D(if)ferential

Published by Nayan on

One of the mechanical marvels from Driveline family running towards its extinction is Differential. The development of individual drive systems for all wheels has put a big question mark on the applicability of the differential.

Before the differential loses this race of evolution Lets find out what the device does and how it evolved?

Also, check out the blogs about the Wheels and tires:

Wheel-o-city

Introduction

Automobiles without differential- TurboTextBlog

  • With the evolution of automobiles, the power transmission took place through a single wheel but the model was soon discarded as the complete vehicle came to a halt when the power transmitting wheel got stuck and there was no way to get the vehicle moving again.
  • Soon the concept was replaced with front and rear drives where either front or rear wheels received transmission power but this model also had some shortcomings.
  • The word differential means based on difference and here we used it for the relative speed of both the wheels.

Principle

differential working Principle-TurboTextBlog

  • While taking a turn, the outer wheels have to travel greater distance as compared to inner wheels in same time. The differential is a device that allows driving a pair of wheels with the same force but allows them to rotate at different speeds.

Open differential

Open Differential-TurboTextBlog

  • Drive shaft- Torque is Supplied from engine, via transmission to the final drive unit which contains differential.
  • Bevel pinion- It transmits the torque from drive shaft to the final drive unit and meshes to the crown Wheel.
  • Sun gear- when one sun gear rotates it causes the other sun gear to rotate in opposite direction.
  • Crown Wheel- it is attached to the cage. It is free to rotate on one of the half shafts. It carries the spider.
  • Planet Gears- it imparts the motion of the crown wheel and sun gear to the other sun gear by pushing it instead of turning it as planet gear are not restricted from rotating against each other. They act as a balance and divide torque equally between two wheels on the axle.

Application

  • Where performance and off-road capabilities are not required.
  • MiniVan
  • Crossovers
  • Economy sedans

Loss of traction

Loss of Traction-TurboTextBlog

  • The torque applied to each driving wheel is a result of the engine and transmission applying the twisting force against the resistance of traction at the road wheel.
  • Due to this if one wheel is on a slippery surface it can simply skid and all the generated torque would rotate it idly and the opposite wheel will remain stationary.
  • This is a result of the lack of friction in the differential system.

LOCKING DIFFERENTIAL

Locking Differential-TurboTextBlog

  • A locking differential is a variation on the standard automotive differential.
  • It is designed to overcome the chief limitation of a standard open differential by essentially “locking” both wheels on an axle together as if on a common shaft.
  • This forces both wheels to turn in unison, regardless of the traction available to either wheel individually.
  • In case of Open differential (FIG BELOW TOP), it always provides the same torque (rotational force) to each of the two wheels, on that axle. This means {Equal torque, Unequal rotational speed.
  • Whereas in the case of Locking differential, it forces both the left and right wheels on the same axle to rotate at the same speed under nearly all circumstances. This means {Unequal torque, Equal rotational speeds}

TYPES OF LOCKING DIFFERENTIAL

  • AUTOMATIC SYSTEMS- It locks & unlock automatically without any input from the driver. Engine power is always transmitted to the wheels irrespective of traction condition & unlock only when one wheel has to spin faster than other(Cornering).E.g- General motors Gov-Lok.
  • SELECTABLE SYSTEMS- It allows the driver to lock unlock as desired. It is achieved by compressed air or solenoids. These are more complex and expensive.

EGERODISC DIFFERENTIAL

Egerodisc Differential-TurboTextBlog

  • In this type of differential, a gear rotor pump supplies hydraulic pressure under differential action.
  • A pressure regulating valve modulates the pressure applied to the piston to compress clutch pack to give desired torque.
  • Its advantages are it provides full axle lock, torque can be modulated from 0 to 100% as well as its compatibility with ABS.

ELOCKER DIFFERENTIAL

Elocker Differential- TurboTextBlog

  • This type of differential is operated electrically.
  • An electromagnetic coil activates the ball ramp engaging case to gear producing 100% lock.
  • It is compatible with ABS and VES(Vehicle Stability Control Systems)
Application
  • Jeep Wrangler
  • Mercedes-Benz g-class
  • Optional on full-size trucks
Limitation
  • Behaves like an open differential when not locked. Locking the diff on a high-grip surface such as dry pavement makes it difficult to turn the vehicle and can grenade the driveline.

Types of LSD

CLUTCH TYPE LSD

Clutch type Limited Slip Differential(LSD)-TurboTextBlog

The clutch type LSD has all of the same components as an open differential, but it adds a spring pack and a set of clutches. Some of these use flat disc clutches while others use a cone clutch similar to a synchronizer in a manual transmission. In the picture here you can see a central spring pack and clutch discs outboard of the sun gears.

 

Clutch type Limited Slip Differential(LSD)-TurboTextBlog

VISCOUS COUPLING TYPE LSD

  • The viscous coupling has two sets of plates inside a sealed housing that is filled with a thick fluid.
  • One set of plates is connected to each output shaft. Under normal conditions, both sets of plates and the viscous fluid spin at the same speed.
  • When one set of wheels tries to spin faster, perhaps because it is slipping, the set of plates corresponding to those wheels spins faster than the other.
  • The viscous fluid, stuck between the plates, tries to catch up with the faster disks, dragging the slower disks along.
  • This transfers more torque to the slower moving wheels — the wheels that are not slipping.

Viscous Coupling type LSD-TurboTextBlog

Electronic LSD

  • In place of a mechanical LSD, an electronic LSD consists of a conventional differential and an extension to the car’s electronic stability system.
  • Instead of transferring torque to the outside wheel while cornering, the system does the reverse, limiting torque to the inside wheel by applying brake force to it. This also has the effect of inducing the differential to transmit power to the opposite side.

GEROTOR LSD

Grotor Type LSD-TurbpTextBlog

  • Gerodisc differentials are speed sensitive slip-limiting differential units.  They contain a clutch pack and a hydraulic pump.
  • The pump is the gerotor type, whose pressure output depends upon rotational speed.
  • An axle shaft drives the pump; therefore the output from the pump depends on the speed of the axle.
  • When one wheel spins faster than the other, the pump’s speed and output pressure increases. The fluid then works on the clutch pack at the wheel with the most traction.
  • The amount of torque transfer is determined by the amount of pressure applied to the clutch pack.
  • When an axle is not slipping, the pump does not deliver pressure and the differential functions as an open unit.
Applications
  • Nissan 370Z with sports package (viscous)
  • Mazda MX-5 (Clutch type)
  • Subaru BRZ (helical)

No Differential!

VW Isetta- TurboTextBlog

  • Drag Racers
  • Light vehicles with closely spaced rear wheels
  • Vehicles with separate motors driving each wheel. Electric cars.
  • Three wheelers

I hope the post gives you a clarity on the working and types of differentials. You can also check out more blogs on Opiniontechnical, and Formula one.

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8 Comments

Kaushal Kumar upadhyay · September 5, 2018 at 4:33 pm

Nice good

    Nayan · October 11, 2018 at 2:18 pm

    Thank You so much. Stay tuned for the next one. 🙂 🙂

meenakshi · September 14, 2018 at 10:34 am

hi Nayan

You’re doing well, nice and unique website

    Nayan · October 11, 2018 at 2:04 pm

    Thank You so much. Stay tuned for the next one. 🙂 🙂

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    Nayan · January 17, 2019 at 4:20 am

    Thank you 🙂 🙂 🙂
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    Nayan · January 17, 2019 at 4:12 am

    Thank you 🙂 🙂 🙂
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