The Differentials Thread
#1
04-15-2010, 06:49 PM
The Differentials Thread
Just thought I'd share my write-up on differentials I wrote for my site:
Some people will have to decide which rear differential will best fit their need. In this thread we will go over a multiple variety of differentials while also stating their pros and cons.
First question that some will ask is what is a differential, well a differential is a device that splits the engine torque two ways, allowing each output to spin at a different speed. Now your differential has three main jobs, no matter what type you have. These three jobs are:
Now we will talk about the different types of differentials.
Open Differentials:
This is the simplest type of differentials out there and this is the most common differential available on stock cars. An open differential allows for free slippage between the two sides of the axle. When a car is turning, the inner and outer wheels must rotate at different speeds.
Now the cons to an open differential is that it offers the least amount of traction. In a low-traction setting (dirt, sand, snow, ice, gravel), attempting to accelerate beyond the traction capabilities of the tires causes only a single tire to spin while the opposite tire generally does not spin at all or very little.
Limited Slip Differentials(LSDs):
A LSD is similar to an open differential in that it allows some slippage to occur, but it differs from an open differential by limiting the slippage, usually to a percentage difference. Under normal conditions, a LSD will allow minor slippage between the wheels. But when the slippage parsees beyond a pre-determined difference, after a slight delay, the axle sides lock together somewhat and send part of the rotational torque to the opposite wheel of the slipping wheel. These LSDs would normally be ideal for people who are into autocross and everyday driving, some also prefer them for occasional drag racing use as well.
Cons that come with the LSDs is they are clutch type differentials, which means the depend on friction that the clutch's provide to limit the speed differences between the drive wheels. Over time this clutches will wear and will require servicing. Also these types of differentials normally require a break-in period. If the break in period is not followed per the manufactures instructions, the LSD may be permanently harmed, in that it may engage and disengage erratically due to irregularities on and damage to the clutch surfaces.
Locking Differentials(Lockers):
A locking differential or locker is a variation on the standard differential. A locking differential may provide increased traction compared to a open differential by restricting each of the two wheels on an axle to the same rotational speed without regard to available traction or differences in resistance seen at each wheel.
The main lockers we would deal with for our cars are automatic lockers lock and unlock automatically with no direct input from the driver. Some automatic locking differential designs ensure that engine power is always transmitted to both wheels, regardless of traction conditions, and will "unlock" only when one wheel is required to spin faster than the other during cornering. They will never allow either wheel to spin slower than the differential carrier or axle as a whole. The most common example of this type would be the famous Eaton "Detroit Locker," also known as the "Detroit No-Spin," which replaces the entire differential carrier assembly.
Cons of these types of differentials are intensified tire wear, noticeable impact on driving behavior (most often tendency to under-steer also tendency of the rear swaying in wet conditions while in straight line driving.). Also these auto lockers are very noisy, emitting clicking sounds and loud popping sounds while engaging and disengaging.
Torsen Differentials:
The Torsen differential is a purely mechanical device; it has no electronics, clutches or viscous fluids. The Torsen (from Torque Sensing) 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.
These devices are often used in high-performance all-wheel-drive vehicles. Like the viscous coupling, they are often used to transfer power between the front and rear wheels. In this application, the Torsen is superior to the viscous coupling because it transfers torque to the stable wheels before the actual slipping occurs.
However, if one set of wheels loses traction completely, the Torsen differential will be unable to supply any torque to the other set of wheels. The bias ratio determines how much torque can be transferred, and five times zero is zero. One novel solution is to apply the brakes and the gas at the same time. This will create a level of "traction" on the spining wheel, and allow the Torsen differential to shift power to the other wheel.
Spools:
A spool is not technically a locker, but its ultimate purpose is to function as one. A spool is a unit that replaces the differential's side and spider gears essentially creating a solid axle. This forces both tires to always spin at the same rate. The advantage of this is guaranteed traction, but it comes at the expense of premature tire wear if the vehicle spends most of its time on pavement because one tire will always "skid" when turning sharp corners. It's also important to make sure each tire has equal air pressure or they will wear down unevenly and cause a loss in fuel economy. A spool is not typically recommended unless the vehicle will spend the majority of its life driving off-road where traction is essential (especially for rock crawling, mud, steep hills, and allout drag racing). A spool is the least expensive way to professionally lock the axle. Basically these would only be ideal for drag racing applications!
Hopefully this helps you understand what each one does.
Limited Slip | Autocross | Everyday Driving | Lite Drag Racing |
Open Diff. | Everyday Driving|
Locker | Drag Racing | Lite Everyday Driving |
Spool | Drag Racing Only|
Torsen | Everyday Driving | Autocross | Lite Drag Racing |
Feel free to add.
