Post by Reeper on Aug 6, 2007 19:31:20 GMT -5
Standard Carriers, Positraction & Limited Slips, Locking Differentials, Spools and Mini-Spools
Standard/Open Carrier:
Whenever a vehicle negotiates a turn, the outside wheel must travel farther (turn faster) than the inside wheel. This is accomplished by spider gears that allow the outside wheel to turn faster (this can be either the left or the right, but must be the outside wheel) than the ring gear, while the inside wheel turns slower than the ring gear. The net sum of the speed of the two wheels is twice as fast as the ring gear. That means if the outside wheel is turning 2 rpm faster than the ring gear, the inside wheel is turning 2 rpm slower than the ring gear. This differential action is very straightforward in a standard open differential and works great for more than 95% of vehicles on the road today.
When a vehicle with an open or a standard differential encounters a loose traction surface, it directs power to the wheel with the least resistance. The resulting action is the wheel on the loose surface spins, while the opposite wheel on the better traction surface stands still or barely transfers power. The reason a standard open differential works this way is because it is designed to provide equal force to both sides. If the wheel on either side looses traction, the other side suffers as well.
If, for example, the left wheel looses traction and cannot provide a resistance force back to the differential side gear, then the right side gear cannot transfer a force to the right wheel to counteract the slipping left wheel. The main point to remember is that an open differential provides equal POWER to both sides, not equal speed.
An open differential works just fine for 95% of vehicles on the road, since most people do not spin their tires often, if at all. For those of us who like to burn rubber or go off the dry pavement, there are now too many limited slip and locking differentials to choose from.
Positractions & Limited Slips:
Posis and limited slips transmit equal torque to both wheels when driving straight. However, when one wheel spins due to loss of traction, a patch of ice, mud, too much throttle, etc., the unit automatically provides more torque to the wheel that has traction. Recommended for daily driving, works well in ice, rain, mud and snow. However, in situations where absolute lockup is needed, a limited slip is not the best choice due to the fact that limited slips do slip in some situations.
Positraction is a type of limited slip. The name "positraction" was used by General Motors for their limited slip differential and the name has been associated with limited slips for many years.
Automatic Lockers:
Lockers (mechanical locking differentials) provide 100% transfer of power to both drive wheels. This power can be lost if both wheels spin, but a locking differential will never let one wheel spin free by itself while the other one sits still (unless the unit is broken). Automatic locking differentials are engineered to keep both wheels in a constant drive mode, yet have the ability to unlock to permit a difference in wheel speed while negotiating turns.
Recommended for serious off-roaders or serious hot-rodders, they can be annoying for everyday driving. The main shortcoming of automatic lockers is the noise inherent in their design. When getting on or off the throttle, they tend to bang or clunk, or sometimes make noise while disengaging when negotiating a turn. These characteristics are due to the design and a few locker manufacturers have come up with designs that make less noise, but no one has developed a perfectly quiet automatic locker yet. One more effect of lockers that hampers every day use is that they only drive the inside wheel on a turn, which can affect vehicle handling.
When driving the inside wheel, the vehicle tends to yaw from side to side slightly when negotiating a turn under power. When turning sharply while taking off from a stop, the inside wheel will tend to spin easily. This is especially prominent when taking off on a right turn, for two reasons: the torque on the rearend housing due to the driveline torque un-weights the right wheel, and right hand turns are tighter (because we drive on the right side of the road).
On-Command Lockers:
Many people want the benefits of a locking differential, but do not want the handling characteristics or noise of an automatic locker. There are a few on-command lockers available as an OEM option. These include the 1998 and newer Toyota Tacoma and Land Cruiser. These EOM designs use an electric motor or vacuum diaphragm to engage the locker. When it is not engaged, the unit acts like a standard open differential with no ill side effects aside from poor traction. When engaged, these units' lockup 100% and act like a spool with no differential action or difference in speed between the left and right wheels allowed.
