Difference between revisions of "Differential"

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==Function of a Differential==
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A differential is a mechanism that allows the two driven wheels to rotate at different speeds to assist in cornering.
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When turning a corner, the outer wheels will follow a path with a greater radius of curvature. This difference in radius means the outside wheels will have tp travel a longer distance, and rotate faster than the inside wheels.in a rear wheel drive car, the frint two wheels are allowed to rotate at a different rate, so this does not pose a problem. The rear wheels, however, both have to be driven by the enginw, and therefore mechanically connected to eachother, so there is no freedom of movement between them inherent in the design.
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=Function=
 +
When turning a corner, the outer wheels will follow a path with a greater radius of curvature. This difference in radius means the outside wheels will have to travel a longer distance, and rotate faster than the inside wheels.in a rear wheel drive car, the front two wheels are allowed to rotate at a different rate, so this does not pose a problem. The rear wheels, however, both have to be driven by the engine, and therefore are mechanically connected to each other, so there is no freedom of movement between them inherent in the design.
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{{#evt:service=youtube|id=https://www.youtube.com/watch?v=yYAw79386WI}}
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=Limited Slip Differential=
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An open differential is a gear assembly that allows the two rear wheels to spin independently of each other, while maintaining the average rotational speed. If the outside wheel spins faster than it would without the differential, the inside wheel must spin and equivalent amount slower. Similarly, the torque transferred to the ground, but is split in varying amounts between the two rear wheels depending on their relative velocities. The faster spinning wheel will see a proportionally greater amount of torque from the engine.
  
 +
This torque differential between the two wheels can become problematic in high torque applications where the torque is desired to go to the wheel with the greatest amount of traction, not the greatest rotational velocity, such as corner exit, or corner entry if using an inboard brake. To solve this problem, a differential that can limit the amount of slip is desired.
  
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[need a pic of cornering to demonstrate wheel travel difference]
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A limited slip differential (LSD) allows the two wheels to rotate at different speeds, but is limited to a maximum difference. The maximum limit of torque sent to one side is the torque bias ratio (TBR) of the LSD.
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==Clutch==
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Clutch type LSDs are chosen primarily for their adjustability or availability now that Torsen no longer makes FSAE specific diffs. The clutch type diff can be adjusted to lock up at differing torques under acceleration and braking.
  
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Clutch type LSDs can be categorized by which direction they lock up in. If the differential will lock up under both braking and acceleration, it is called a 2-Way. If it locks up under only acceleration, it is called a 1-Way. If the differential does not lock up but allows less differential action than the TBR in one direction, and locks up in the other it is called a 1.5-Way.
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==Geared==
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Geared LSDs are sometimes referred to by the supplier: Torsen, Quaife, and Eaton. Geared LSDs rely on the geometry of gears to determine the TBR, so changing the TBR is much more difficult than on a clutch type differential. Gear type LSDs are often chosen for their longevity, low maintenance, and lack of energy loss inherent in clutch pack designs. [someone check me on this].
  
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A differential is a mechanism that allows the two driven wheels to rotate at different speeds to assist in cornering.
+
Torsen makes three versions<ref>The T-1 uses cross axis planetary helical and spur gears. The T-2 uses axial planetary helical gears. The T-3 is designed as a center differential for AWD OEM applications.</ref>. The company no longer sells FSAE/FS specific diffs but the data and information is kept available on their website.
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==Other Types==
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There are other types of limited slip differentials that are either not commonly used or simply unused in FSAE applications.
 +
* Locking
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** Detroit Locker
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** Cam and Pawl
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* Viscous
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* eLSD (may change as tech gets better)
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=Spool=
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Although not technically a differential, a spool does still transfer power from the engine to the wheels. A spool mechanically ties the two wheels together: they will always spin at the same speed. This can lead to massive understeer unless suspension is designed to compensate. To compensate, the inside rear wheel should be designed to be unweighted or even lift up off the ground in a corner. This can be achieved with the right suspension setup usually involving scrub, and a generous application of caster. The main advantage to using a spool is the weight savings and simplicity.
  
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=Electronic Differential=
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It is fairly common to find electric formulas where the [[battery pack]] powers more than one motor on each side of the car. These two motors are then controlled individually and behave like if a virtual electronic differential was separating each other.
  
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(written w dog on lap, lots of mechanical errors, sorry, will fix later if yall dont)
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=Differentials used in Formula=
  
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==Open Differential==
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{| class="wikitable"
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An open differential is a gear assembly that allows the two rear wheels to spin independently of each other, while maintaining the average rotational speed. If the outside wheel spins faster than it would without the differential, the inside wheel must spin and equivalent amount slower. Similarly, the torque transferred to the ground, but is split in varying amounts between the two rear wheels depending on their relative velocities. The faster spinning wheel will see a proportionally greater amount of torque from the engine.
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|-
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|Name
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|Type
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|TBR
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|Comments
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|-
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|[https://torsen.com/fsae/ Torsen University Special]
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|T-1 or T-2 Torsen LSD
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|2.6:1
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|obsolete
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|-
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|TRE mk1
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|
 +
|
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|obsolete
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|-
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|[https://www.taylor-race.com/catalog/1283 TRE mk2]
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|
 +
|
 +
|
 +
|-
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|[https://shop.drexler-motorsport.com/en/limited-slip-differential/formula-student/ Drexler]
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|Clutch pack
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|Adjustable
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|
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|-
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|Quaife
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|
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|
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|
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|}
  