Some people will have to decide which rear differential will best fit their need. In this thread we will go over a multiple variety of differentials while also stating their pros and cons.
First question that some will ask is what is a differential, well a differential is a device that splits the engine torque two ways, allowing each output to spin at a different speed. Now your differential has three main jobs, no matter what type you have. These three jobs are:
- To aim the engine power at the wheels
- To act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before it hits the wheels
- To transmit the power to the wheels while allowing them to rotate at different speeds
Now we will talk about the different types of differentials.
Open Differentials:
This is the simplest type of differentials out there and this is the most common differential available on stock cars. An open differential allows for free slippage between the two sides of the axle. When a car is turning, the inner and outer wheels must rotate at different speeds.
Now the cons to an open differential is that it offers the least amount of traction. In a low-traction setting (dirt, sand, snow, ice, gravel), attempting to accelerate beyond the traction capabilities of the tires causes only a single tire to spin while the opposite tire generally does not spin at all or very little.
Limited Slip Differentials(LSDs):
A LSD is similar to an open differential in that it allows some slippage to occur, but it differs from an open differential by limiting the slippage, usually to a percentage difference. Under normal conditions, a LSD will allow minor slippage between the wheels. But when the slippage parsees beyond a pre-determined difference, after a slight delay, the axle sides lock together somewhat and send part of the rotational torque to the opposite wheel of the slipping wheel. These LSDs would normally be ideal for people who are into autocross and everyday driving, some also prefer them for occasional drag racing use as well.
Cons that come with the LSDs is they are clutch type differentials, which means the depend on friction that the clutch's provide to limit the speed differences between the drive wheels. Over time this clutches will wear and will require servicing. Also these types of differentials normally require a break-in period. If the break in period is not followed per the manufactures instructions, the LSD may be permanently harmed, in that it may engage and disengage erratically due to irregularities on and damage to the clutch surfaces.
Locking Differentials(Lockers):
A locking differential or locker is a variation on the standard differential. A locking differential may provide increased traction compared to a open differential by restricting each of the two wheels on an axle to the same rotational speed without regard to available traction or differences in resistance seen at each wheel.
The main lockers we would deal with for our cars are automatic lockers lock and unlock automatically with no direct input from the driver. Some automatic locking differential designs ensure that engine power is always transmitted to both wheels, regardless of traction conditions, and will "unlock" only when one wheel is required to spin faster than the other during cornering. They will never allow either wheel to spin slower than the differential carrier or axle as a whole. The most common example of this type would be the famous Eaton "Detroit Locker," also known as the "Detroit No-Spin," which replaces the entire differential carrier assembly.
Cons of these types of differentials are intensified tire wear, noticeable impact on driving behavior (most often tendency to under-steer also tendency of the rear swaying in wet conditions while in straight line driving.). Also these auto lockers are very noisy, emitting clicking sounds and loud popping sounds while engaging and disengaging.
Torsen Differentials:
The Torsen differential is a purely mechanical device; it has no electronics, clutches or viscous fluids. The Torsen (from Torque Sensing) 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.
These devices are often used in high-performance all-wheel-drive vehicles. Like the viscous coupling, they are often used to transfer power between the front and rear wheels. In this application, the Torsen is superior to the viscous coupling because it transfers torque to the stable wheels before the actual slipping occurs.
However, if one set of wheels loses traction completely, the Torsen differential will be unable to supply any torque to the other set of wheels. The bias ratio determines how much torque can be transferred, and five times zero is zero. One novel solution is to apply the brakes and the gas at the same time. This will create a level of "traction" on the spining wheel, and allow the Torsen differential to shift power to the other wheel.
Spools:
A spool is not technically a locker, but its ultimate purpose is to function as one. A spool is a unit that replaces the differential's side and spider gears essentially creating a solid axle. This forces both tires to always spin at the same rate. The advantage of this is guaranteed traction, but it comes at the expense of premature tire wear if the vehicle spends most of its time on pavement because one tire will always "skid" when turning sharp corners. It's also important to make sure each tire has equal air pressure or they will wear down unevenly and cause a loss in fuel economy. A spool is not typically recommended unless the vehicle will spend the majority of its life driving off-road where traction is essential (especially for rock crawling, mud, steep hills, and allout drag racing). A spool is the least expensive way to professionally lock the axle. Basically these would only be ideal for drag racing applications!
Hopefully this helps you understand what each one does.
Limited Slip | Autocross | Everyday Driving | Lite Drag Racing |
Open Diff. | Everyday Driving|
Locker | Drag Racing | Lite Everyday Driving |
Spool | Drag Racing Only|
Torsen | Everyday Driving | Autocross | Lite Drag Racing |
Feel free to add.
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