if a particular Torsen differential is designed with a 5:1 bias ratio, it is capable of applying up to five times more torque to the wheel that has good traction.
Compared to the example on the previous post above mentioned, this is a solution closer to that used in real mechanics, while it is not affected by the situation where the differential locks without slippage and due to small variations on wheel rotation speeds as the vehicle turns.
These devices are often used in high-performance all-wheel-drive vehicles.
The main advantage of a limited slip differential is shown by considering the case of a standard differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate or slip freely, and thus the vehicle will remain stationary.
In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use, such as driving in mud, off-road, or for high performance vehicles, the LSD can be employed to deal with it.
By limiting the angular velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some traction available on at least one of the wheels. This is achieved by locking the differential whenever a slip situation occurs.
Below some images that compare Conventional (left) and Torsen Differential (right) internal designs.
The first Torsen implementation made of LEGO, was done by Rob Stehlik back in 2002.
Below some pictures of his implementations. One first (left) closer to the real thing, and one further simplified LEGO version but still functional (right).
See Rob's webpage, for further details.
Or you may want to use the instructions and .Dat file under Mike Fusion's LEGO TECHNIC and MINDSTORMS page.
And below also some better photos taken from Mike Hatton's (Parax) reproduction.
Still confused about it
Ok, we may take a look at one video explanation by smellsofbikes...
Now as usual, some links with further info:
Learn more about, at HowStuffWorks:
- How Differentials Work
Learn more about, at Wikipedia:
And even an interesting related article, that I've found at a Meccano Club...
Main issues with the designs above, seems to be strength and the not so compact size. Thus some limited applicability into real models.
Meanwhile a Spanish reader (Carles Lacosta Morell), sent me images from a bit more compact design of is own. He is using two 36T Double Bevel gears for the structure, instead of the larger 40z ones above. Guess however the bias ratios, might be different as well.
And still some other Torsen images, found at BS, with a slightly different structure.
Since these same images appear replicated into several folders, don't know who's their original author.
Well... it seems I'm in risk of never finishing this post...
As Paul (Sariel) just commented, there is still a slightly smaller design from a LUGPol fellow.
Last Update: 2009.Mar.22 22:56 GMT