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=Further Reading=
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* https://www.taylor-race.com/sites/default/files/DIFFERENTIAL%20ESSAY%20W%20PHOTOS2.pdf
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* [https://www.youtube.com/playlist?list=PL2ir4svMoaYim-RSNWEh-aIfdcM6plSly Engineering Explained:Differentials (Youtube Playlist)]
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* https://www.awdwiki.com/en/torsen/
  
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This torque differential between the two wheels can become problematic in high torque applications where the torque is desired to go to the wheel with the greatest amount of traction, not the greatest rotational velocity, such as corner exit, or corner entry if using an inboard brake. To solve this problem, a differential that can limit the amount of slip is desired.
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=References=
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<references />
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==Limited Slip Differential==
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<br />
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==Torque Vectoring==
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[[Category:Drivetrain]]
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[[Category:Internal Combustion]]
 
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[[Category:Electric Vehicle]]
 

Latest revision as of 00:15, 3 February 2023

A differential is a mechanism that allows the two driven wheels to rotate at different speeds to assist in cornering.

Function

When turning a corner, the outer wheels will follow a path with a greater radius of curvature. This difference in radius means the outside wheels will have to travel a longer distance, and rotate faster than the inside wheels.in a rear wheel drive car, the front two wheels are allowed to rotate at a different rate, so this does not pose a problem. The rear wheels, however, both have to be driven by the engine, and therefore are mechanically connected to each other, so there is no freedom of movement between them inherent in the design.

Limited Slip Differential

An open differential is a gear assembly that allows the two rear wheels to spin independently of each other, while maintaining the average rotational speed. If the outside wheel spins faster than it would without the differential, the inside wheel must spin and equivalent amount slower. Similarly, the torque transferred to the ground, but is split in varying amounts between the two rear wheels depending on their relative velocities. The faster spinning wheel will see a proportionally greater amount of torque from the engine.

This torque differential between the two wheels can become problematic in high torque applications where the torque is desired to go to the wheel with the greatest amount of traction, not the greatest rotational velocity, such as corner exit, or corner entry if using an inboard brake. To solve this problem, a differential that can limit the amount of slip is desired.

A limited slip differential (LSD) allows the two wheels to rotate at different speeds, but is limited to a maximum difference. The maximum limit of torque sent to one side is the torque bias ratio (TBR) of the LSD.

Clutch

Clutch type LSDs are chosen primarily for their adjustability or availability now that Torsen no longer makes FSAE specific diffs. The clutch type diff can be adjusted to lock up at differing torques under acceleration and braking.

Clutch type LSDs can be categorized by which direction they lock up in. If the differential will lock up under both braking and acceleration, it is called a 2-Way. If it locks up under only acceleration, it is called a 1-Way. If the differential does not lock up but allows less differential action than the TBR in one direction, and locks up in the other it is called a 1.5-Way.

Geared

Geared LSDs are sometimes referred to by the supplier: Torsen, Quaife, and Eaton. Geared LSDs rely on the geometry of gears to determine the TBR, so changing the TBR is much more difficult than on a clutch type differential. Gear type LSDs are often chosen for their longevity, low maintenance, and lack of energy loss inherent in clutch pack designs. [someone check me on this].

Torsen makes three versions[1]. The company no longer sells FSAE/FS specific diffs but the data and information is kept available on their website.

Other Types

There are other types of limited slip differentials that are either not commonly used or simply unused in FSAE applications.

  • Locking
    • Detroit Locker
    • Cam and Pawl
  • Viscous
  • eLSD (may change as tech gets better)

Spool

Although not technically a differential, a spool does still transfer power from the engine to the wheels. A spool mechanically ties the two wheels together: they will always spin at the same speed. This can lead to massive understeer unless suspension is designed to compensate. To compensate, the inside rear wheel should be designed to be unweighted or even lift up off the ground in a corner. This can be achieved with the right suspension setup usually involving scrub, and a generous application of caster. The main advantage to using a spool is the weight savings and simplicity.

Electronic Differential

It is fairly common to find electric formulas where the battery pack powers more than one motor on each side of the car. These two motors are then controlled individually and behave like if a virtual electronic differential was separating each other.

Differentials used in Formula

Name Type TBR Comments
Torsen University Special T-1 or T-2 Torsen LSD 2.6:1 obsolete
TRE mk1 obsolete
TRE mk2
Drexler Clutch pack Adjustable
Quaife

Further Reading

References

  1. ↑ The T-1 uses cross axis planetary helical and spur gears. The T-2 uses axial planetary helical gears. The T-3 is designed as a center differential for AWD OEM applications.


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