A case study of the Tesla Model S

The transportation sector has contributed significantly to the increase in CO2 emissions worldwide. Automotive companies rely heavily on fossil fuel technologies. Due to the environmental constraints imposed by governments and the upcoming depletion of oil reserves, car manufacturers seek to implement new environmentally friendly technologies in their products. Electric vehicles are often described as the most feasible solution. Electric vehicles run on electricity and are powered by electric motors instead of internal combustion engines. The popularity of electric vehicles is growing since they produce zero emissions and little to no noise pollution, unlike fossil fuel-powered cars. In 1834, a Dutch professor Sibrandus Stratingh built his small electric vehicle made of non-rechargeable power cells. In the field of electric cars, Tesla kickstarted a revolution in the automobile industry in 2008 by launching the Roadster model. In continuation, they launched Model S in 2012 and Model X in 2014. Tesla spends a huge capital on research and development which makes it special to others. In 2006, when the co-founder and current CEO of Tesla Motors Elon Musk was asked about their strategy and stated:

“The starting point is a high-performance sports car, but the long-term vision is to build cars of all kinds, including low-cost family vehicles”.

Let's take a closer look at how these eco-friendly cars work—

Electric cars work on the principle of transforming electric energy into mechanical energy – from which kinetic energy is obtained. These cars use the energy stored in their rechargeable batteries. When we place the vehicle in gear and press on the accelerator, power is converted from DC (stored in the battery) to AC through an inverter for the electric motor. The controller can adjust the vehicle speed by changing the frequency of the AC power. When the brakes are applied or the car is decelerating, the motor becomes a generator and produces power which is sent back to the battery (Regenerative braking).

Now let's take a quick look at the features and components that make the Model S unique.

Induction motor

A powerhouse of EV invented by Nicolas Tesla. It is a three-phase 4-pole AC induction motor that takes a

three-phase AC supply as input and provides rotating mechanical energy. It is capable of producing up to 416HP and 443 lb-ft torque. Its speed depends upon the frequency of the supplied voltage (3-phase AC). This speed can vary from 0 to 18000 rpm and just by varying the frequency of the supplied voltage speed of the motor i.e., the speed of the car can be altered and can be accelerated very fast (particularly it can achieve 100kmph speed from rest in just 2 seconds; fastest accelerating car). That’s why the speed range of EVs is much wider than ICE cars. On the other hand, ICE makes to and fro linear motion which is converted into rotational motion. That’s why the power output of an ICE is always uneven. But in the case of EV inductor motor directly produces rotational motion and uniform power output. That’s why many accessories can be avoided which makes it lighter than ICE (ICE-180kg,140kW; Induction motor- 31.8kg,270kW).

Lithium battery power source

It is a parallel and series combination of commonly used lithium-ion cells. Instead of using a few big cells, Tesla uses many small cells so that glycol coolant can be passed through the gap between lithium cells. The heated glycol is cooled down by passing through a radiator fitted in the front portion of the car. This effective cooling minimizes thermal hotspots and gives better battery pack life. These cells are arranged in detachable modules and 16 modules have around 7000 cells. A low-height battery pack is used which makes the CG of the car lower and provides more stability. Tesla S has a highly efficient battery pack that provides a range of around 402 miles (647 km) on a single recharge. It can also be recharged using various charging methods including a 120-volt outlet, 240-volt outlet, or Tesla`s charging station.

Inverter

DC power is generated from the battery pack, which is converted into AC by this converter. The inverter also controls the frequency of the supply voltage to control the motor speed and controls the amplitude of the supply AC voltage to control the power output of the motor. This inverted is indeed the brain of the car.

Gearbox

Tesla S uses a two-stage reduction gearbox. Power generated by the motor is passed through transmission before reaching the wheels. Transmission controls the speed and torque for different driving conditions. For example, high torque and low speed are required in hill climbing.

Torque * Speed = Power

In the case of EVs single-speed transmission is used as the motor itself is efficient in wide operating conditions. The reverse can also be easily achieved by just reversing the motor rotation direction. After the transmission the reduced speed drive is passed to the differential and rotational motion is provided to the wheel. In the Tesla S, an open differential is used as it can carry more torque.

Regenerative braking

Whenever the accelerator pedal of the Tesla S is released, regenerative braking comes into action. At this time the induction motor works as a generator. The rotor part of it is rotated by the wheels and it generates electricity which is stored in the battery pack. An opposing magnetic field acts Tesla S can also be driven by a single pedal (accelerator pedal) only. For a complete stop, the brake pedal is used. Thus, by converting kinetic energy into electricity range of Tesla S is also increased.

Aerodynamics

The Aerodynamics of a car has a tremendous effect on how the car accelerates, wind noise, and mileage. It is designed in such a way that it can reduce air drag and increase efficiency. Tesla S is one of the most aerodynamic cars having only 0.23 drag coefficient. It has an adjustable air suspension system that can lower the car`s height at a higher speed to reduce air resistance. Its sleek body also helps to reduce resistance. Long sloping roofline and round shape front and rear help to minimize air turbulence. The underside of the car is flat which reduces drag. This design is called a belly pan. The rear spoiler of the car provides downforce and reduces drag which gives the car stability at high speed.

Over-the-air updates

One of the coolest features of Tesla cars is its over-the-air updates. Just like cell phones tesla cars` features are also updated wirelessly. There are two different types of over-the-air updates: software over-the-air (SOTA) and firmware over-the-air (FOTA) updates. SOTA updates have to do with anything software-related that can control the vehicle’s physical controls (like the infotainment and navigation) and electronic processing system. On the other hand, the FOTA updates include updates to the vehicle’s firmware, or the system itself.

Materials used

The incredible raw materials used in the Model S are one of the major secrets of its ultra-high performance and safety. The body and chassis are built from aluminum (190kg) which makes it lighter and helps to maximize the range of the battery and speed of the car. The underbody is built with titanium. The rotor of the induction motor is made of copper whereas the stator is made of copper and steel. The car gains stability from its battery pack. It contains 7104 lithium-ion battery cells that weigh 540 kg (26% of the car's total weight).

Limitations

Though it is highly praised for its extraordinary performance it also has some limitations which are as follows-

Its range is limited.

It can take up to 10 hours to fully charge and a charging point is not available very much.

It has a high price and high maintenance cost.

But as an optimist, we can say with the advancement of time and the popularity of EVs these problems can be removed, and we will put forward to a green society.

Contributors

Satyaky Jana

(B.E. Production Engg. JU 2nd Year)

Meghamita Mukherjee

(B.E. Chemical Engg. JU 2nd Year)