Vishwakarma Institute of Technology, Pune, INDIA

ME-A BATCH 2 GROUP 1 – Guided by – Dr. Umesh Chavan.

GROUP MEMBERS 

Pranjali Bhople(Roll No-33)

Dinesh Bhor(Roll No-34)

Rutuja Bhosale(Roll No -35)

Vedant Bhosale(Roll No-36)

.DIFFERENTIAL GEAR BOX

WHAT IS A DIFFERENTIAL?

 A differential is a system that transmits an engines torque to the wheels. It takes the power from the engine and splits it, allowing the wheels to spin at different speeds.

A differential is a device that usually but not necessarily employ gears that are capable of transmitting torque and rotation through three shafts, almost always used in one of two ways:

•   In the first way, it receives one input and provides two outputs. It is found in most of the automobiles
• In the second way, it combines two inputs to create an output that is the sum, difference, or average, of the inputs.

Introduction

The differential gear is a part of the power transmission device. 

Differential gear in automotive mechanics, gear arrangement that permits power to be transmitted from the engine to a pair of driving wheels, divides the force equally between them but permitting them to follow paths of different lengths, as when turning a corner or traversing an uneven road.                     The differential gear assembly absorbs rotational differences due to the direction change of the rotational axis drive and/or the rotational differences between the right and left wheels that lead to smooth cornering.

• In automobiles and other wheeled vehicles, the differential gear allows each of the driving wheels to rotate at different speeds, while it seems to supply equal torque to each of them for most of the vehicles.  
• In vehicles without a differential, such as karts, both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a simple chain drive mechanism.

Differential gear box  

The different parts included in the gear box are:-

• 
  Pinion drive gear: transfers power from the drive shaft to the ring gear.
•  Ring gear: Transfers power to differential case assembly.
• Spider gear: This lies at the heart of differential and special mention should be made about its rotation.
•  Differential case assembly:  It holds the gear and drives the axle.
•  Rear drive axle:  It transfers torque from differential assembly to drive wheels.

  Working

The mechanism of a differential gear used in cars and other wheeled vehicles. Its work is to transmit power of engine in different ways to wheels equally but during turns it plays a vital role.  A differential allows the outer drive wheel to rotate faster than the inner drive wheel during a turn. This is necessary when a vehicle turns in order to allow the wheel that is traveling along the outside of the turning curve to roll faster and to cover greater distance than the wheel on the inside of the turning curve. 

    The average of the rotational speed of the two driving wheels is simply the input rotational speed of the drive shaft. An increase in the speed of one wheel is balanced by a decrease in the speed of the other. From the drive shaft power is transferred to pinion gear, since pinion and ring gear are meshed, power flows to the ring gear. As the spider gear is connected with the ring gear, power flows to it. And at last power from spider gear gets transferred to both side gears

Different Cases:             

•  The vehicle moves straight

In this case, the spider gear rotates along with the ring gear but does not rotate on its own axis. Therefore, the spider gear will push and make the side gear turn and both will turn at the same speed

•  The Vechicle takes a right turn

In this case, along with rotation of gear it rotates on its own axis. So, the spider gear has a combined rotation. When the spider gear is spinning as well as rotating, peripheral velocity at the left side of the spider gear is the sum of spinning and the rotational velocity. But on the right side it is the difference of two since the spin 

velocity is in the opposite direction.

Different Types

1.Open Differential 

This type of differential is the most basic and only allows for variations of individual wheel speed or slip but that’s it.  
       The most basic form comprises two halves of an axle with a gear on each end, connected together by a third gear making up three sides of a square. This is usually supplemented by a fourth gear for added strength, completing the square.
     

2.Limited-Slip Differential

    Under ideal road conditions, a limited-slip diff acts just like an open differential and transfers torque independently to each wheel. But, under hard cornering or heavy acceleration where an open differential would generally cause a tire to slip, a limited-slip diff prevents the normal amount of torque to go to the slipping tire (the one with least resistance).  

           It does so through the use of clutches and plates within the differential. This enables the vehicle to power through corners a vehicle with an open diff would struggle with. Race cars and other performance vehicles (as well as some off-road vehicles) use limited-slip differentials.

                              

3. Locking Differential

   

 The locked or locking differential is a variant found on some vehicles, primarily those that go off road and some performance cars. It uses clutches and spring to activate a lock. It is essentially an open differential with the ability to be locked in place to create a fixed axle instead of an independent one.

           

      The benefit of a locked differential is it is able to gain a considerably greater amount of traction than an open differential. Because the torque is not equally split 50/50 it can channel more torque to the wheel that has the better traction - and is not limited by the lower traction of the other wheel at any given moment.
     One disadvantage of locked diffs is called binding, which occurs when excess rotational energy (torque) is built up within the drive train and needs releasing – typically achieved by the wheels leaving the ground to reset the position. Or by simply releasing the locks once they are no longer needed.

