What is LSD?
The limitations in differential is overcome by using Limited Slip Differential (LSD). It is a mechanical differential gear system used in automobiles to limit the relative motion between the wheels.
In a car with the conventional differential, if only one wheel is stuck on a slippery surface, then one wheel will be slipping freely over the slippery surface while the other wheel motion ceases. Limited Slip Differential overcomes it by transferring more torque to the non slipping wheel. This helps the vehicle escape a ditch easily.
LSD Construction:
One of the most commonly used technology for LSD is clutch pack based. The differential case has the same components that are used in a conventional differential. A pinion from the propeller shaft meshed to the ring gear, allowing 90 degree power transfer. The sun gears and planet gears are also meshed with each other. Planet gears rotate around the axis of the ring gear and also in its own axis. The sun gears are connected to the 2 half output shafts connected to each wheel. It has a series of friction and steel plates arranged alternately and packed together on either side between the sun gears and the differential case. There is a pre-load spring fitted between the sun gears.
LSD Working:
Friction discs are locked with the sun gears. Therefore, friction discs and side gear will always rotate together. Steel plates have external teeth and are made to fit in the grooves provided in the differential casing. Therefore, both steel plates and case rotate together.
If the clutch assembly is well pressed, then the entire clutch and case assembly will move together. Therefore, motion from the case is directly transferred to the half output shafts. The pre-load spring fitted between the sun gears will provide a side thrust and press the clutch discs together.
The sun and planet gear assembly is a bevel gear assembly. In a bevel gear system, axial forces are also induced apart from tangential forces. The axial force tries to push the sun gears against meshing with the planet gears. In the differential casing, a small allowance is provided to the sun gears for axial movement. Therefore, during high torque transfer, there is a huge amount of axial force acting on the sun gears that push it outwards towards the clutch pack. This axial thrust presses the clutch discs against the wall of the casing.
Vehicle with one wheel on a slippery surface:
Lets consider the case where one wheel is on slippery surface and the other is on a non slippery surface. Due to higher traction on the non slippery surface, the torque transferred towards the non slipping wheel will be higher. As a result, more axial thrust is created on the non slippery side and the clutch assembly on that side is locked. So power from the transmission is transmitted directly towards the non slippery surface via the clutch pack assembly.
On the slippery side, the axial force is not enough to lock the clutch pack. Therefore, power flow towards the slippery side is limited. As a result, the vehicle will overcome the traction difference problem.
While taking a turn:
While taking a turn, the LSD acts as a normal differential. In this case, the clutch pack won't come to use as the axial force developed will be less. As a result, the left and right wheels will turn at different speeds just like the conventional differential.
The limitations in differential is overcome by using Limited Slip Differential (LSD). It is a mechanical differential gear system used in automobiles to limit the relative motion between the wheels.
In a car with the conventional differential, if only one wheel is stuck on a slippery surface, then one wheel will be slipping freely over the slippery surface while the other wheel motion ceases. Limited Slip Differential overcomes it by transferring more torque to the non slipping wheel. This helps the vehicle escape a ditch easily.
LSD Construction:
One of the most commonly used technology for LSD is clutch pack based. The differential case has the same components that are used in a conventional differential. A pinion from the propeller shaft meshed to the ring gear, allowing 90 degree power transfer. The sun gears and planet gears are also meshed with each other. Planet gears rotate around the axis of the ring gear and also in its own axis. The sun gears are connected to the 2 half output shafts connected to each wheel. It has a series of friction and steel plates arranged alternately and packed together on either side between the sun gears and the differential case. There is a pre-load spring fitted between the sun gears.
LSD Working:
Friction discs are locked with the sun gears. Therefore, friction discs and side gear will always rotate together. Steel plates have external teeth and are made to fit in the grooves provided in the differential casing. Therefore, both steel plates and case rotate together.
If the clutch assembly is well pressed, then the entire clutch and case assembly will move together. Therefore, motion from the case is directly transferred to the half output shafts. The pre-load spring fitted between the sun gears will provide a side thrust and press the clutch discs together.
The sun and planet gear assembly is a bevel gear assembly. In a bevel gear system, axial forces are also induced apart from tangential forces. The axial force tries to push the sun gears against meshing with the planet gears. In the differential casing, a small allowance is provided to the sun gears for axial movement. Therefore, during high torque transfer, there is a huge amount of axial force acting on the sun gears that push it outwards towards the clutch pack. This axial thrust presses the clutch discs against the wall of the casing.
Vehicle with one wheel on a slippery surface:
Lets consider the case where one wheel is on slippery surface and the other is on a non slippery surface. Due to higher traction on the non slippery surface, the torque transferred towards the non slipping wheel will be higher. As a result, more axial thrust is created on the non slippery side and the clutch assembly on that side is locked. So power from the transmission is transmitted directly towards the non slippery surface via the clutch pack assembly.
On the slippery side, the axial force is not enough to lock the clutch pack. Therefore, power flow towards the slippery side is limited. As a result, the vehicle will overcome the traction difference problem.
While taking a turn:
While taking a turn, the LSD acts as a normal differential. In this case, the clutch pack won't come to use as the axial force developed will be less. As a result, the left and right wheels will turn at different speeds just like the conventional differential.
[…] technology improves its accuracy. Electronic limited slip differential (eLSD) is just like a normal LSD having pressurized hydraulic clutches, fine tuned with […]
ReplyDelete[…] Slip Differential houses a set of complicated gear system, but is the most effective of all the LSDs. This product is the trademark of the JTEKT corporation. Torsen was first patented by Gleasman in […]
ReplyDelete