## Differential – A hidden wonder of automobile

While driving a car have you ever wondered how does the engine drive the wheels? How only one engine drives all the wheels of the car? How does the system manage to transmit the power to the wheels? Let’s have a brief look under the hood and understand a very important concept of an automobile, that is “DIFFERENTIAL”.

Engineering of an automobile is a very vast subject. On an average, about 30,000 parts are used for the manufacturing of a single car. Hence to study automobile, the whole subject is divided into 6 major systems: Chassis, Engine, Transmission, Steering, Braking, Suspension. Differential is a part of Transmission system.

Main aim of transmission, as the name suggests is to transmit the power produced by the engine to the wheels so that the vehicle moves. A transmission in general consists of an input shaft, an output shaft, gears and a differential. The input shaft gets power directly from the engine, which is manipulated according to our needs by gears and finally the output shaft carries the final power.

The differential then comes into action. The differential transmits the the power produced by the output shaft sideways.

As shown in the picture, the differential is situated between the two wheels and it transfers the motion of transmission shaft/output shaft to the rotary motion of the wheels. The transmission shaft rotates the driving pinion, which in turn drives the ring gear (crown wheel). This ring gear is attached to a small sun gear/side gear. This side gear is meshed via the differential pinion gear(planet gear). Both the side gears are connected to the half shafts(axle) connected to the wheels.

Why to use the side gears pinion assembly when we can directly connect the ring gear? Also this work seems to be easy. But this is not all a differential does. A differential is designed for a far more greater purpose.

Whenever an automobile turns, there is a difference in the speeds of the inner and the outer wheels.

As you can see, the outer wheel of the automobile has to travel a larger distance than the inner wheel in the same amount of time while turning. Hence the speed of outer wheel is more. This can be achieved by unequal and proportionate distribution of power to the wheels. The outer wheel needs more power than the inner wheel and this unequal but proportionate distribution of power is done by the differential.

The inner half shaft in the figure indicated the part of the shaft connected to the inner wheel while the outer half shaft to the outer wheel. Both the shaft move in anticlockwise direction when moving on a straight road. Hence the power is distributed equally and both the side gears hence the shaft rotate at same speed.

While turning, both shafts do rotate in the same direction. The outer wheel has to move at higher speed than the inner wheel. This produces a couple moment at the differential pinion. This force drives the pinion gear to rotate. Due to this rotation, the side gear of the outer shaft rotates at a rate higher than the inner wheel. The side gear of outer shaft gets an additive rpm while the inner shaft gets a subtractive rpm. Hence due to this production of different speeds in both the wheels, the system is called a differential.

Hence for different turns, different torque is applied on the differential pinion and according powers are provided to the wheels. This was the basic information about differential and transmission. Further the differentials are classified into different types differentials like open differential, locking differential, limited slip differential, electronically controlled limited slip differential, torque vectoring differential etc. But for basic understanding of the differential, this much knowledge is enough.

## Visit at Volkswagen Plant, Pune

“Why only Volkswagen can build a Volkswagen?”

This is cool line, but you know what’s cooler? The fact that it’s true.

What you can do just after the exams? Just follow CEV group activities and you will definitely find some great attraction towards CEV group and its activities. We thought to visit something really cool or by which we can enrich our Technical knowledge as well as can have fun with Techies.

We started our journey to visit Volkswagen Pune plant from SVNIT-Surat on the morning of Dec  7th,2014 for Mumbai. After reaching at BCT-Mumbai at 04:00pm, we visited some of the well-known places in Mumbai viz. Gate way of India, Hotel Taj, Churni road-Chopati till 09:00 pm. By the late night of Dec 7th, we reached at Pune and stayed at Hotel. As we were supposed to reach at company plant by 09:30am on Dec 8th, we fresh up early and went there by Tempo Traveller that we have hired. We started our best part of the journey at 10:00am, after the introductory session that has taken by Chaitanya Halbe sir. Here is the journey into one of the biggest and most respected carmakers. A great deal of Thought , Attention and Innovation goes into the every stage-process to built each car that is truly Das Auto ( The Car ).

As we all know, Cars can be divided into two groups according to their designs.

1. Hatch back
2. Siddan

Volkswagen worldwide

Volkswagen Automobile Group is globally represented by twelve brands- Volkswagen, Passenger Cars, Audi, SEAT, SKODA, Bentley, Bugatti, Lamborghini, Porsche, Ducati, Volkswagen Commercial Vehicles, Scania and MAN. The product spectrum ranges from motorcycles to luxury vehicles and heavy trucks.

Total production plants- 106 across 27 countries.

Total employees- 572,800 (including indirect employees)

The Volkswagen India plant, situated in the industrial hub of Pune i.e. Chakan -37 km away from Pune city, is one of the most modern facilities in the Volkswagen Group worldwide and has a high level of vertical integration. An initial investment commitment of Volkswagen group is INR 3,800 crores (580 million Euros) and is planning to invest INR 5000 crores more in upcoming years.

The state-of-the-art Pune Plant builds Volkswagen Polo and Vento and SKODA Rapid on a single line at the same time.

Employees- 3,600 (including 1,100 indirect employees and 33 R&D researchers)

Total Area- 575 acres (including 100 acres constructed area)

Investment till date- 700 million Euros

Production of cars per day- 430 cars in 2 shifts

Production Capacity- 130,000 cars in 2 shifts

Cars Produced

1. Volkswagen Polo since Dec 2009 (Right Hand Drive as well as Left Hand Drive)
2. Volkswagen Vento since Aug 2010 (Right Hand Drive as well as Left Hand Drive)
3. SKODA Rapid since Oct 2011 (Right Hand Drive Only)
4. SKODA Fabia till Dec 2013 only

The manufacturing facility includes Body Shop followed by

Paint Shop and then

Assembly line

1. Body Shop – Initial stage where car starts taking shape.

Pressed metal (100% Galvanised steel for 100% strength & safety) parts from the Press Shop are received in the Body Shop to create the body shell.

