REGENERATIVE BRAKING SYSTEM

Introduction -

      As we all know Brakes are an important part in any kind of automobile. We are growing rapidly and so our automobiles and with this growth rate there is always a necessity to upgrade.

Regenerative Braking systems (RBS) are a type of a kinetic energy recovery system that transfers the kinetic energy of an object in motion into potential or stored energy to slow the vehicle down, and as a result increases fuel efficiency . There are multiple methods of energy conversion in RBSs including spring, flywheel, electromagnetic and hydraulic. More recently, an electromagnetic-flywheel hybrid RBS has emerged as well. Each type of RBS utilizes a different energy conversion or storage method, giving varying efficiency and applications for each type.    

History -

The idea of a brake that could take the kinetic energy it absorbs and turn it into potential energy for later use has been around since the late 1800s. Some of the early attempts of this technology were to install spring type RBS on front wheel drive bicycles or horse-drawn cabs.

The Baku-Tbilisi-Batumi railway started applying RBS in the early 1930s. This is one example of early use of this technology in the railway system.

In the 1950s, Swiss company Oerlikon developed the gyrobus, which utilized flywheel as its energy storage method. The effects of gyroscopic motion on the bus soon resulted in it being discontinued.

In 1967, the American Motor Car Company (AMC) created an electrical energy regeneration brake for their concept electric car, the AMC Amitron. Toyota was the first car manufacturer to commercialize RBS technology in their Prius series hybrid cars.

Since then, RBSs have evolved to be used in almost all electric and hybrid cars, as well as some gas-powered vehicles.

 

Why do we need a Regenerative Braking System?

Whenever we use brakes we lose momentum and cause waste of energy. We are familiar with the start-stop-start-stop motion of an automobile while we are in traffic. It can be a huge waste of time and energy. Getting a car moving needs a big input of power, and every time you hit the brakes all the energy you've built up disappears again, wasted in the brake pads as heat. We are already running out of usable energy so it's our need to store energy as much as possible. 

Graph of heat loss during braking for different automobiles :

What are Regenerative Brakes?

         Electric trains, cars, and other electric vehicles are powered by electric motors  connected to batteries. When you're driving along, energy flows from the batteries to the motors, turning the wheels and providing you with the kinetic energy you need to move. When you stop and hit the brakes, the whole process goes into reverse: electronic circuits cut the power to the motors. Now, your kinetic energy and momentum makes the wheels turn the motors, so the motors work like generators and start producing electricity instead of consuming it. Power flows back from these motor-generators to the batteries, charging them up. So a good proportion of the energy you lose by braking is returned to the batteries and can be reused when you start off again. In practice, regenerative brakes take time to slow things down, so most vehicles that use them also have ordinary (friction) brakes working alongside (that's also a good idea in case the regenerative brakes fail). That's one reason why regenerative brakes don't save 100 percent of your braking energy.

How much energy does it recover?

Unfortunately, the adage “your mileage may vary” applies to regen as well. The amount of energy you can recover depends on how and where you drive. From the powertrain point of view it looks pretty good. The energy conversion efficiencies from chemical to electrical (battery), DC current to AC current (inverter), electrical to mechanical (motor), and torque to force (transmission and wheels) are all quite high and work just as efficiently returning energy into the battery. The bigger problem is aerodynamic losses and higher speeds and rolling friction of the tires. These both act to slow the car, but the energy dissipated cannot be recovered. We must also remember that, even though the battery-to-wheel conversion efficiency is pretty good (up to 80% or so), the energy makes a full circle back into the battery and it gets converted twice for a net efficiency of at most 80% * 80% = 64%.

When does it work?

There are a number of goals and restrictions when using regenerative braking. Tesla Motors is still putting the final touches on the regen torque profile to achieve the goals within the constraints.

            1) Safety :

            Negative torque applied to the rear wheels can cause a car to become unstable. Since regen braking is a source of negative torque, the Tesla Roadster uses the traction control system to limit regen if the rear wheels start to slip.

             

            2) Performance :

            Regenerative braking can enhance the driving experience in ways not available with a traditional internal combustion engine (ICE). Driving with regen is fun! Having that instant positive and negative torque command right at your toes really makes you feel in control.

             

            3) Limitations :

            Regenerative braking is necessarily limited when the batteries are fully charged. Because the additional charge from regenerative braking would cause the voltage of a full battery to rise above a safe level, our motor controller will limit regen torque in this case.

Working of  Regenerative braking :-

Applications :

1) Hybrid and Electric Cars -

Modern hybrid and electric cars both utilize an electric engine to power the car which makes applying regenerative braking very simple and efficient. In the vast majority of these cars, the transmission of the car is set up such that when the driver applies the brakes, the electric motor reverses itself and applies a resistance to the wheels rather than power. The resistance applied to the wheels is then put through the electric motor where it is used to recharge the batteries.

          In high performance electric cars, improving the feel of the car is very important to car manufacturers. Many customers support electric supercars but are against purchasing them because of the lack of high performance feel. One important aspect of this feel is engine braking. In a standard internal combustion engine, once power is not being applied to the engine, the natural friction inside the engine works to slow the vehicle down. In electric cars, this friction force does not apply; however, car companies such as Mercedes and Porsche have begun to use regenerative braking systems to give the driver the same feel of a gas-powered car while recovering energy for the batteries.

2) Auto Racing -

In 2009, Formula 1 (a common type of race car) introduced a regenerative braking system called the Kinetic Energy Recovery System (KERS). The uptake of the system was slow at first and had no teams using it in the 2010 season; however, improvements to the system in the 2011 season made it extremely beneficial to cars and almost all teams adopted some form of the system. Formula one cars use either a four flywheel or electric generator system to store energy under braking. This stored energy can then be utilized by the driver by pushing a button on their steering wheel. The FIA restricts the use to 6.67 seconds per lap during which the system gives the car an extra 81 hp.

 

The future for regenerative braking : 

There are a number of subjective decisions we have to make concerning the regen profile. Some people like regen to work all the way to 0 mph, bringing the car to a complete stop. Others like to coast that last 2 to 3 mph. Almost everyone likes the car to regen when you take your foot off of the throttle pedal, but there are some who would prefer the car to coast when you do this. They would prefer the regen to be tied to the application of the brake pedal. Almost everyone likes the more aggressive regen available to the driver, but a few people are more comfortable with a traditional ICE-like compression braking and coast-down profile. Ultimately, the Tesla Roadster is a sports car and the regen profile will be fine tuned for sports car driving.

One day everyone will drive electric cars and regen will be a big part of what will make them fun to drive, efficient, and safe. The recent research and development to integrate the powertrain and brake systems to provide better traction and stability control can only be made easier by the use of electric drive systems. One thing I learned from the traction control work I did on the frozen lake is that traction control is a much simpler problem to solve when you have precise and instant control of torque through the AC induction motor controller. Further integration of antilock braking systems with the motor controller would allow the motor to take over more of the vehicle braking. It’s very exciting to be working at the forefront of these possibilities.

By -

1) AAYUSH SURAWAR.

2) SAMARTH TAKBHATE.

3) GOPAL TAPADIYA.

4) SHIVAM TAPRE.

5) UMESH WANARE.