What is a Differential Gear Box?

            What is a Differential Gear Box?

 While travelling in a car, on a hard turn inside and outside wheels have different   velocities, not just the direction but magnitude also - even after being connected to   the same axle. But how ? Well, after reading this blog I’m pretty sure you’ll   understand this beautiful and simple creation of mechanical engineering.

        FIRSTLY, WHAT IS THIS THING AND WHAT IT DOES?

So, a differential is a device, usually but not necessarily employing gears, capable of transmitting torque and rotation through three shafts, almost always used in one of two ways: in one way, it receives one input and provides two outputs this is found in most automobiles and in the other way, it combines two inputs to create an output that is the sum, difference, or average, of the inputs. In automobiles and other wheeled vehicles, the differential allows each of the driving road wheels to rotate at different speeds, while for most vehicles supplying equal torque to each of them. A vehicle's wheels rotate at different speeds, mainly when turning corners. The differential is designed to drive a pair of wheels with equal torque 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. When cornering, the inner wheel needs to travel a shorter distance than the outer wheel, so with no differential, the result is the inner wheel spinning and/or the outer wheel dragging, and this results in difficult and unpredictable handling, damage to tires and roads, and strain on (or possible failure of) the entire drive train.

       NOW, THIS DEVICE IS MADE OF MANY GEARS…

First one is the Pinion gear : It’s function is to transfer power from the drive shaft to the ring gear. Second one is the Ring Gear : It contributes by transferring power to differential case assembly. Next one is the Spider Gear : This gear lies at the heart of the differential. Fourth one is the huge Differential Case Assembly : It basically holds the gear and the drive axle. And last part is the Rear Drive Axle: Its main function is to transfer the torque from the differential assembly to the drive wheels.

       IT HAS MANY FUNCTIONS, BUT IN A VEHICLE…

1. It transmits the power from the engine to the wheels,
2. It Changes the direction of rotation by 90 degrees,
3. It acts as the final gear reduction in the vehicle, showing the rotational speed of the transmission one final time before it hits the wheels and
4. It splits the engine torque into two ways, allowing each output to spin at a different speed. (This is the one that earned the differential its name.)

But how does it actually work inside the vehicle? Remember the question I asked at the starting? Now you’ll surely get it.

Wheels receive power from the engine via a drive shaft. The wheels receive power and make the vehicle move forward are called the drive wheels. The main function of the differential gear is to allow the drive wheels to turn at the different rpms while both receiving power from the engine.

Consider these wheels, which are negotiating a turn. It is clear that the left wheel has to travel a greater distance compared to the right wheel. This means that the left wheel has to rotate at a higher speed compared to the right wheel.

If these wheels were connected using a solid shaft, the wheels would have to slip to accomplish the turn. This is exactly where a differential comes in handy. The ingenious mechanism in a differential allows the left and right wheels to turn at different rpms, while transferring power power to both wheels.

NOW THERE ARE MAINLY TWO CASES : FIRST ONE IS WHEN THE VEHICLE IS MOVING STRAIGHT AND OTHER IS WHEN IT TAKES A TURN…

 

In this first case when it moves straight, the spider gear rotates along with the ring gear but does not rotate on its own axis.

So, the spider gear will push and make the side gears turn, and both will turn at the same speed.

In the second case, while taking a turn what happens is along with the rotation of the ring gear, it rotates on its own axis.

So, the spider gear is having a combined rotation.

When the spider gear is spinning as well as rotating, peripheral velocity at the left side of spider gear is the sum of the spinning and rotational velocity.

But at the right side, it is the difference of the two, since the spin velocity is in the opposite direction at this side.

 

      ONCE AGAIN KEEP THIS POINT IN MIND…

 

From the drive shaft power is transferred to the pinion gear first, since the 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.

Finally from the spider gear, power gets transferred to both the side gears.

 

     IT HAS SOME OTHER FUNCTIONALITIES TOO…

 

 1)          First is speed reduction at the pinion-ring gear assembly. Since, the power flow at the pinion and ring gear are the same, such a speed reduction will result in a high torque multiplication.

 2)          It can also note one speciality of the ring gear, they are hypoid gears. Hypoid gears have more contact area compared to the gear pairs.

 3)          It can be used to turn the power flow direction by 90 degrees.

 4)          And at last for speed reduction at the pinion-ring gear assembly, ring gear has 4-5 times teeth as that in pinion gear.

 

    NOW IT HAS SOME LIMITATIONS AND SO THERE ARE MANY      OTHER TYPES OF DIFFERENTIALS…

 

 1)          Open Differential

 2)          Locking Differential

 3)          Active/Electronic Differential

 4)          Limited-Slip Differential (LSD)

We’ve already studied Open Differential, let’s learn a bit more about the other types of differentials. First one is the Locking Differential.

                              LOCKING DIFFERENTIAL

 

These are used to achieve different torques at wheels of the same axle.

Locking means joining the two independent pinion gear. Application includes race car and off-road vehicles and 4 wheel drive.

To provide increased traction compared to normal Differential units.

When one rear axle wheel is stuck in the mud, 1. Open Differential will concentrate on rotating the stuck wheel while 2. Locked Differential will push the vehicle with the help of torque available at the free wheel.

Next one is the

                    ACTIVE OR ELECTRONIC DIFFERENTIAL

This dynamically locks the Differential using Electromagnetic Clutch.When cornering, the inner and outer wheels rotate at different speeds, because the inner wheels describe a smaller turning radius.The electronic differential uses the steering wheel command signal and the motor speed signals to control the power to each wheel so that all wheels are supplied with the torque they need. 

Next and the last one is 

              LIMITED SLIP DIFFERENTIALS OR LSDs

A LSD is very similar to the open Differential unit but has additional link that prevents wheel spin and loss of traction.

The standard differential delivers maximum torque to the wheel with minimum traction.

The limited slip differential delivers maximum torque to the wheel with maximum traction.

If the side gear encounters resistance, the planet gear rotates about the left side gear, in turn applying extra rotation to the right gear.

NOW THERE ARE ALSO THREE DIFFERENT TYPES OF LSDs, LET’S SEE THEIR NAMES AT LEAST…

1)     Clutch Pack

2)     Cone Clutch

3)     Torsen

These are 3 types of LSDs 

AT LAST, WHAT ARE THE LIMITATIONS OF THE FIRST ONE OPEN DIFFERENTIAL THAT WE’VE TO GET SOME MODIFICATIONS DONE?

The Differential we've studied at the start was Open Differential. Now consider a situation where one wheel of the vehicle is on a surface with good traction and the other wheel on a slippery track.

In this case, the majority of power will be sent to the slippery wheel and so the wheel is not able to move.

Also, this Differential always tries to balance the torque. Almost no torque is needed to spin one wheel and since it always sends the same amount of torque to both shafts.

                                             CONCLUSION

 So, I hope you all have understood much about this Differential gear box and what’s inside it. Thank you very much for giving this precious time of yours.

Authors: Arya Kokare, Piyush Kolhatkar , Akshay Khubchandani , Shreyash Khandwe,Harsh Khandelwal,Vaibhav Khandagle

Thank you for giving your time to read this and we hope you’ve got to know something more and something interesting today…………………………………...