The car bodies are built from bottom to top; starting from the underbody, then the side framers, roof and finally with closure parts viz. doors, bonnet and boot lid with almost 35% of automation.

1. Paint Shop – Stage in which car is giving its colours

Firstly, the vehicle body undergoes a cleaning process after which it gets the ElectroCoat followed by Coarse Sealent, Underbody Coating and Fine Sealing before getting the Primer Coat.

Finally, finishing and waxing of the body is done and then car body is sent to the assembly line.

Local manufacturers – Asian Paints. (To decrease the manufacturing cost)

1. Assembly line – Final area of manufacturing

Here, you’ll get a chance to experience German Engineering, made in India. Also, witness one of the fastest marriages of Chassis with remaining car body. The car then moves to the finish line where it gets the steering wheel, airbags, seats and doors.

Local manufacturers – MRF and Apollo for tyres.

Why should you buy Volkswagen cars?

1. Unique Roof Laser Welding for greater rigidity and zero dampness. (Roof stay stronger and more secure even after years.)
2. 6 years of anti-perfurism warranty
3. Inline Measurement process done by Robots for zero-error body that lasts years.
4. 11-stage Paint Process for longer-lasting beauty and Ro-Dip Technology for 360* paint coverage for excellent corrosion protection.

Extra tests carried out on Volkswagen cars

1. Stone Impact Test to check paint and body strength.
2. Destruction Tests to ensure ultimate endurance & quality.
3. Intense checks for almost 7 hours on each car.
4. Test on special track.

Exports from Pune Plant

‘German Engineering, Made in India by Volkswagen’ is in great demand worldwide. Currently, Volkswagen India exports the Polo and Vento, in right-hand as well as left-hand drive versions, to over 32 countries across three continents – Asia, Africa and North America.

Commencement of export – 2011 in South Africa

2012 in Middle East countries with LHD

2013 in Mexican Market with Indian Vento

2013 in Malaysia with component of Polo and Vento

CEVians really enjoyed the manufacturing process of POLO and its elder brother Vento and the iconic distinct cousin Beetle.

## Flow Boiling

Boiling

Boiling is classified as pool boiling or flow boiling, depending on the presence of bulk fluid motion.

Pool Boiling and Flow Boiling

• Boiling is called pool boiling in the absence of bulk fluid flow and flow boiling (or forced convection boiling) in the presence of it. In flow boiling, the fluid is forced to move in a heated pipe or over a surface by external means such as a pump or from height. Therefore, flow boiling is always accompanied by other convection effects.

Sub-cooled Boiling and Saturated Boiling

        Boiling is said to be sub cooled (or local) when the temperature of the main body of the liquid is below the saturation temperature Tsat (i.e., the bulk of the liquid is sub cooled) and saturated (or bulk) when the temperature of the liquid is equal to Tsat (i.e., the bulk of the liquid is satu

Void fraction in a Gas-Liquid Flow

        The fraction of the channel volume that is occupied by the gas phase.

        The fraction of the channel cross-sectional area that is occupied by the gas phase.

        Quality Profile :-  Vapour Quality is the percentage of mass in a saturated mixture that is vapour i.e. saturated vapour has a “quality” of 100%, and saturated liquid has a “quality” of 0%.

APPLICATIONS

  This type of boiling take place in Nuclear reactors and Aerospace Engines.

  Flow boiling is also used in the cooling of Electronic Circuit Boards using Micro channels.

  All the refrigeration cycles are based on flow boiling.

  Cooling systems in various industries comprise of Flow boiling.

## Application Of Electronics in Automobiles

APPLICATION OF ELECTRONICS IN AUTOMOBILES

Automotive electronics or automotive embedded systems are distributed systems and according to different domains in the automotive field they can be classified into:

}        Engine Electronics

}        Transmission Electronics

}        Chassis Electronics

}        Active Safety

}        Driver assistance

}        Passenger Comfort

}        Infotainment systems

Engine Electronics

}        One of the most demanding electronic part of an automobile is the engine control unit. Engine controls demand one of the highest real time deadlines, as the engine itself is very fast and complex part of the automobile. Of all the electronics in any car the computing power of the engine control unit is the highest, typically a 32-bit processor.

In a Diesel Engine

}        -Fuel injection rate

}        -Emission control, Nox control

}        -Regeneration of oxidation catalytic converter

}        -Turbocharger control

}        -Cooling system control

}        -Throttle control

In a Gasoline engine

}        OBD OnBoard diagnosis

}        -Cooling system control

}        -Ignition system control

}        -Lubrication system control (only few has electronic control)

}        -Fuel injection rate control

}        -Throttle control

Transmission Electronics

}        This controls the transmission system; mainly it controls the shifting process of the gears. For a better shift comfort, lower torque interrupt while shafting -these electronics are used in a manual transmission. Many semi automatic transmissions which have a fully automatic clutch or a semi-auto clutch (only declutching) use electronics for its operation and control. Also fully automatic transmissions use controls for their operation.

Chassis Electronics

}        ABS – Anti-lock braking system

}        TC – Traction control system

}        EBD – Electronic brake distribution

}        ESP – Electronic Stability Program

Active Safety

}        Air Bags

}        Hill Descent Control

}        Emergency Brake assist system

Driver assistance

}        Lane assist system

}        Speed assist system

}        Blind spot detection

}        Park assist System

Passenger Comfort

}        Automatic Climate control

}        Electronic seat adjustment with memory

}        Automatic wipers

Infotainmentems

}        Music system

Information access

CEV - Handout