4.WELDED/SPOOL DIFFERENTIAL

    Welded differentials are essentially the same as a locked differential, only it has been permanently welded from an open differential into a fixed axle (also known as a spool diff.) This is usually only done in specific circumstances where the characteristics of the locked diff/fixed axle, which makes it easier to keep both wheels spinning simultaneously, are desirable – for example, in cars meant for drifting.
          It's typically not recommended as the heat from welding can compromise component strength and increase the risk of catastrophic part failure - potentially even resulting in the broken differential gears exploding through the diff casing and posing a hazard to other road users and pedestrians.

 

5.TORSEN DIFFERENTIAL

 The Torsen (Torque – Sensing) differential employs the use of some clever gearing to produce the same effect as a limited Slip Differential without the need for clutches or fluid resistance. It achieves this by adding a layer of worm gearing to the traditional gear set up of an open differential. These sets of worm gears acting on each axle provide the resistance required to enable torque transfer, which it then achieves by having the worm gears in constant mesh with each other via connected spur gears.

6.Torque-Vectoring Differential

    Torque- Vector Differential is the most complicated and advanced type of differential, it uses a collection of sensors and electronics to obtain data from various things (road surface, throttle position, steering system, etc.) to activate electronically actuated clutches and a controller.

                    The TVD takes this electronically enhanced system even further by using it to manipulate the angle, or vector, of the vehicle in and out of the turns by encouraging specific wheels to receive more torque at key moments - improving cornering performance.

            They work in the most efficient way which results in a truly dynamic, high performance driving experience. Torque-vectoring differentials can be found in some high  performance rear-wheel drive and all-wheel drive vehicles.

Advantages

• In spite of large amount of power delivered from the transmission system the differential reduces the speed with respect to its movement in the right or left direction.
•   It turns the flow of power by 90 degrees.
• Allow the wheels to rotate at different speeds in turn.

Disadvantages

    Loss of  Traction:

One undesirable side effect of an open differential is that it can limit traction under less than ideal conditions. The amount of traction required to propel the vehicle at any given moment depends on the load at that instant—how heavy the vehicle is, how much drag and friction there is, the gradient of the road, the vehicle's momentum, and so on. 

                 Traction is defined as the amount of force that can be transmitted between the tire and the road surface before the wheel starts to slip. If the torque applied to one of the drive wheels exceeds the threshold of traction, then that wheel will spin, and thus provide torque only at the other driven wheel equal to the sliding friction at the slipping wheel. The reduced net traction may still be enough to propel the vehicle slowly.

Applications

•    Automotive

In automobiles and other wheeled vehicles, the differential allows the outer drive wheel to rotate faster than the inner drive wheel during a turn. This is necessary when the vehicle turns, making the wheel that is traveling around the outside of the turning curve roll farther and faster than the other.

 The average of the rotational speed of the two driving wheels equals the input rotational speed of the drive shaft. An increase in the speed of one wheel is balanced by a decrease in the speed of the other. When used in this way, a differential couples the longitudinal input propeller shaft to the pinion, which in turn drives the transverse ring gear of the differential. This also usually works as reduction gearing.

    On rear wheel drive vehicles the differential may connect to half-shafts inside an axle housing, or drive shafts that connect to the rear driving wheels. Front wheel drive vehicles tend to have the engine crankshaft and the gearbox shafts transverse, and with the pinion on the end of the counter-shaft of the gearbox and the differential enclosed in the same housing as the gearbox. There are individual drive-shafts to each wheel. A differential consists of one input (the drive shaft) and two outputs, which are connected to the two drive wheels; however the rotations of the drive wheels are coupled to each other by their connection to the roadway

    A vehicle with two drive wheels has the problem that when it turns a corner the drive wheels must rotate at different speeds to maintain traction. The automotive differential is designed to drive a pair of wheels while allowing them to rotate at different speeds. In vehicles without a differential, such as karts, both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a simple chain-drive mechanism.

     In rear-wheel drive automobiles the central drive shaft (or prop shaft) engages the differential through a hypoid gear (ring and pinion). The ring gear is mounted on the carrier of the planetary chain that forms the differential. This hypoid gear is a bevel gear that changes the direction of the drive rotation.

•      Non- Automotive

Non-automotive uses of differentials include performing analog arithmetic. Two of the differential's three shafts are made to rotate through angles that represent (are proportional to) two numbers, and the angle of the third shaft's rotation represents the sum or difference of the two input numbers.