More
www.offroaders.com/tech/limited-slip-lockers-differentials.htm
Standard/Open Carrier:
Whenever a vehicle negotiates a turn, the outside wheel must travel farther (turn faster) than the inside wheel. This is accomplished by spider gears that allow the outside wheel to turn faster (this can be either the left or the right, but must be the outside wheel) than the ring gear, while the inside wheel turns slower than the ring gear. The net sum of the speed of the two wheels is twice as fast as the ring gear. That means if the outside wheel is turning 2 rpm faster than the ring gear, the inside wheel is turning 2 rpm slower than the ring gear. This differential action is very straightforward in a standard open differential and works great for more than 95% of vehicles on the road today.
When a vehicle with an open or a standard differential encounters a loose traction surface, it directs power to the wheel with the least resistance. The resulting action is the wheel on the loose surface spins, while the opposite wheel on the better traction surface stands still or barely transfers power. The reason a standard open differential works this way is because it is designed to provide equal force to both sides. If the wheel on either side looses traction, the other side suffers as well.
If, for example, the left wheel looses traction and cannot provide a resistance force back to the differential side gear, then the right side gear cannot transfer a force to the right wheel to counteract the slipping left wheel. The main point to remember is that an open differential provides equal POWER to both sides, not equal speed.
An open differential works just fine for 95% of vehicles on the road, since most people do not spin their tires often, if at all. For those of us who like to burn rubber or go off the dry pavement, there are now too many limited slip and locking differentials to choose from.
Positractions & Limited Slips:
Posis and limited slips transmit equal torque to both wheels when driving straight. However, when one wheel spins due to loss of traction, a patch of ice, mud, too much throttle, etc., the unit automatically provides more torque to the wheel that has traction. Recommended for daily driving, works well in ice, rain, mud and snow. However, in situations where absolute lockup is needed, a limited slip is not the best choice due to the fact that limited slips do slip in some situations.
Positraction is a type of limited slip. The name "positraction" was used by General Motors for their limited slip differential and the name has been associated with limited slips for many years.
Automatic Lockers:
Lockers (mechanical locking differentials) provide 100% transfer of power to both drive wheels. This power can be lost if both wheels spin, but a locking differential will never let one wheel spin free by itself while the other one sits still (unless the unit is broken). Automatic locking differentials are engineered to keep both wheels in a constant drive mode, yet have the ability to unlock to permit a difference in wheel speed while negotiating turns.
Recommended for serious off-roaders or serious hot-rodders, they can be annoying for everyday driving. The main shortcoming of automatic lockers is the noise inherent in their design. When getting on or off the throttle, they tend to bang or clunk, or sometimes make noise while disengaging when negotiating a turn. These characteristics are due to the design and a few locker manufacturers have come up with designs that make less noise, but no one has developed a perfectly quiet automatic locker yet. One more effect of lockers that hampers every day use is that they only drive the inside wheel on a turn, which can affect vehicle handling.
When driving the inside wheel, the vehicle tends to yaw from side to side slightly when negotiating a turn under power. When turning sharply while taking off from a stop, the inside wheel will tend to spin easily. This is especially prominent when taking off on a right turn, for two reasons: the torque on the rearend housing due to the driveline torque un-weights the right wheel, and right hand turns are tighter (because we drive on the right side of the road).
On-Command Lockers:
Many people want the benefits of a locking differential, but do not want the handling characteristics or noise of an automatic locker. There are a few on-command lockers available as an OEM option. These include the 1998 and newer Toyota Tacoma and Land Cruiser. These EOM designs use an electric motor or vacuum diaphragm to engage the locker. When it is not engaged, the unit acts like a standard open differential with no ill side effects aside from poor traction. When engaged, these units' lockup 100% and act like a spool with no differential action or difference in speed between the left and right wheels allowed.
More
www.offroaders.com/tech/limited-slip-lockers-differentials.htm